aboutsummaryrefslogtreecommitdiffstats
path: root/guides/source/getting_started.md
blob: 0cc3f9b276ec95a4e70c1fe3154faf16759f05a6 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON http://guides.rubyonrails.org.**

Getting Started with Rails
==========================

This guide covers getting up and running with Ruby on Rails.

After reading this guide, you will know:

* How to install Rails, create a new Rails application, and connect your
  application to a database.
* The general layout of a Rails application.
* The basic principles of MVC (Model, View, Controller) and RESTful design.
* How to quickly generate the starting pieces of a Rails application.

--------------------------------------------------------------------------------

Guide Assumptions
-----------------

This guide is designed for beginners who want to get started with a Rails
application from scratch. It does not assume that you have any prior experience
with Rails.

Rails is a web application framework running on the Ruby programming language.
If you have no prior experience with Ruby, you will find a very steep learning
curve diving straight into Rails. There are several curated lists of online resources
for learning Ruby:

* [Official Ruby Programming Language website](https://www.ruby-lang.org/en/documentation/)
* [List of Free Programming Books](https://github.com/vhf/free-programming-books/blob/master/free-programming-books.md#ruby)

Be aware that some resources, while still excellent, cover versions of Ruby as old as
1.6, and commonly 1.8, and will not include some syntax that you will see in day-to-day
development with Rails.

What is Rails?
--------------

Rails is a web application development framework written in the Ruby programming language.
It is designed to make programming web applications easier by making assumptions
about what every developer needs to get started. It allows you to write less
code while accomplishing more than many other languages and frameworks.
Experienced Rails developers also report that it makes web application
development more fun.

Rails is opinionated software. It makes the assumption that there is a "best"
way to do things, and it's designed to encourage that way - and in some cases to
discourage alternatives. If you learn "The Rails Way" you'll probably discover a
tremendous increase in productivity. If you persist in bringing old habits from
other languages to your Rails development, and trying to use patterns you
learned elsewhere, you may have a less happy experience.

The Rails philosophy includes two major guiding principles:

* **Don't Repeat Yourself:** DRY is a principle of software development which
  states that "Every piece of knowledge must have a single, unambiguous, authoritative
  representation within a system." By not writing the same information over and over
  again, our code is more maintainable, more extensible, and less buggy.
* **Convention Over Configuration:** Rails has opinions about the best way to do many
  things in a web application, and defaults to this set of conventions, rather than
  require that you specify minutiae through endless configuration files.

Creating a New Rails Project
----------------------------
The best way to read this guide is to follow it step by step. All steps are
essential to run this example application and no additional code or steps are
needed.

By following along with this guide, you'll create a Rails project called
`blog`, a (very) simple weblog. Before you can start building the application,
you need to make sure that you have Rails itself installed.

TIP: The examples below use `$` to represent your terminal prompt in a UNIX-like OS,
though it may have been customized to appear differently. If you are using Windows,
your prompt will look something like `c:\source_code>`

### Installing Rails

Before you install Rails, you should check to make sure that your system has the
proper prerequisites installed. These include Ruby and SQLite3.

Open up a command line prompt. On macOS open Terminal.app, on Windows choose
"Run" from your Start menu and type 'cmd.exe'. Any commands prefaced with a
dollar sign `$` should be run in the command line. Verify that you have a
current version of Ruby installed:

```bash
$ ruby -v
ruby 2.5.0
```

Rails requires Ruby version 2.4.1 or later. If the version number returned is
less than that number, you'll need to install a fresh copy of Ruby.

TIP: To quickly install Ruby and Ruby on Rails on your system in Windows, you can use
[Rails Installer](http://railsinstaller.org). For more installation methods for most
Operating Systems take a look at [ruby-lang.org](https://www.ruby-lang.org/en/documentation/installation/).

If you are working on Windows, you should also install the
[Ruby Installer Development Kit](https://rubyinstaller.org/downloads/).

You will also need an installation of the SQLite3 database.
Many popular UNIX-like OSes ship with an acceptable version of SQLite3.
On Windows, if you installed Rails through Rails Installer, you
already have SQLite installed. Others can find installation instructions
at the [SQLite3 website](https://www.sqlite.org).
Verify that it is correctly installed and in your PATH:

```bash
$ sqlite3 --version
```

The program should report its version.

To install Rails, use the `gem install` command provided by RubyGems:

```bash
$ gem install rails
```

To verify that you have everything installed correctly, you should be able to
run the following:

```bash
$ rails --version
```

If it says something like "Rails 5.1.1", you are ready to continue.

### Creating the Blog Application

Rails comes with a number of scripts called generators that are designed to make
your development life easier by creating everything that's necessary to start
working on a particular task. One of these is the new application generator,
which will provide you with the foundation of a fresh Rails application so that
you don't have to write it yourself.

To use this generator, open a terminal, navigate to a directory where you have
rights to create files, and type:

```bash
$ rails new blog
```

This will create a Rails application called Blog in a `blog` directory and
install the gem dependencies that are already mentioned in `Gemfile` using
`bundle install`.

NOTE: If you're using Windows Subsystem for Linux then there are currently some
limitations on file system notifications that mean you should disable the `spring`
and `listen` gems which you can do by running `rails new blog --skip-spring --skip-listen`.

TIP: You can see all of the command line options that the Rails application
builder accepts by running `rails new -h`.

After you create the blog application, switch to its folder:

```bash
$ cd blog
```

The `blog` directory has a number of auto-generated files and folders that make
up the structure of a Rails application. Most of the work in this tutorial will
happen in the `app` folder, but here's a basic rundown on the function of each
of the files and folders that Rails created by default:

| File/Folder | Purpose |
| ----------- | ------- |
|app/|Contains the controllers, models, views, helpers, mailers, channels, jobs, and assets for your application. You'll focus on this folder for the remainder of this guide.|
|bin/|Contains the rails script that starts your app and can contain other scripts you use to setup, update, deploy, or run your application.|
|config/|Configure your application's routes, database, and more. This is covered in more detail in [Configuring Rails Applications](configuring.html).|
|config.ru|Rack configuration for Rack based servers used to start the application. For more information about Rack, see the [Rack website](https://rack.github.io/).|
|db/|Contains your current database schema, as well as the database migrations.|
|Gemfile<br>Gemfile.lock|These files allow you to specify what gem dependencies are needed for your Rails application. These files are used by the Bundler gem. For more information about Bundler, see the [Bundler website](https://bundler.io).|
|lib/|Extended modules for your application.|
|log/|Application log files.|
|package.json|This file allows you to specify what npm dependencies are needed for your Rails application. This file is used by Yarn. For more information about Yarn, see the [Yarn website](https://yarnpkg.com/lang/en/).|
|public/|The only folder seen by the world as-is. Contains static files and compiled assets.|
|Rakefile|This file locates and loads tasks that can be run from the command line. The task definitions are defined throughout the components of Rails. Rather than changing `Rakefile`, you should add your own tasks by adding files to the `lib/tasks` directory of your application.|
|README.md|This is a brief instruction manual for your application. You should edit this file to tell others what your application does, how to set it up, and so on.|
|storage/|Active Storage files for Disk Service. This is covered in [Active Storage Overview](active_storage_overview.html).|
|test/|Unit tests, fixtures, and other test apparatus. These are covered in [Testing Rails Applications](testing.html).|
|tmp/|Temporary files (like cache and pid files).|
|vendor/|A place for all third-party code. In a typical Rails application this includes vendored gems.|
|.gitignore|This file tells git which files (or patterns) it should ignore. See [GitHub - Ignoring files](https://help.github.com/articles/ignoring-files) for more info about ignoring files.
|.ruby-version|This file contains the default Ruby version.|

Hello, Rails!
-------------

To begin with, let's get some text up on screen quickly. To do this, you need to
get your Rails application server running.

