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author | Mingdong Luo <mdluo@nsmss.com> | 2015-01-31 19:23:48 -0800 |
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committer | Mingdong Luo <mdluo@nsmss.com> | 2015-01-31 19:23:48 -0800 |
commit | 549d171a90135999e3c670f489494b7a39dd6dd7 (patch) | |
tree | 233466527b797fe3ea7c6a7a3673795cea28aebe /guides/source/active_record_migrations.md | |
parent | c840b18ac31a852d99ff760229f2c087b6961727 (diff) | |
parent | 70ac072976c8cc6f013f0df3777e54ccae3f4f8c (diff) | |
download | rails-549d171a90135999e3c670f489494b7a39dd6dd7.tar.gz rails-549d171a90135999e3c670f489494b7a39dd6dd7.tar.bz2 rails-549d171a90135999e3c670f489494b7a39dd6dd7.zip |
Merge branch 'master' into pr/18316
Conflicts:
activerecord/CHANGELOG.md
Diffstat (limited to 'guides/source/active_record_migrations.md')
-rw-r--r-- | guides/source/active_record_migrations.md | 17 |
1 files changed, 11 insertions, 6 deletions
diff --git a/guides/source/active_record_migrations.md b/guides/source/active_record_migrations.md index 8ae282bad2..b8db21a989 100644 --- a/guides/source/active_record_migrations.md +++ b/guides/source/active_record_migrations.md @@ -1,4 +1,4 @@ -**DO NOT READ THIS FILE IN GITHUB, GUIDES ARE PUBLISHED IN http://guides.rubyonrails.org.** +**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON http://guides.rubyonrails.org.** Active Record Migrations ======================== @@ -479,7 +479,8 @@ Rails will generate a name for every foreign key starting with There is a `:name` option to specify a different name if needed. NOTE: Active Record only supports single column foreign keys. `execute` and -`structure.sql` are required to use composite foreign keys. +`structure.sql` are required to use composite foreign keys. See +[Schema Dumping and You](#schema-dumping-and-you). Removing a foreign key is easy as well: @@ -695,6 +696,10 @@ of `create_table` and `reversible`, replacing `create_table` by `drop_table`, and finally replacing `up` by `down` and vice-versa. This is all taken care of by `revert`. +NOTE: If you want to add check constraints like in the examples above, +you will have to use `structure.sql` as dump method. See +[Schema Dumping and You](#schema-dumping-and-you). + Running Migrations ------------------ @@ -943,10 +948,10 @@ that Active Record supports. This could be very useful if you were to distribute an application that is able to run against multiple databases. There is however a trade-off: `db/schema.rb` cannot express database specific -items such as triggers, or stored procedures. While in a migration you can -execute custom SQL statements, the schema dumper cannot reconstitute those -statements from the database. If you are using features like this, then you -should set the schema format to `:sql`. +items such as triggers, stored procedures or check constraints. While in a +migration you can execute custom SQL statements, the schema dumper cannot +reconstitute those statements from the database. If you are using features like +this, then you should set the schema format to `:sql`. Instead of using Active Record's schema dumper, the database's structure will be dumped using a tool specific to the database (via the `db:structure:dump` |