diff options
Diffstat (limited to 'guides/source/active_record_basics.md')
| -rw-r--r-- | guides/source/active_record_basics.md | 42 |
1 files changed, 28 insertions, 14 deletions
diff --git a/guides/source/active_record_basics.md b/guides/source/active_record_basics.md index 6b3aa471f9..fad4c19827 100644 --- a/guides/source/active_record_basics.md +++ b/guides/source/active_record_basics.md @@ -1,4 +1,4 @@ -**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON http://guides.rubyonrails.org.** +**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON https://guides.rubyonrails.org.** Active Record Basics ==================== @@ -13,14 +13,14 @@ After reading this guide, you will know: * How to use Active Record models to manipulate data stored in a relational database. * Active Record schema naming conventions. -* The concepts of database migrations, validations and callbacks. +* The concepts of database migrations, validations, and callbacks. -------------------------------------------------------------------------------- What is Active Record? ---------------------- -Active Record is the M in [MVC](http://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller) - the +Active Record is the M in [MVC](https://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller) - the model - which is the layer of the system responsible for representing business data and logic. Active Record facilitates the creation and use of business objects whose data requires persistent storage to a database. It is an @@ -38,13 +38,15 @@ object on how to write to and read from the database. ### Object Relational Mapping -Object Relational Mapping, commonly referred to as its abbreviation ORM, is +[Object Relational Mapping](https://en.wikipedia.org/wiki/Object-relational_mapping), commonly referred to as its abbreviation ORM, is a technique that connects the rich objects of an application to tables in a relational database management system. Using ORM, the properties and relationships of the objects in an application can be easily stored and retrieved from a database without writing SQL statements directly and with less overall database access code. +NOTE: If you are not familiar enough with relational database management systems (RDBMS) or structured query language (SQL), please go through [this tutorial](https://www.w3schools.com/sql/default.asp) (or [this one](http://www.sqlcourse.com/)) or study them by other means. Understanding how relational databases work is crucial to understanding Active Records and Rails in general. + ### Active Record as an ORM Framework Active Record gives us several mechanisms, the most important being the ability @@ -113,7 +115,7 @@ to Active Record instances: * `created_at` - Automatically gets set to the current date and time when the record is first created. * `updated_at` - Automatically gets set to the current date and time whenever - the record is updated. + the record is created or updated. * `lock_version` - Adds [optimistic locking](http://api.rubyonrails.org/classes/ActiveRecord/Locking.html) to a model. @@ -142,7 +144,7 @@ end This will create a `Product` model, mapped to a `products` table at the database. By doing this you'll also have the ability to map the columns of each row in that table with the attributes of the instances of your model. Suppose -that the `products` table was created using an SQL statement like: +that the `products` table was created using an SQL (or one of its extensions) statement like: ```sql CREATE TABLE products ( @@ -152,8 +154,9 @@ CREATE TABLE products ( ); ``` -Following the table schema above, you would be able to write code like the -following: +Schema above declares a table with two columns: `id` and `name`. Each row of +this table represents a certain product with these two parameters. Thus, you +would be able to write code like the following: ```ruby p = Product.new @@ -208,7 +211,7 @@ to allow an application to read and manipulate data stored within its tables. ### Create -Active Record objects can be created from a hash, a block or have their +Active Record objects can be created from a hash, a block, or have their attributes manually set after creation. The `new` method will return a new object while `create` will return the object and save it to the database. @@ -304,18 +307,29 @@ user = User.find_by(name: 'David') user.destroy ``` +If you'd like to delete several records in bulk, you may use `destroy_all` +method: + +```ruby +# find and delete all users named David +User.where(name: 'David').destroy_all + +# delete all users +User.destroy_all +``` + Validations ----------- Active Record allows you to validate the state of a model before it gets written into the database. There are several methods that you can use to check your models and validate that an attribute value is not empty, is unique and not -already in the database, follows a specific format and many more. +already in the database, follows a specific format, and many more. Validation is a very important issue to consider when persisting to the database, so the methods `save` and `update` take it into account when -running: they return `false` when validation fails and they didn't actually -perform any operation on the database. All of these have a bang counterpart (that +running: they return `false` when validation fails and they don't actually +perform any operations on the database. All of these have a bang counterpart (that is, `save!` and `update!`), which are stricter in that they raise the exception `ActiveRecord::RecordInvalid` if validation fails. A quick example to illustrate: @@ -339,7 +353,7 @@ Callbacks Active Record callbacks allow you to attach code to certain events in the life-cycle of your models. This enables you to add behavior to your models by transparently executing code when those events occur, like when you create a new -record, update it, destroy it and so on. You can learn more about callbacks in +record, update it, destroy it, and so on. You can learn more about callbacks in the [Active Record Callbacks guide](active_record_callbacks.html). Migrations @@ -373,5 +387,5 @@ provides rollback features. To actually create the table, you'd run `rails db:mi and to roll it back, `rails db:rollback`. Note that the above code is database-agnostic: it will run in MySQL, -PostgreSQL, Oracle and others. You can learn more about migrations in the +PostgreSQL, Oracle, and others. You can learn more about migrations in the [Active Record Migrations guide](active_record_migrations.html). |