### Starting up the Web Server

You actually have a functional Rails application already. To see it, you need to
start a web server on your development machine. You can do this by running the
following in the `blog` directory:

```bash
$ rails server
```

TIP: If you are using Windows, you have to pass the scripts under the `bin`
folder directly to the Ruby interpreter e.g. `ruby bin\rails server`.

TIP: Compiling CoffeeScript and JavaScript asset compression requires you
have a JavaScript runtime available on your system, in the absence
of a runtime you will see an `execjs` error during asset compilation.
Usually macOS and Windows come with a JavaScript runtime installed.
Rails adds the `mini_racer` gem to the generated `Gemfile` in a
commented line for new apps and you can uncomment if you need it.
`therubyrhino` is the recommended runtime for JRuby users and is added by
default to the `Gemfile` in apps generated under JRuby. You can investigate
all the supported runtimes at [ExecJS](https://github.com/rails/execjs#readme).

This will fire up Puma, a web server distributed with Rails by default. To see
your application in action, open a browser window and navigate to
<http://localhost:3000>. You should see the Rails default information page:

![Welcome aboard screenshot](images/getting_started/rails_welcome.png)

TIP: To stop the web server, hit Ctrl+C in the terminal window where it's
running. To verify the server has stopped you should see your command prompt
cursor again. For most UNIX-like systems including macOS this will be a
dollar sign `$`. In development mode, Rails does not generally require you to
restart the server; changes you make in files will be automatically picked up by
the server.

The "Welcome aboard" page is the _smoke test_ for a new Rails application: it
makes sure that you have your software configured correctly enough to serve a
page.

### Say "Hello", Rails

To get Rails saying "Hello", you need to create at minimum a _controller_ and a
_view_.

A controller's purpose is to receive specific requests for the application.
_Routing_ decides which controller receives which requests. Often, there is more
than one route to each controller, and different routes can be served by
different _actions_. Each action's purpose is to collect information to provide
it to a view.

A view's purpose is to display this information in a human readable format. An
important distinction to make is that it is the _controller_, not the view,
where information is collected. The view should just display that information.
By default, view templates are written in a language called eRuby (Embedded
Ruby) which is processed by the request cycle in Rails before being sent to the
user.

To create a new controller, you will need to run the "controller" generator and
tell it you want a controller called "Welcome" with an action called "index",
just like this:

```bash
$ rails generate controller Welcome index
```

Rails will create several files and a route for you.

```bash
create  app/controllers/welcome_controller.rb
 route  get 'welcome/index'
invoke  erb
create    app/views/welcome
create    app/views/welcome/index.html.erb
invoke  test_unit
create    test/controllers/welcome_controller_test.rb
invoke  helper
create    app/helpers/welcome_helper.rb
invoke    test_unit
invoke  assets
invoke    coffee
create      app/assets/javascripts/welcome.coffee
invoke    scss
create      app/assets/stylesheets/welcome.scss
```

Most important of these are of course the controller, located at
`app/controllers/welcome_controller.rb` and the view, located at
`app/views/welcome/index.html.erb`.

Open the `app/views/welcome/index.html.erb` file in your text editor. Delete all
of the existing code in the file, and replace it with the following single line
of code:

```html
<h1>Hello, Rails!</h1>
```

### Setting the Application Home Page

Now that we have made the controller and view, we need to tell Rails when we
want "Hello, Rails!" to show up. In our case, we want it to show up when we
navigate to the root URL of our site, <http://localhost:3000>. At the moment,
"Welcome aboard" is occupying that spot.

Next, you have to tell Rails where your actual home page is located.

Open the file `config/routes.rb` in your editor.

```ruby
Rails.application.routes.draw do
  get 'welcome/index'

  # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html
end
```

This is your application's _routing file_ which holds entries in a special
[DSL (domain-specific language)](https://en.wikipedia.org/wiki/Domain-specific_language)
that tells Rails how to connect incoming requests to
controllers and actions.
Edit this file by adding the line of code `root 'welcome#index'`.
It should look something like the following:

```ruby
Rails.application.routes.draw do
  get 'welcome/index'

  root 'welcome#index'
end
```

`root 'welcome#index'` tells Rails to map requests to the root of the
application to the welcome controller's index action and `get 'welcome/index'`
tells Rails to map requests to <http://localhost:3000/welcome/index> to the
welcome controller's index action. This was created earlier when you ran the
controller generator (`rails generate controller Welcome index`).

Launch the web server again if you stopped it to generate the controller (`rails
server`) and navigate to <http://localhost:3000> in your browser. You'll see the
"Hello, Rails!" message you put into `app/views/welcome/index.html.erb`,
indicating that this new route is indeed going to `WelcomeController`'s `index`
action and is rendering the view correctly.

TIP: For more information about routing, refer to [Rails Routing from the Outside In](routing.html).

Getting Up and Running
----------------------

Now that you've seen how to create a controller, an action, and a view, let's
create something with a bit more substance.

In the Blog application, you will now create a new _resource_. A resource is the
term used for a collection of similar objects, such as articles, people, or
animals.
You can create, read, update, and destroy items for a resource and these
operations are referred to as _CRUD_ operations.

Rails provides a `resources` method which can be used to declare a standard REST
resource. You need to add the _article resource_ to the
`config/routes.rb` so the file will look as follows:

```ruby
Rails.application.routes.draw do
  get 'welcome/index'

  resources :articles

  root 'welcome#index'
end
```

If you run `rails routes`, you'll see that it has defined routes for all the
standard RESTful actions.  The meaning of the prefix column (and other columns)
will be seen later, but for now notice that Rails has inferred the
singular form `article` and makes meaningful use of the distinction.

```bash
$ rails routes
       Prefix Verb   URI Pattern                  Controller#Action
welcome_index GET    /welcome/index(.:format)     welcome#index
     articles GET    /articles(.:format)          articles#index
              POST   /articles(.:format)          articles#create
  new_article GET    /articles/new(.:format)      articles#new
 edit_article GET    /articles/:id/edit(.:format) articles#edit
      article GET    /articles/:id(.:format)      articles#show
              PATCH  /articles/:id(.:format)      articles#update
              PUT    /articles/:id(.:format)      articles#update
              DELETE /articles/:id(.:format)      articles#destroy
         root GET    /                            welcome#index
```

In the next section, you will add the ability to create new articles in your
application and be able to view them. This is the "C" and the "R" from CRUD:
create and read. The form for doing this will look like this:

![The new article form](images/getting_started/new_article.png)

It will look a little basic for now, but that's ok. We'll look at improving the
styling for it afterwards.

### Laying down the groundwork

Firstly, you need a place within the application to create a new article. A
great place for that would be at `/articles/new`. With the route already
defined, requests can now be made to `/articles/new` in the application.
Navigate to <http://localhost:3000/articles/new> and you'll see a routing
error:

![Another routing error, uninitialized constant ArticlesController](images/getting_started/routing_error_no_controller.png)

This error occurs because the route needs to have a controller defined in order
to serve the request. The solution to this particular problem is simple: create
a controller called `ArticlesController`. You can do this by running this
command:

```bash
$ rails generate controller Articles
```

If you open up the newly generated `app/controllers/articles_controller.rb`
you'll see a fairly empty controller:

```ruby
class ArticlesController < ApplicationController
end
```

A controller is simply a class that is defined to inherit from
`ApplicationController`.
It's inside this class that you'll define methods that will become the actions
for this controller. These actions will perform CRUD operations on the articles
within our system.

NOTE: There are `public`, `private` and `protected` methods in Ruby,
but only `public` methods can be actions for controllers.
For more details check out [Programming Ruby](http://www.ruby-doc.org/docs/ProgrammingRuby/).

