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diff --git a/guides/source/active_record_querying.md b/guides/source/active_record_querying.md index ec31fa9d67..af15d4870c 100644 --- a/guides/source/active_record_querying.md +++ b/guides/source/active_record_querying.md @@ -11,7 +11,7 @@ After reading this guide, you will know: * How to specify the order, retrieved attributes, grouping, and other properties of the found records. * How to use eager loading to reduce the number of database queries needed for data retrieval. * How to use dynamic finder methods. -* How to use method chaining to use multiple ActiveRecord methods together. +* How to use method chaining to use multiple Active Record methods together. * How to check for the existence of particular records. * How to perform various calculations on Active Record models. * How to run EXPLAIN on relations. @@ -25,7 +25,7 @@ Code examples throughout this guide will refer to one or more of the following m TIP: All of the following models use `id` as the primary key, unless specified otherwise. ```ruby -class Client < ActiveRecord::Base +class Client < ApplicationRecord has_one :address has_many :orders has_and_belongs_to_many :roles @@ -33,19 +33,19 @@ end ``` ```ruby -class Address < ActiveRecord::Base +class Address < ApplicationRecord belongs_to :client end ``` ```ruby -class Order < ActiveRecord::Base +class Order < ApplicationRecord belongs_to :client, counter_cache: true end ``` ```ruby -class Role < ActiveRecord::Base +class Role < ApplicationRecord has_and_belongs_to_many :clients end ``` @@ -59,7 +59,7 @@ To retrieve objects from the database, Active Record provides several finder met The methods are: -* `bind` +* `find` * `create_with` * `distinct` * `eager_load` @@ -170,7 +170,7 @@ TIP: The retrieved record may vary depending on the database engine. #### `first` -The `first` method finds the first record ordered by the primary key. For example: +The `first` method finds the first record ordered by primary key (default). For example: ```ruby client = Client.first @@ -204,11 +204,24 @@ The SQL equivalent of the above is: SELECT * FROM clients ORDER BY clients.id ASC LIMIT 3 ``` +On a collection that is ordered using `order`, `first` will return the first record ordered by the specified attribute for `order`. + +```ruby +client = Client.order(:first_name).first +# => #<Client id: 2, first_name: "Fifo"> +``` + +The SQL equivalent of the above is: + +```sql +SELECT * FROM clients ORDER BY clients.first_name ASC LIMIT 1 +``` + The `first!` method behaves exactly like `first`, except that it will raise `ActiveRecord::RecordNotFound` if no matching record is found. #### `last` -The `last` method finds the last record ordered by the primary key. For example: +The `last` method finds the last record ordered by primary key (default). For example: ```ruby client = Client.last @@ -242,6 +255,19 @@ The SQL equivalent of the above is: SELECT * FROM clients ORDER BY clients.id DESC LIMIT 3 ``` +On a collection that is ordered using `order`, `last` will return the last record ordered by the specified attribute for `order`. + +```ruby +client = Client.order(:first_name).last +# => #<Client id: 220, first_name: "Sara"> +``` + +The SQL equivalent of the above is: + +```sql +SELECT * FROM clients ORDER BY clients.first_name DESC LIMIT 1 +``` + The `last!` method behaves exactly like `last`, except that it will raise `ActiveRecord::RecordNotFound` if no matching record is found. #### `find_by` @@ -322,7 +348,7 @@ end The `find_each` method accepts most of the options allowed by the regular `find` method, except for `:order` and `:limit`, which are reserved for internal use by `find_each`. -Three additional options, `:batch_size`, `:begin_at` and `:end_at`, are available as well. +Three additional options, `:batch_size`, `:start` and `:finish`, are available as well. **`:batch_size`** @@ -334,34 +360,34 @@ User.find_each(batch_size: 5000) do |user| end ``` -**`:begin_at`** +**`:start`** -By default, records are fetched in ascending order of the primary key, which must be an integer. The `:begin_at` option allows you to configure the first ID of the sequence whenever the lowest ID is not the one you need. This would be useful, for example, if you wanted to resume an interrupted batch process, provided you saved the last processed ID as a checkpoint. +By default, records are fetched in ascending order of the primary key, which must be an integer. The `:start` option allows you to configure the first ID of the sequence whenever the lowest ID is not the one you need. This would be useful, for example, if you wanted to resume an interrupted batch process, provided you saved the last processed ID as a checkpoint. For example, to send newsletters only to