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diff --git a/guides/source/active_record_querying.md b/guides/source/active_record_querying.md index 8ea0f383c0..63658e7c8b 100644 --- a/guides/source/active_record_querying.md +++ b/guides/source/active_record_querying.md @@ -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` @@ -69,6 +69,7 @@ The methods are: * `having` * `includes` * `joins` +* `left_outer_joins` * `limit` * `lock` * `none` @@ -80,7 +81,7 @@ The methods are: * `reorder` * `reverse_order` * `select` -* `uniq` +* `distinct` * `where` All of the above methods return an instance of `ActiveRecord::Relation`. @@ -169,7 +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 @@ -184,6 +185,8 @@ SELECT * FROM clients ORDER BY clients.id ASC LIMIT 1 The `first` method returns `nil` if no matching record is found and no exception will be raised. +If your [default scope](active_record_querying.html#applying-a-default-scope) contains an order method, `first` will return the first record according to this ordering. + You can pass in a numerical argument to the `first` method to return up to that number of results. For example ```ruby @@ -201,11 +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 @@ -220,6 +236,8 @@ SELECT * FROM clients ORDER BY clients.id DESC LIMIT 1 The `last` method returns `nil` if no matching record is found and no exception will be raised. +If your [default scope](active_record_querying.html#applying-a-default-scope) contains an order method, `last` will return the last record according to this ordering. + You can pass in a numerical argument to the `last` method to return up to that number of results. For example ```ruby @@ -237,6 +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` @@ -317,7 +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`** @@ -329,34 +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` @@ -371,7 +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 ---------- @@ -735,7 +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 @@ -884,7 +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 ``` @@ -935,58 +966,63 @@ end Joining Tables -------------- -Active Record provides a finder method called `joins` for specifying `JOIN` clauses on the resulting SQL. There are multiple ways to use the `joins` method. +Active Record provides two finder methods for specifying `JOIN` clauses on the +resulting SQL: `joins` and `left_outer_joins`. +While `joins` should be used for `INNER JOIN` or custom queries, +`left_outer_joins` is used for queries using `LEFT OUTER JOIN`. -### Using a String SQL Fragment +### `joins` + +There are multiple ways to use the `joins` method. + +#### Using a String SQL Fragment You can just supply the raw SQL specifying the `JOIN` clause to `joins`: ```ruby -Client.joins('LEFT OUTER JOIN addresses ON addresses.client_id = clients.id') +Author.joins("INNER JOIN posts ON posts.author_id = author.id AND posts.published = 't'") ``` This will result in the following SQL: ```sql -SELECT clients.* FROM clients LEFT OUTER JOIN addresses ON addresses.client_id = clients.id +SELECT clients.* FROM clients INNER JOIN posts ON posts.author_id = author.id AND posts.published = 't' ``` -### Using Array/Hash of Named Associations - -WARNING: This method only works with `INNER JOIN`. +#### Using Array/Hash of Named Associations Active Record lets you use the names of the [associations](association_basics.html) defined on the model as a shortcut for specifying `JOIN` clauses for those associations when using the `joins` method. 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 ``` Now all of the following will produce the expected join queries using `INNER JOIN`: -#### Joining a Single Association +##### Joining a Single Association ```ruby Category.joins(:articles) @@ -999,7 +1035,7 @@ SELECT categories.* FROM categories INNER JOIN articles ON articles.category_id = categories.id ``` -Or, in English: "return a Category object for all categories with articles". Note that you will see duplicate categories if more than one article has the same category. If you want unique categories, you can use `Category.joins(:articles).uniq`. +Or, in English: "return a Category object for all categories with articles". Note that you will see duplicate categories if more than one article has the same category. If you want unique categories, you can use `Category.joins(:articles).distinct`. #### Joining Multiple Associations @@ -1017,7 +1053,7 @@ SELECT articles.* FROM articles Or, in English: "return all articles that have a category and at least one comment". Note again that articles with multiple comments will show up multiple times. -#### Joining Nested Associations (Single Level) +##### Joining Nested Associations (Single Level) ```ruby Article.joins(comments: :guest) @@ -1033,7 +1069,7 @@ SELECT articles.* FROM articles Or, in English: "return all articles that have a comment made by a guest." -#### Joining Nested Associations (Multiple Level) +##### Joining Nested Associations (Multiple Level) ```ruby Category.joins(articles: [{ comments: :guest }, :tags]) @@ -1049,7 +1085,9 @@ SELECT categories.* FROM categories INNER JOIN tags ON tags.article_id = articles.id ``` -### Specifying Conditions on the Joined Tables +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: @@ -1067,6 +1105,26 @@ Client.joins(:orders).where(orders: { created_at: time_range }) This will find all clients who have orders that were created yesterday, again using a `BETWEEN` SQL expression. +### `left_outer_joins` + +If you want to select a set of records whether or not they have associated +records you can use the `left_outer_joins` method. + +```ruby +Author.left_outer_joins(:posts).uniq.select('authors.*, COUNT(posts.*) AS posts_count').group('authors.id') +``` + +Which produces: + +```sql +SELECT DISTINCT authors.*, COUNT(posts.*) AS posts_count FROM "authors" +LEFT OUTER JOIN posts ON posts.author_id = authors.id GROUP BY authors.id +``` + +Which means: "return all authors with their count of posts, whether or not they +have any posts at all" + + Eager Loading Associations -------------------------- @@ -1169,7 +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 ``` @@ -1177,7 +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 @@ -1187,7 +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 @@ -1211,7 +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 ``` @@ -1225,7 +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 @@ -1244,7 +1302,7 @@ If we wish for a scope to be applied across all queries to the model we can use `default_scope` method within the model itself. ```ruby -class Client < ActiveRecord::Base +class Client < ApplicationRecord default_scope { where("removed_at IS NULL") } end ``` @@ -1260,7 +1318,7 @@ 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 @@ -1271,7 +1329,7 @@ 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 @@ -1284,7 +1342,7 @@ 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 @@ -1313,7 +1371,7 @@ 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' } @@ -1344,8 +1402,15 @@ 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 { @@ -1362,6 +1427,36 @@ 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 --------------------------------- @@ -1590,7 +1685,7 @@ 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 @@ -1625,7 +1720,7 @@ Person.ids ``` ```ruby -class Person < ActiveRecord::Base +class Person < ApplicationRecord self.primary_key = "person_id" end |