If you refresh <http://localhost:3000/articles/new> now, you'll get a new error:

![Unknown action new for ArticlesController!](images/getting_started/unknown_action_new_for_articles.png)

This error indicates that Rails cannot find the `new` action inside the
`ArticlesController` that you just generated. This is because when controllers
are generated in Rails they are empty by default, unless you tell it
your desired actions during the generation process.

To manually define an action inside a controller, all you need to do is to
define a new method inside the controller. Open
`app/controllers/articles_controller.rb` and inside the `ArticlesController`
class, define the `new` method so that your controller now looks like this:

```ruby
class ArticlesController < ApplicationController
  def new
  end
end
```

With the `new` method defined in `ArticlesController`, if you refresh
<http://localhost:3000/articles/new> you'll see another error:

![Template is missing for articles/new]
(images/getting_started/template_is_missing_articles_new.png)

You're getting this error now because Rails expects plain actions like this one
to have views associated with them to display their information. With no view
available, Rails will raise an exception.

Let's look at the full error message again:

>ArticlesController#new is missing a template for this request format and variant. request.formats: ["text/html"] request.variant: [] NOTE! For XHR/Ajax or API requests, this action would normally respond with 204 No Content: an empty white screen. Since you're loading it in a web browser, we assume that you expected to actually render a template, not… nothing, so we're showing an error to be extra-clear. If you expect 204 No Content, carry on. That's what you'll get from an XHR or API request. Give it a shot.

That's quite a lot of text! Let's quickly go through and understand what each
part of it means.

The first part identifies which template is missing. In this case, it's the
`articles/new` template. Rails will first look for this template. If not found,
then it will attempt to load a template called `application/new`. It looks for
one here because the `ArticlesController` inherits from `ApplicationController`.

The next part of the message contains `request.formats` which specifies
the format of template to be served in response. It is set to `text/html` as we
requested this page via browser, so Rails is looking for an HTML template.
`request.variant` specifies what kind of physical devices would be served by
the response and helps Rails determine which template to use in the response.
It is empty because no information has been provided.

The simplest template that would work in this case would be one located at
`app/views/articles/new.html.erb`. The extension of this file name is important:
the first extension is the _format_ of the template, and the second extension
is the _handler_ that will be used to render the template. Rails is attempting
to find a template called `articles/new` within `app/views` for the
application. The format for this template can only be `html` and the default
handler for HTML is `erb`. Rails uses other handlers for other formats.
`builder` handler is used to build XML templates and `coffee` handler uses
CoffeeScript to build JavaScript templates. Since you want to create a new
HTML form, you will be using the `ERB` language which is designed to embed Ruby
in HTML.

Therefore the file should be called `articles/new.html.erb` and needs to be
located inside the `app/views` directory of the application.

Go ahead now and create a new file at `app/views/articles/new.html.erb` and
write this content in it:

```html
<h1>New Article</h1>
```

When you refresh <http://localhost:3000/articles/new> you'll now see that the
page has a title. The route, controller, action, and view are now working
harmoniously! It's time to create the form for a new article.

### The first form

To create a form within this template, you will use a *form
builder*. The primary form builder for Rails is provided by a helper
method called `form_with`. To use this method, add this code into
`app/views/articles/new.html.erb`:

```html+erb
<%= form_with scope: :article, local: true do |form| %>
  <p>
    <%= form.label :title %><br>
    <%= form.text_field :title %>
  </p>

  <p>
    <%= form.label :text %><br>
    <%= form.text_area :text %>
  </p>

  <p>
    <%= form.submit %>
  </p>
<% end %>
```

If you refresh the page now, you'll see the exact same form from our example above.
Building forms in Rails is really just that easy!

When you call `form_with`, you pass it an identifying scope for this
form. In this case, it's the symbol `:article`. This tells the `form_with`
helper what this form is for. Inside the block for this method, the
`FormBuilder` object - represented by `form` - is used to build two labels and two
text fields, one each for the title and text of an article. Finally, a call to
`submit` on the `form` object will create a submit button for the form.

There's one problem with this form though. If you inspect the HTML that is
generated, by viewing the source of the page, you will see that the `action`
attribute for the form is pointing at `/articles/new`. This is a problem because
this route goes to the very page that you're on right at the moment, and that
route should only be used to display the form for a new article.

The form needs to use a different URL in order to go somewhere else.
This can be done quite simply with the `:url` option of `form_with`.
Typically in Rails, the action that is used for new form submissions
like this is called "create", and so the form should be pointed to that action.

Edit the `form_with` line inside `app/views/articles/new.html.erb` to look like
this:

```html+erb
<%= form_with scope: :article, url: articles_path, local: true do |form| %>
```

In this example, the `articles_path` helper is passed to the `:url` option.
To see what Rails will do with this, we look back at the output of
`rails routes`:

```bash
$ rails routes
      Prefix Verb   URI Pattern                  Controller#Action
welcome_index GET    /welcome/index(.:format)     welcome#index
     articles GET    /articles(.:format)          articles#index
              POST   /articles(.:format)          articles#create
  new_article GET    /articles/new(.:format)      articles#new
 edit_article GET    /articles/:id/edit(.:format) articles#edit
      article GET    /articles/:id(.:format)      articles#show
              PATCH  /articles/:id(.:format)      articles#update
              PUT    /articles/:id(.:format)      articles#update
              DELETE /articles/:id(.:format)      articles#destroy
         root GET    /                            welcome#index
```

The `articles_path` helper tells Rails to point the form to the URI Pattern
associated with the `articles` prefix; and the form will (by default) send a
`POST` request to that route. This is associated with the `create` action of
the current controller, the `ArticlesController`.

With the form and its associated route defined, you will be able to fill in the
form and then click the submit button to begin the process of creating a new
article, so go ahead and do that. When you submit the form, you should see a
familiar error:

![Unknown action create for ArticlesController]
(images/getting_started/unknown_action_create_for_articles.png)

You now need to create the `create` action within the `ArticlesController` for
this to work.

NOTE: By default `form_with` submits forms using Ajax thereby skipping full page
redirects. To make this guide easier to get into we've disabled that with
`local: true` for now.

### Creating articles

To make the "Unknown action" go away, you can define a `create` action within
the `ArticlesController` class in `app/controllers/articles_controller.rb`,
underneath the `new` action, as shown:

```ruby
class ArticlesController < ApplicationController
  def new
  end

  def create
  end
end
```

If you re-submit the form now, you may not see any change on the page. Don't worry!
This is because Rails by default returns `204 No Content` response for an action if
we don't specify what the response should be. We just added the `create` action
but didn't specify anything about how the response should be. In this case, the
`create` action should save our new article to the database.

When a form is submitted, the fields of the form are sent to Rails as
_parameters_. These parameters can then be referenced inside the controller
actions, typically to perform a particular task. To see what these parameters
look like, change the `create` action to this:

```ruby
def create
  render plain: params[:article].inspect
end
```

The `render` method here is taking a very simple hash with a key of `:plain` and
value of `params[:article].inspect`. The `params` method is the object which
represents the parameters (or fields) coming in from the form. The `params`
method returns an `ActionController::Parameters` object, which
allows you to access the keys of the hash using either strings or symbols. In
this situation, the only parameters that matter are the ones from the form.

TIP: Ensure you have a firm grasp of the `params` method, as you'll use it fairly regularly. Let's consider an example URL: **http://www.example.com/?username=dhh&email=dhh@email.com**. In this URL, `params[:username]` would equal "dhh" and `params[:email]` would equal "dhh@email.com".

If you re-submit the form one more time, you'll see something that looks like the following:

```ruby
<ActionController::Parameters {"title"=>"First Article!", "text"=>"This is my first article."} permitted: false>
```

This action is now displaying the parameters for the article that are coming in
from the form. However, this isn't really all that helpful. Yes, you can see the
parameters but nothing in particular is being done with them.