users with the primary key starting from 2000, and to retrieve them in batches of 5000: ```ruby -User.find_each(begin_at: 2000, batch_size: 5000) do |user| +User.find_each(start: 2000, batch_size: 5000) do |user| NewsMailer.weekly(user).deliver_now end ``` -**`:end_at`** +**`:finish`** -Similar to the `:begin_at` option, `:end_at` allows you to configure the last ID of the sequence whenever the highest ID is not the one you need. -This would be useful, for example, if you wanted to run a batch process, using a subset of records based on `:begin_at` and `:end_at` +Similar to the `:start` option, `:finish` allows you to configure the last ID of the sequence whenever the highest ID is not the one you need. +This would be useful, for example, if you wanted to run a batch process, using a subset of records based on `:start` and `:finish` For example, to send newsletters only to users with the primary key starting from 2000 up to 10000 and to retrieve them in batches of 5000: ```ruby -User.find_each(begin_at: 2000, end_at: 10000, batch_size: 5000) do |user| +User.find_each(start: 2000, finish: 10000, batch_size: 5000) do |user| NewsMailer.weekly(user).deliver_now end ``` Another example would be if you wanted multiple workers handling the same processing queue. You could have each worker handle 10000 records by setting the -appropriate `:begin_at` and `:end_at` options on each worker. +appropriate `:start` and `:finish` options on each worker. #### `find_in_batches` @@ -376,7 +402,7 @@ end ##### Options for `find_in_batches` -The `find_in_batches` method accepts the same `:batch_size`, `:begin_at` and `:end_at` options as `find_each`. +The `find_in_batches` method accepts the same `:batch_size`, `:start` and `:finish` options as `find_each`. Conditions ---------- @@ -740,7 +766,7 @@ SELECT "articles".* FROM "articles" WHERE (id > 10) ORDER BY id desc LIMIT 20 The `reorder` method overrides the default scope order. For example: ```ruby -class Article < ActiveRecord::Base +class Article < ApplicationRecord has_many :comments, -> { order('posted_at DESC') } end @@ -889,7 +915,7 @@ This behavior can be turned off by setting `ActiveRecord::Base.lock_optimistical To override the name of the `lock_version` column, `ActiveRecord::Base` provides a class attribute called `locking_column`: ```ruby -class Client < ActiveRecord::Base +class Client < ApplicationRecord self.locking_column = :lock_client_column end ``` @@ -970,26 +996,26 @@ Active Record lets you use the names of the [associations](association_basics.ht For example, consider the following `Category`, `Article`, `Comment`, `Guest` and `Tag` models: ```ruby -class Category < ActiveRecord::Base +class Category < ApplicationRecord has_many :articles end -class Article < ActiveRecord::Base +class Article < ApplicationRecord belongs_to :category has_many :comments has_many :tags end -class Comment < ActiveRecord::Base +class Comment < ApplicationRecord belongs_to :article has_one :guest end -class Guest < ActiveRecord::Base +class Guest < ApplicationRecord belongs_to :comment end -class Tag < ActiveRecord::Base +class Tag < ApplicationRecord belongs_to :article end ``` @@ -1059,6 +1085,8 @@ SELECT categories.* FROM categories INNER JOIN tags ON tags.article_id = articles.id ``` +Or, in English: "return all categories that have articles, where those articles have a comment made by a guest, and where those articles also have a tag." + #### Specifying Conditions on the Joined Tables You can specify conditions on the joined tables using the regular [Array](#array-conditions) and [String](#pure-string-conditions) conditions. [Hash conditions](#hash-conditions) provide a special syntax for specifying conditions for the joined tables: @@ -1199,7 +1227,7 @@ Scoping allows you to specify commonly-used queries which can be referenced as m To define a simple scope, we use the `scope` method inside the class, passing the query that we'd like to run when this scope is called: ```ruby -class Article < ActiveRecord::Base +class Article < ApplicationRecord scope :published, -> { where(published: true) } end ``` @@ -1207,7 +1235,7 @@ end This is exactly the same as defining a class method, and which you use is a matter of personal preference: ```ruby -class Article < ActiveRecord::Base +class Article < ApplicationRecord def self.published where(published: true) end @@ -1217,7 +1245,7 @@ end Scopes are also chainable within scopes: ```ruby -class Article < ActiveRecord::Base +class Article < ApplicationRecord scope :published, -> { where(published: true) } scope :published_and_commented, -> { published.where("comments_count > 0") } end @@ -1241,7 +1269,7 @@ category.articles.published # => [published articles belonging to this category] Your scope can take arguments: ```ruby -class Article < ActiveRecord::Base +class Article < ApplicationRecord scope :created_before, ->(time) { where("created_at < ?", time) } end ``` @@ -1255,7 +1283,7 @@ Article.created_before(Time.zone.now) However, this is just duplicating the functionality that would be provided to you by a class method. ```ruby -class Article < ActiveRecord::Base +class Article < ApplicationRecord def self.created_before(time) where("created_at < ?", time) end @@ -1268,13 +1296,35 @@ Using a class method is the preferred way to accept arguments for scopes. These category.articles.created_before(time) ``` +### Using conditionals + +Your scope can utilize conditionals: + +```ruby +class Article < ApplicationRecord + scope :created_before, ->(time) { where("created_at < ?", time) if time.present? } +end +``` + +Like the other examples, this will behave similarly to a class method. + +```ruby +class Article < ApplicationRecord + def self.created_before(time) + where("created_at < ?", time) if time.present? + end +end +``` + +However, there is one important caveat: A scope will always return an `ActiveRecord::Relation` object, even if the conditional evaluates to `false`, whereas a class method, will return `nil`. This can cause `NoMethodError` when chaining class methods with conditionals, if any of the conditionals return `false`. + ### Applying a default scope If we wish for a scope to be applied across all queries to the model we can use the `default_scope` method within the model itself. ```ruby -class Client < ActiveRecord::Base +class Client < ApplicationRecord default_scope { where("removed_at IS NULL") } end ``` @@ -1290,7 +1340,7 @@ If you need to do more complex things with a default scope, you can alternativel define it as a class method: ```ruby -class Client < ActiveRecord::Base +class Client < ApplicationRecord def self.default_scope # Should return an ActiveRecord::Relation. end @@ -1301,7 +1351,7 @@ NOTE: The `default_scope` is also applied while creating/building a record. It is not applied while updating a record. E.g.: ```ruby -class Client < ActiveRecord::Base +class Client < ApplicationRecord default_scope { where(active: true) } end @@ -1314,7 +1364,7 @@ Client.unscoped.new # => #<Client id: nil, active: nil> Just like `where` clauses scopes are merged using `AND` conditions. ```ruby -class User < ActiveRecord::Base +class User < ApplicationRecord scope :active, -> { where state: 'active' } scope :inactive, -> { where state: 'inactive' } end @@ -1343,7 +1393,7 @@ One important caveat is that `default_scope` will be prepended in `scope` and `where` conditions. ```ruby -class User < ActiveRecord::Base +class User < ApplicationRecord default_scope { where state: 'pending' } scope :active, -> { where state: 'active' } scope :inactive, -> { where state: 'inactive' } @@ -1374,8 +1424,15 @@ Client.unscoped.load This method removes all scoping and will do a normal query on the table. -Note that chaining `unscoped` with a `scope` does not work. In these cases, it is -recommended that you use the block form of `unscoped`: +```ruby +Client.unscoped.all +# SELECT "clients".* FROM "clients" + +Client.where(published: false).unscoped.all +# SELECT "clients".* FROM "clients" +``` + +`unscoped` can also accept a block. ```ruby Client.unscoped { @@ -1392,6 +1449,36 @@ You can specify an exclamation point (`!`) on the end of the dynamic finders to If you want to find both by name and locked, you can chain these finders together by simply typing "`and`" between the fields. For example, `Client.find_by_first_name_and_locked("Ryan", true)`. +Enums +----- + +The `enum` macro maps an integer column to a set of possible values. + +```ruby +class Book < ApplicationRecord + enum availability: [:available, :unavailable] +end +``` + +This will automatically create the corresponding [scopes](#scopes) to query the +model. Methods to transition between states and query the current state are also +added. + +```ruby +# Both examples below query just available books. +Book.available +# or +Book.where(availability: :available) + +book = Book.new(availability: :available) +book.available? # => true +book.unavailable! # => true +book.available? # => false +``` + +Read the full documentation about enums +[in the Rails API docs](http://api.rubyonrails.org/classes/ActiveRecord/Enum.html). + Understanding The Method Chaining --------------------------------- @@ -1620,7 +1707,7 @@ a large or often-running query. However, any model method overrides will not be available. For example: ```ruby -class Client < ActiveRecord::Base +class Client < ApplicationRecord def name "I am #{super}" end @@ -1655,7 +1742,7 @@ Person.ids ``` ```ruby -class Person < ActiveRecord::Base +class Person < ApplicationRecord self.primary_key = "person_id" end |