### Creating the Article model

Models in Rails use a singular name, and their corresponding database tables
use a plural name. Rails provides a generator for creating models, which most
Rails developers tend to use when creating new models. To create the new model,
run this command in your terminal:

```bash
$ rails generate model Article title:string text:text
```

With that command we told Rails that we want an `Article` model, together
with a _title_ attribute of type string, and a _text_ attribute
of type text. Those attributes are automatically added to the `articles`
table in the database and mapped to the `Article` model.

Rails responded by creating a bunch of files. For now, we're only interested
in `app/models/article.rb` and `db/migrate/20140120191729_create_articles.rb`
(your name could be a bit different). The latter is responsible for creating
the database structure, which is what we'll look at next.

TIP: Active Record is smart enough to automatically map column names to model
attributes, which means you don't have to declare attributes inside Rails
models, as that will be done automatically by Active Record.

### Running a Migration

As we've just seen, `rails generate model` created a _database migration_ file
inside the `db/migrate` directory. Migrations are Ruby classes that are
designed to make it simple to create and modify database tables. Rails uses
rake commands to run migrations, and it's possible to undo a migration after
it's been applied to your database. Migration filenames include a timestamp to
ensure that they're processed in the order that they were created.

If you look in the `db/migrate/YYYYMMDDHHMMSS_create_articles.rb` file
(remember, yours will have a slightly different name), here's what you'll find:

```ruby
class CreateArticles < ActiveRecord::Migration[5.0]
  def change
    create_table :articles do |t|
      t.string :title
      t.text :text

      t.timestamps
    end
  end
end
```

The above migration creates a method named `change` which will be called when
you run this migration. The action defined in this method is also reversible,
which means Rails knows how to reverse the change made by this migration,
in case you want to reverse it later. When you run this migration it will create
an `articles` table with one string column and a text column. It also creates
two timestamp fields to allow Rails to track article creation and update times.

TIP: For more information about migrations, refer to [Active Record Migrations]
(active_record_migrations.html).

At this point, you can use a rails command to run the migration:

```bash
$ rails db:migrate
```

Rails will execute this migration command and tell you it created the Articles
table.

```bash
==  CreateArticles: migrating ==================================================
-- create_table(:articles)
   -> 0.0019s
==  CreateArticles: migrated (0.0020s) =========================================
```

NOTE. Because you're working in the development environment by default, this
command will apply to the database defined in the `development` section of your
`config/database.yml` file. If you would like to execute migrations in another
environment, for instance in production, you must explicitly pass it when
invoking the command: `rails db:migrate RAILS_ENV=production`.

### Saving data in the controller

Back in `ArticlesController`, we need to change the `create` action
to use the new `Article` model to save the data in the database.
Open `app/controllers/articles_controller.rb` and change the `create` action to
look like this:

```ruby
def create
  @article = Article.new(params[:article])

  @article.save
  redirect_to @article
end
```

Here's what's going on: every Rails model can be initialized with its
respective attributes, which are automatically mapped to the respective
database columns. In the first line we do just that (remember that
`params[:article]` contains the attributes we're interested in). Then,
`@article.save` is responsible for saving the model in the database. Finally,
we redirect the user to the `show` action, which we'll define later.

TIP: You might be wondering why the `A` in `Article.new` is capitalized above, whereas most other references to articles in this guide have used lowercase. In this context, we are referring to the class named `Article` that is defined in `app/models/article.rb`. Class names in Ruby must begin with a capital letter.

TIP: As we'll see later, `@article.save` returns a boolean indicating whether
the article was saved or not.

If you now go to <http://localhost:3000/articles/new> you'll *almost* be able
to create an article. Try it! You should get an error that looks like this:

![Forbidden attributes for new article]
(images/getting_started/forbidden_attributes_for_new_article.png)

Rails has several security features that help you write secure applications,
and you're running into one of them now. This one is called [strong parameters](action_controller_overview.html#strong-parameters),
which requires us to tell Rails exactly which parameters are allowed into our
controller actions.

Why do you have to bother? The ability to grab and automatically assign all
controller parameters to your model in one shot makes the programmer's job
easier, but this convenience also allows malicious use. What if a request to
the server was crafted to look like a new article form submit but also included
extra fields with values that violated your application's integrity? They would
be 'mass assigned' into your model and then into the database along with the
good stuff - potentially breaking your application or worse.

We have to whitelist our controller parameters to prevent wrongful mass
assignment. In this case, we want to both allow and require the `title` and
`text` parameters for valid use of `create`. The syntax for this introduces
`require` and `permit`. The change will involve one line in the `create` action:

```ruby
  @article = Article.new(params.require(:article).permit(:title, :text))
```

This is often factored out into its own method so it can be reused by multiple
actions in the same controller, for example `create` and `update`. Above and
beyond mass assignment issues, the method is often made `private` to make sure
it can't be called outside its intended context. Here is the result:

```ruby
def create
  @article = Article.new(article_params)

  @article.save
  redirect_to @article
end

private
  def article_params
    params.require(:article).permit(:title, :text)
  end
```

TIP: For more information, refer to the reference above and
[this blog article about Strong Parameters]
(https://weblog.rubyonrails.org/2012/3/21/strong-parameters/).

### Showing Articles

If you submit the form again now, Rails will complain about not finding the
`show` action. That's not very useful though, so let's add the `show` action
before proceeding.

As we have seen in the output of `rails routes`, the route for `show` action is
as follows:

```
article GET    /articles/:id(.:format)      articles#show
```

The special syntax `:id` tells rails that this route expects an `:id`
parameter, which in our case will be the id of the article.

As we did before, we need to add the `show` action in
`app/controllers/articles_controller.rb` and its respective view.

NOTE: A frequent practice is to place the standard CRUD actions in each
controller in the following order: `index`, `show`, `new`, `edit`, `create`, `update`
and `destroy`. You may use any order you choose, but keep in mind that these
are public methods; as mentioned earlier in this guide, they must be placed
before declaring `private` visibility in the controller.

Given that, let's add the `show` action, as follows:

```ruby
class ArticlesController < ApplicationController
  def show
    @article = Article.find(params[:id])
  end

  def new
  end

  # snippet for brevity
```

A couple of things to note. We use `Article.find` to find the article we're
interested in, passing in `params[:id]` to get the `:id` parameter from the
request. We also use an instance variable (prefixed with `@`) to hold a
reference to the article object. We do this because Rails will pass all instance
variables to the view.

Now, create a new file `app/views/articles/show.html.erb` with the following
content:

```html+erb
<p>
  <strong>Title:</strong>
  <%= @article.title %>
</p>

<p>
  <strong>Text:</strong>
  <%= @article.text %>
</p>
```

With this change, you should finally be able to create new articles.
Visit <http://localhost:3000/articles/new> and give it a try!

![Show action for articles](images/getting_started/show_action_for_articles.png)

### Listing all articles

We still need a way to list all our articles, so let's do that.
The route for this as per output of `rails routes` is:

```
articles GET    /articles(.:format)          articles#index
```

Add the corresponding `index` action for that route inside the
`ArticlesController` in the `app/controllers/articles_controller.rb` file.
When we write an `index` action, the usual practice is to place it as the
first method in the controller. Let's do it:

```ruby
class ArticlesController < ApplicationController
  def index
    @articles = Article.all
  end

  def show
    @article = Article.find(params[:id])
  end

  def new
  end

  # snippet for brevity
```

And then finally, add the view for this action, located at
`app/views/articles/index.html.erb`:

```html+erb
<h1>Listing articles</h1>

<table>
  <tr>
    <th>Title</th>
    <th>Text</th>
    <th></th>
  </tr>

  <% @articles.each do |article| %>
    <tr>
      <td><%= article.title %></td>
      <td><%= article.text %></td>
      <td><%= link_to 'Show', article_path(article) %></td>
    </tr>
  <% end %>
</table>
```

Now if you go to <http://localhost:3000/articles> you will see a list of all the
articles that you have created.

### Adding links

You can now create, show, and list articles. Now let's add some links to
navigate through pages.

Open `app/views/welcome/index.html.erb` and modify it as follows:

```html+erb
<h1>Hello, Rails!</h1>
<%= link_to 'My Blog', controller: 'articles' %>
```

The `link_to` method is one of Rails' built-in view helpers. It creates a
hyperlink based on text to display and where to go - in this case, to the path
for articles.

Let's add links to the other views as well, starting with adding this
"New Article" link to `app/views/articles/index.html.erb`, placing it above the
`<table>` tag:

```erb
<%= link_to 'New article', new_article_path %>
```

This link will allow you to bring up the form that lets you create a new article.

Now, add another link in `app/views/articles/new.html.erb`, underneath the
form, to go back to the `index` action:

```erb
<%= form_with scope: :article, url: articles_path, local: true do |form| %>
  ...
<% end %>

<%= link_to 'Back', articles_path %>
```

Finally, add a link to the `app/views/articles/show.html.erb` template to
go back to the `index` action as well, so that people who are viewing a single
article can go back and view the whole list again:

```html+erb
<p>
  <strong>Title:</strong>
  <%= @article.title %>
</p>

<p>
  <strong>Text:</strong>
  <%= @article.text %>
</p>

<%= link_to 'Back', articles_path %>
```

TIP: If you want to link to an action in the same controller, you don't need to
specify the `:controller` option, as Rails will use the current controller by
default.

TIP: In development mode (which is what you're working in by default), Rails
reloads your application with every browser request, so there's no need to stop
and restart the web server when a change is made.

### Adding Some Validation

The model file, `app/models/article.rb` is about as simple as it can get:

```ruby
class Article < ApplicationRecord
end
```

There isn't much to this file - but note that the `Article` class inherits from
`ApplicationRecord`. `ApplicationRecord` inherits from `ActiveRecord::Base`
which supplies a great deal of functionality to your Rails models for free,
including basic database CRUD (Create, Read, Update, Destroy) operations, data
validation, as well as sophisticated search support and the ability to relate
multiple models to one another.

Rails includes methods to help you validate the data that you send to models.
Open the `app/models/article.rb` file and edit it:

```ruby
class Article < ApplicationRecord
  validates :title, presence: true,
                    length: { minimum: 5 }
end
```

These changes will ensure that all articles have a title that is at least five
characters long. Rails can validate a variety of conditions in a model,
including the presence or uniqueness of columns, their format, and the
existence of associated objects. Validations are covered in detail in [Active
Record Validations](active_record_validations.html).

With the validation now in place, when you call `@article.save` on an invalid
article, it will return `false`. If you open
`app/controllers/articles_controller.rb` again, you'll notice that we don't
check the result of calling `@article.save` inside the `create` action.
If `@article.save` fails in this situation, we need to show the form back to the
user. To do this, change the `new` and `create` actions inside
`app/controllers/articles_controller.rb` to these:

```ruby
def new
  @article = Article.new
end

def create
  @article = Article.new(article_params)

  if @article.save
    redirect_to @article
  else
    render 'new'
  end
end

private
  def article_params
    params.require(:article).permit(:title, :text)
  end
```

The `new` action is now creating a new instance variable called `@article`, and
you'll see why that is in just a few moments.

Notice that inside the `create` action we use `render` instead of `redirect_to`
when `save` returns `false`. The `render` method is used so that the `@article`
object is passed back to the `new` template when it is rendered. This rendering
is done within the same request as the form submission, whereas the
`redirect_to` will tell the browser to issue another request.

If you reload
<http://localhost:3000/articles/new> and
try to save an article without a title, Rails will send you back to the
form, but that's not very useful. You need to tell the user that
something went wrong. To do that, you'll modify
`app/views/articles/new.html.erb` to check for error messages:

```html+erb
<%= form_with scope: :article, url: articles_path, local: true do |form| %>

  <% if @article.errors.any? %>
    <div id="error_explanation">
      <h2>
        <%= pluralize(@article.errors.count, "error") %> prohibited
        this article from being saved:
      </h2>
      <ul>
        <% @article.errors.full_messages.each do |msg| %>
          <li><%= msg %></li>
        <% end %>
      </ul>
    </div>
  <% end %>

  <p>
    <%= form.label :title %><br>
    <%= form.text_field :title %>
  </p>

  <p>
    <%= form.label :text %><br>
    <%= form.text_area :text %>
  </p>

  <p>
    <%= form.submit %>
  </p>

<% end %>

<%= link_to 'Back', articles_path %>
```

A few things are going on. We check if there are any errors with
`@article.errors.any?`, and in that case we show a list of all
errors with `@article.errors.full_messages`.

`pluralize` is a rails helper that takes a number and a string as its
arguments. If the number is greater than one, the string will be automatically
pluralized.

The reason why we added `@article = Article.new` in the `ArticlesController` is
that otherwise `@article` would be `nil` in our view, and calling
`@article.errors.any?` would throw an error.

TIP: Rails automatically wraps fields that contain an error with a div
with class `field_with_errors`. You can define a CSS rule to make them
standout.

Now you'll get a nice error message when saving an article without a title when
you attempt to do just that on the new article form
<http://localhost:3000/articles/new>:

![Form With Errors](images/getting_started/form_with_errors.png)

### Updating Articles

We've covered the "CR" part of CRUD. Now let's focus on the "U" part, updating
articles.

The first step we'll take is adding an `edit` action to the `ArticlesController`,
generally between the `new` and `create` actions, as shown:

```ruby
def new
  @article = Article.new
end

def edit
  @article = Article.find(params[:id])
end

def create
  @article = Article.new(article_params)

  if @article.save
    redirect_to @article
  else
    render 'new'
  end
end
```

The view will contain a form similar to the one we used when creating
new articles. Create a file called `app/views/articles/edit.html.erb` and make
it look as follows:

```html+erb
<h1>Edit article</h1>

<%= form_with(model: @article, local: true) do |form| %>

  <% if @article.errors.any? %>
    <div id="error_explanation">
      <h2>
        <%= pluralize(@article.errors.count, "error") %> prohibited
        this article from being saved:
      </h2>
      <ul>
        <% @article.errors.full_messages.each do |msg| %>
          <li><%= msg %></li>
        <% end %>
      </ul>
    </div>
  <% end %>

  <p>
    <%= form.label :title %><br>
    <%= form.text_field :title %>
  </p>

  <p>
    <%= form.label :text %><br>
    <%= form.text_area :text %>
  </p>

  <p>
    <%= form.submit %>
  </p>

<% end %>

<%= link_to 'Back', articles_path %>
```

This time we point the form to the `update` action, which is not defined yet
but will be very soon.

Passing the article object to the `form_with` method will automatically set the URL for
submitting the edited article form. This option tells Rails that we want this
form to be submitted via the `PATCH` HTTP method, which is the HTTP method you're
expected to use to **update** resources according to the REST protocol.

Also, passing a model object to `form_with`, like `model: @article` in the edit
view above, will cause form helpers to fill in form fields with the corresponding
values of the object.  Passing in a symbol scope such as `scope: :article`, as
was done in the new view, only creates empty form fields.
More details can be found in [form_with documentation]
(http://api.rubyonrails.org/classes/ActionView/Helpers/FormHelper.html#method-i-form_with).

Next, we need to create the `update` action in
`app/controllers/articles_controller.rb`.
Add it between the `create` action and the `private` method:

```ruby
def create
  @article = Article.new(article_params)

  if @article.save
    redirect_to @article
  else
    render 'new'
  end
end

def update
  @article = Article.find(params[:id])

  if @article.update(article_params)
    redirect_to @article
  else
    render 'edit'
  end
end

private
  def article_params
    params.require(:article).permit(:title, :text)
  end
```

The new method, `update`, is used when you want to update a record
that already exists, and it accepts a hash containing the attributes
that you want to update. As before, if there was an error updating the
article we want to show the form back to the user.

We reuse the `article_params` method that we defined earlier for the create
action.

TIP: It is not necessary to pass all the attributes to `update`. For example,
if `@article.update(title: 'A new title')` was called, Rails would only update
the `title` attribute, leaving all other attributes untouched.

Finally, we want to show a link to the `edit` action in the list of all the
articles, so let's add that now to `app/views/articles/index.html.erb` to make
it appear next to the "Show" link:

```html+erb
<table>
  <tr>
    <th>Title</th>
    <th>Text</th>
    <th colspan="2"></th>
  </tr>

  <% @articles.each do |article| %>
    <tr>
      <td><%= article.title %></td>
      <td><%= article.text %></td>
      <td><%= link_to 'Show', article_path(article) %></td>
      <td><%= link_to 'Edit', edit_article_path(article) %></td>
    </tr>
  <% end %>
</table>
```

And we'll also add one to the `app/views/articles/show.html.erb` template as
well, so that there's also an "Edit" link on an article's page. Add this at the
bottom of the template:

```html+erb
...

<%= link_to 'Edit', edit_article_path(@article) %> |
<%= link_to 'Back', articles_path %>
```

And here's how our app looks so far:

![Index action with edit link](images/getting_started/index_action_with_edit_link.png)

### Using partials to clean up duplication in views

Our `edit` page looks very similar to the `new` page; in fact, they
both share the same code for displaying the form. Let's remove this
duplication by using a view partial. By convention, partial files are
prefixed with an underscore.

TIP: You can read more about partials in the
[Layouts and Rendering in Rails](layouts_and_rendering.html) guide.

Create a new file `app/views/articles/_form.html.erb` with the following
content:

```html+erb
<%= form_with model: @article, local: true do |form| %>

  <% if @article.errors.any? %>
    <div id="error_explanation">
      <h2>
        <%= pluralize(@article.errors.count, "error") %> prohibited
        this article from being saved:
      </h2>
      <ul>
        <% @article.errors.full_messages.each do |msg| %>
          <li><%= msg %></li>
        <% end %>
      </ul>
    </div>
  <% end %>

  <p>
    <%= form.label :title %><br>
    <%= form.text_field :title %>
  </p>

  <p>
    <%= form.label :text %><br>
    <%= form.text_area :text %>
  </p>

  <p>
    <%= form.submit %>
  </p>

<% end %>
```

Everything except for the `form_with` declaration remained the same.
The reason we can use this shorter, simpler `form_with` declaration
to stand in for either of the other forms is that `@article` is a *resource*
corresponding to a full set of RESTful routes, and Rails is able to infer
which URI and method to use.
For more information about this use of `form_with`, see [Resource-oriented style]
(http://api.rubyonrails.org/classes/ActionView/Helpers/FormHelper.html#method-i-form_with-label-Resource-oriented+style).

Now, let's update the `app/views/articles/new.html.erb` view to use this new
partial, rewriting it completely:

```html+erb
<h1>New article</h1>

<%= render 'form' %>

<%= link_to 'Back', articles_path %>
```

Then do the same for the `app/views/articles/edit.html.erb` view:

```html+erb
<h1>Edit article</h1>

<%= render 'form' %>

<%= link_to 'Back', articles_path %>
```

### Deleting Articles

We're now ready to cover the "D" part of CRUD, deleting articles from the
database. Following the REST convention, the route for
deleting articles as per output of `rails routes` is:

```ruby
DELETE /articles/:id(.:format)      articles#destroy
```

The `delete` routing method should be used for routes that destroy
resources. If this was left as a typical `get` route, it could be possible for
people to craft malicious URLs like this:

```html
<a href='http://example.com/articles/1/destroy'>look at this cat!</a>
```

We use the `delete` method for destroying resources, and this route is mapped
to the `destroy` action inside `app/controllers/articles_controller.rb`, which
doesn't exist yet. The `destroy` method is generally the last CRUD action in
the controller, and like the other public CRUD actions, it must be placed
before any `private` or `protected` methods. Let's add it:

```ruby
def destroy
  @article = Article.find(params[:id])
  @article.destroy

  redirect_to articles_path
end
```

The complete `ArticlesController` in the
`app/controllers/articles_controller.rb` file should now look like this:

```ruby
class ArticlesController < ApplicationController
  def index
    @articles = Article.all
  end

  def show
    @article = Article.find(params[:id])
  end

  def new
    @article = Article.new
  end

  def edit
    @article = Article.find(params[:id])
  end

  def create
    @article = Article.new(article_params)

    if @article.save
      redirect_to @article
    else
      render 'new'
    end
  end

  def update
    @article = Article.find(params[:id])

    if @article.update(article_params)
      redirect_to @article
    else
      render 'edit'
    end
  end

  def destroy
    @article = Article.find(params[:id])
    @article.destroy

    redirect_to articles_path
  end

  private
    def article_params
      params.require(:article).permit(:title, :text)
    end
end
```

You can call `destroy` on Active Record objects when you want to delete
them from the database. Note that we don't need to add a view for this
action since we're redirecting to the `index` action.

Finally, add a 'Destroy' link to your `index` action template
(`app/views/articles/index.html.erb`) to wrap everything together.

```html+erb
<h1>Listing Articles</h1>
<%= link_to 'New article', new_article_path %>
<table>
  <tr>
    <th>Title</th>
    <th>Text</th>
    <th colspan="3"></th>
  </tr>

  <% @articles.each do |article| %>
    <tr>
      <td><%= article.title %></td>
      <td><%= article.text %></td>
      <td><%= link_to 'Show', article_path(article) %></td>
      <td><%= link_to 'Edit', edit_article_path(article) %></td>
      <td><%= link_to 'Destroy', article_path(article),
              method: :delete,
              data: { confirm: 'Are you sure?' } %></td>
    </tr>
  <% end %>
</table>
```

Here we're using `link_to` in a different way. We pass the named route as the
second argument, and then the options as another argument. The `method: :delete`
and `data: { confirm: 'Are you sure?' }` options are used as HTML5 attributes so
that when the link is clicked, Rails will first show a confirm dialog to the
user, and then submit the link with method `delete`.  This is done via the
JavaScript file `rails-ujs` which is automatically included in your
application's layout (`app/views/layouts/application.html.erb`) when you
generated the application. Without this file, the confirmation dialog box won't
appear.

![Confirm Dialog](images/getting_started/confirm_dialog.png)

TIP: Learn more about Unobtrusive JavaScript on
[Working With JavaScript in Rails](working_with_javascript_in_rails.html) guide.

Congratulations, you can now create, show, list, update, and destroy
articles.

TIP: In general, Rails encourages using resources objects instead of
declaring routes manually. For more information about routing, see
[Rails Routing from the Outside In](routing.html).

Adding a Second Model
---------------------

It's time to add a second model to the application. The second model will handle
comments on articles.

### Generating a Model

We're going to see the same generator that we used before when creating
the `Article` model. This time we'll create a `Comment` model to hold a
reference to an article. Run this command in your terminal:

```bash
$ rails generate model Comment commenter:string body:text article:references
```

This command will generate four files:

| File                                         | Purpose                                                                                                |
| -------------------------------------------- | ------------------------------------------------------------------------------------------------------ |
| db/migrate/20140120201010_create_comments.rb | Migration to create the comments table in your database (your name will include a different timestamp) |
| app/models/comment.rb                        | The Comment model                                                                                      |
| test/models/comment_test.rb                  | Testing harness for the comment model                                                                 |
| test/fixtures/comments.yml                   | Sample comments for use in testing                                                                     |

First, take a look at `app/models/comment.rb`:

```ruby
class Comment < ApplicationRecord
  belongs_to :article
end
```

This is very similar to the `Article` model that you saw earlier. The difference
is the line `belongs_to :article`, which sets up an Active Record _association_.
You'll learn a little about associations in the next section of this guide.

The (`:references`) keyword used in the bash command is a special data type for models.
It creates a new column on your database table with the provided model name appended with an `_id`
that can hold integer values. To get a better understanding, analyze the
`db/schema.rb` file after running the migration.

In addition to the model, Rails has also made a migration to create the
corresponding database table:

```ruby
class CreateComments < ActiveRecord::Migration[5.0]
  def change
    create_table :comments do |t|
      t.string :commenter
      t.text :body
      t.references :article, foreign_key: true

      t.timestamps
    end
  end
end
```

The `t.references` line creates an integer column called `article_id`, an index
for it, and a foreign key constraint that points to the `id` column of the `articles`
table. Go ahead and run the migration:

```bash
$ rails db:migrate
```

Rails is smart enough to only execute the migrations that have not already been
run against the current database, so in this case you will just see:

```bash
==  CreateComments: migrating =================================================
-- create_table(:comments)
   -> 0.0115s
==  CreateComments: migrated (0.0119s) ========================================
```

### Associating Models

Active Record associations let you easily declare the relationship between two
models. In the case of comments and articles, you could write out the
relationships this way:

* Each comment belongs to one article.
* One article can have many comments.

In fact, this is very close to the syntax that Rails uses to declare this
association. You've already seen the line of code inside the `Comment` model
(app/models/comment.rb) that makes each comment belong to an Article:

```ruby
class Comment < ApplicationRecord
  belongs_to :article
end
```

You'll need to edit `app/models/article.rb` to add the other side of the
association:

```ruby
class Article < ApplicationRecord
  has_many :comments
  validates :title, presence: true,
                    length: { minimum: 5 }
end
```

These two declarations enable a good bit of automatic behavior. For example, if
you have an instance variable `@article` containing an article, you can retrieve
all the comments belonging to that article as an array using
`@article.comments`.

TIP: For more information on Active Record associations, see the [Active Record
Associations](association_basics.html) guide.

### Adding a Route for Comments

As with the `welcome` controller, we will need to add a route so that Rails
knows where we would like to navigate to see `comments`. Open up the
`config/routes.rb` file again, and edit it as follows:

```ruby
resources :articles do
  resources :comments
end
```

This creates `comments` as a _nested resource_ within `articles`. This is
another part of capturing the hierarchical relationship that exists between
articles and comments.

TIP: For more information on routing, see the [Rails Routing](routing.html)
guide.

### Generating a Controller

With the model in hand, you can turn your attention to creating a matching
controller. Again, we'll use the same generator we used before:

```bash
$ rails generate controller Comments
```

This creates five files and one empty directory:

| File/Directory                               | Purpose                                  |
| -------------------------------------------- | ---------------------------------------- |
| app/controllers/comments_controller.rb       | The Comments controller                  |
| app/views/comments/                          | Views of the controller are stored here  |
| test/controllers/comments_controller_test.rb | The test for the controller              |
| app/helpers/comments_helper.rb               | A view helper file                       |
| app/assets/javascripts/comments.coffee       | CoffeeScript for the controller          |
| app/assets/stylesheets/comments.scss         | Cascading style sheet for the controller |

Like with any blog, our readers will create their comments directly after
reading the article, and once they have added their comment, will be sent back
to the article show page to see their comment now listed. Due to this, our
`CommentsController` is there to provide a method to create comments and delete
spam comments when they arrive.

So first, we'll wire up the Article show template
(`app/views/articles/show.html.erb`) to let us make a new comment:

```html+erb
<p>
  <strong>Title:</strong>
  <%= @article.title %>
</p>

<p>
  <strong>Text:</strong>
  <%= @article.text %>
</p>

<h2>Add a comment:</h2>
<%= form_with(model: [ @article, @article.comments.build ], local: true) do |form| %>
  <p>
    <%= form.label :commenter %><br>
    <%= form.text_field :commenter %>
  </p>
  <p>
    <%= form.label :body %><br>
    <%= form.text_area :body %>
  </p>
  <p>
    <%= form.submit %>
  </p>
<% end %>

<%= link_to 'Edit', edit_article_path(@article) %> |
<%= link_to 'Back', articles_path %>
```

This adds a form on the `Article` show page that creates a new comment by
calling the `CommentsController` `create` action. The `form_with` call here uses
an array, which will build a nested route, such as `/articles/1/comments`.

Let's wire up the `create` in `app/controllers/comments_controller.rb`:

```ruby
class CommentsController < ApplicationController
  def create
    @article = Article.find(params[:article_id])
    @comment = @article.comments.create(comment_params)
    redirect_to article_path(@article)
  end

  private
    def comment_params
      params.require(:comment).permit(:commenter, :body)
    end
end
```

You'll see a bit more complexity here than you did in the controller for
articles. That's a side-effect of the nesting that you've set up. Each request
for a comment has to keep track of the article to which the comment is attached,
thus the initial call to the `find` method of the `Article` model to get the
article in question.

In addition, the code takes advantage of some of the methods available for an
association. We use the `create` method on `@article.comments` to create and
save the comment. This will automatically link the comment so that it belongs to
that particular article.

Once we have made the new comment, we send the user back to the original article
using the `article_path(@article)` helper. As we have already seen, this calls
the `show` action of the `ArticlesController` which in turn renders the
`show.html.erb` template. This is where we want the comment to show, so let's
add that to the `app/views/articles/show.html.erb`.

```html+erb
<p>
  <strong>Title:</strong>
  <%= @article.title %>
</p>

<p>
  <strong>Text:</strong>
  <%= @article.text %>
</p>

<h2>Comments</h2>
<% @article.comments.each do |comment| %>
  <p>
    <strong>Commenter:</strong>
    <%= comment.commenter %>
  </p>

  <p>
    <strong>Comment:</strong>
    <%= comment.body %>
  </p>
<% end %>

<h2>Add a comment:</h2>
<%= form_with(model: [ @article, @article.comments.build ], local: true) do |form| %>
  <p>
    <%= form.label :commenter %><br>
    <%= form.text_field :commenter %>
  </p>
  <p>
    <%= form.label :body %><br>
    <%= form.text_area :body %>
  </p>
  <p>
    <%= form.submit %>
  </p>
<% end %>

<%= link_to 'Edit', edit_article_path(@article) %> |
<%= link_to 'Back', articles_path %>
```

Now you can add articles and comments to your blog and have them show up in the
right places.

![Article with Comments](images/getting_started/article_with_comments.png)

Refactoring
-----------

Now that we have articles and comments working, take a look at the
`app/views/articles/show.html.erb` template. It is getting long and awkward. We
can use partials to clean it up.

### Rendering Partial Collections

First, we will make a comment partial to extract showing all the comments for
the article. Create the file `app/views/comments/_comment.html.erb` and put the
following into it:

```html+erb
<p>
  <strong>Commenter:</strong>
  <%= comment.commenter %>
</p>

<p>
  <strong>Comment:</strong>
  <%= comment.body %>
</p>
```

Then you can change `app/views/articles/show.html.erb` to look like the
following:

```html+erb
<p>
  <strong>Title:</strong>
  <%= @article.title %>
</p>

<p>
  <strong>Text:</strong>
  <%= @article.text %>
</p>

<h2>Comments</h2>
<%= render @article.comments %>

<h2>Add a comment:</h2>
<%= form_with(model: [ @article, @article.comments.build ], local: true) do |form| %>
  <p>
    <%= form.label :commenter %><br>
    <%= form.text_field :commenter %>
  </p>
  <p>
    <%= form.label :body %><br>
    <%= form.text_area :body %>
  </p>
  <p>
    <%= form.submit %>
  </p>
<% end %>

<%= link_to 'Edit', edit_article_path(@article) %> |
<%= link_to 'Back', articles_path %>
```

This will now render the partial in `app/views/comments/_comment.html.erb` once
for each comment that is in the `@article.comments` collection. As the `render`
method iterates over the `@article.comments` collection, it assigns each
comment to a local variable named the same as the partial, in this case
`comment`, which is then available in the partial for us to show.

### Rendering a Partial Form

Let us also move that new comment section out to its own partial. Again, you
create a file `app/views/comments/_form.html.erb` containing:

```html+erb
<%= form_with(model: [ @article, @article.comments.build ], local: true) do |form| %>
  <p>
    <%= form.label :commenter %><br>
    <%= form.text_field :commenter %>
  </p>
  <p>
    <%= form.label :body %><br>
    <%= form.text_area :body %>
  </p>
  <p>
    <%= form.submit %>
  </p>
<% end %>
```

Then you make the `app/views/articles/show.html.erb` look like the following:

```html+erb
<p>
  <strong>Title:</strong>
  <%= @article.title %>
</p>

<p>
  <strong>Text:</strong>
  <%= @article.text %>
</p>

<h2>Comments</h2>
<%= render @article.comments %>

<h2>Add a comment:</h2>
<%= render 'comments/form' %>

<%= link_to 'Edit', edit_article_path(@article) %> |
<%= link_to 'Back', articles_path %>
```

The second render just defines the partial template we want to render,
`comments/form`. Rails is smart enough to spot the forward slash in that
string and realize that you want to render the `_form.html.erb` file in
the `app/views/comments` directory.

The `@article` object is available to any partials rendered in the view because
we defined it as an instance variable.

Deleting Comments
-----------------

Another important feature of a blog is being able to delete spam comments. To do
this, we need to implement a link of some sort in the view and a `destroy`
action in the `CommentsController`.

So first, let's add the delete link in the
`app/views/comments/_comment.html.erb` partial:

```html+erb
<p>
  <strong>Commenter:</strong>
  <%= comment.commenter %>
</p>

<p>
  <strong>Comment:</strong>
  <%= comment.body %>
</p>

<p>
  <%= link_to 'Destroy Comment', [comment.article, comment],
               method: :delete,
               data: { confirm: 'Are you sure?' } %>
</p>
```

Clicking this new "Destroy Comment" link will fire off a `DELETE
/articles/:article_id/comments/:id` to our `CommentsController`, which can then
use this to find the comment we want to delete, so let's add a `destroy` action
to our controller (`app/controllers/comments_controller.rb`):

```ruby
class CommentsController < ApplicationController
  def create
    @article = Article.find(params[:article_id])
    @comment = @article.comments.create(comment_params)
    redirect_to article_path(@article)
  end

  def destroy
    @article = Article.find(params[:article_id])
    @comment = @article.comments.find(params[:id])
    @comment.destroy
    redirect_to article_path(@article)
  end

  private
    def comment_params
      params.require(:comment).permit(:commenter, :body)
    end
end
```

The `destroy` action will find the article we are looking at, locate the comment
within the `@article.comments` collection, and then remove it from the
database and send us back to the show action for the article.


### Deleting Associated Objects

If you delete an article, its associated comments will also need to be
deleted, otherwise they would simply occupy space in the database. Rails allows
you to use the `dependent` option of an association to achieve this. Modify the
Article model, `app/models/article.rb`, as follows:

```ruby
class Article < ApplicationRecord
  has_many :comments, dependent: :destroy
  validates :title, presence: true,
                    length: { minimum: 5 }
end
```

Security
--------

### Basic Authentication

If you were to publish your blog online, anyone would be able to add, edit and
delete articles or delete comments.

Rails provides a very simple HTTP authentication system that will work nicely in
this situation.

In the `ArticlesController` we need to have a way to block access to the
various actions if the person is not authenticated. Here we can use the Rails
`http_basic_authenticate_with` method, which allows access to the requested
action if that method allows it.

To use the authentication system, we specify it at the top of our
`ArticlesController` in `app/controllers/articles_controller.rb`. In our case,
we want the user to be authenticated on every action except `index` and `show`,
so we write that:

```ruby
class ArticlesController < ApplicationController

  http_basic_authenticate_with name: "dhh", password: "secret", except: [:index, :show]

  def index
    @articles = Article.all
  end

  # snippet for brevity
```

We also want to allow only authenticated users to delete comments, so in the
`CommentsController` (`app/controllers/comments_controller.rb`) we write:

```ruby
class CommentsController < ApplicationController

  http_basic_authenticate_with name: "dhh", password: "secret", only: :destroy

  def create
    @article = Article.find(params[:article_id])
    # ...
  end

  # snippet for brevity
```

Now if you try to create a new article, you will be greeted with a basic HTTP
Authentication challenge:

![Basic HTTP Authentication Challenge](images/getting_started/challenge.png)

Other authentication methods are available for Rails applications. Two popular
authentication add-ons for Rails are the
[Devise](https://github.com/plataformatec/devise) rails engine and
the [Authlogic](https://github.com/binarylogic/authlogic) gem,
along with a number of others.


### Other Security Considerations

Security, especially in web applications, is a broad and detailed area. Security
in your Rails application is covered in more depth in
the [Ruby on Rails Security Guide](security.html).


What's Next?
------------

Now that you've seen your first Rails application, you should feel free to
update it and experiment on your own.

Remember, you don't have to do everything without help. As you need assistance
getting up and running with Rails, feel free to consult these support
resources:

* The [Ruby on Rails Guides](index.html)
* The [Ruby on Rails Tutorial](https://www.railstutorial.org/book)
* The [Ruby on Rails mailing list](https://groups.google.com/group/rubyonrails-talk)
* The [#rubyonrails](irc://irc.freenode.net/#rubyonrails) channel on irc.freenode.net


Configuration Gotchas
---------------------

The easiest way to work with Rails is to store all external data as UTF-8. If
you don't, Ruby libraries and Rails will often be able to convert your native
data into UTF-8, but this doesn't always work reliably, so you're better off
ensuring that all external data is UTF-8.

If you have made a mistake in this area, the most common symptom is a black
diamond with a question mark inside appearing in the browser. Another common
symptom is characters like "ü" appearing instead of "ü". Rails takes a number
of internal steps to mitigate common causes of these problems that can be
automatically detected and corrected. However, if you have external data that is
not stored as UTF-8, it can occasionally result in these kinds of issues that
cannot be automatically detected by Rails and corrected.

Two very common sources of data that are not UTF-8:

* Your text editor: Most text editors (such as TextMate), default to saving
  files as UTF-8. If your text editor does not, this can result in special
  characters that you enter in your templates (such as é) to appear as a diamond
  with a question mark inside in the browser. This also applies to your i18n
  translation files. Most editors that do not already default to UTF-8 (such as
  some versions of Dreamweaver) offer a way to change the default to UTF-8. Do
  so.
* Your database: Rails defaults to converting data from your database into UTF-8
  at the boundary. However, if your database is not using UTF-8 internally, it
  may not be able to store all characters that your users enter. For instance,
  if your database is using Latin-1 internally, and your user enters a Russian,
  Hebrew, or Japanese character, the data will be lost forever once it enters
  the database. If possible, use UTF-8 as the internal storage of your database.