Module: ActiveRecord::QueryMethods

Extended by:
ActiveSupport::Concern
Includes:
ActiveModel::ForbiddenAttributesProtection
Included in:
Relation
Defined in:
activerecord/lib/active_record/relation/query_methods.rb

Defined Under Namespace

Classes: WhereChain

Constant Summary collapse

FROZEN_EMPTY_ARRAY =
[].freeze
FROZEN_EMPTY_HASH =
{}.freeze
VALID_UNSCOPING_VALUES =
Set.new([:where, :select, :group, :order, :lock,
:limit, :offset, :joins, :left_outer_joins, :annotate,
:includes, :from, :readonly, :having, :optimizer_hints])

Instance Method Summary collapse

Methods included from ActiveSupport::Concern

append_features, class_methods, extended, included, prepend_features, prepended

Instance Method Details

#_select!(*fields) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 310

def _select!(*fields) # :nodoc:
  fields.compact_blank!
  fields.flatten!
  self.select_values += fields
  self
end

#annotate(*args) ⇒ Object

Adds an SQL comment to queries generated from this relation. For example:

User.annotate("selecting user names").select(:name)
# SELECT "users"."name" FROM "users" /* selecting user names */

User.annotate("selecting", "user", "names").select(:name)
# SELECT "users"."name" FROM "users" /* selecting */ /* user */ /* names */

The SQL block comment delimiters, “/*” and “*/”, will be added automatically.


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1050

def annotate(*args)
  check_if_method_has_arguments!(:annotate, args)
  spawn.annotate!(*args)
end

#annotate!(*args) ⇒ Object

Like #annotate, but modifies relation in place.


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1056

def annotate!(*args) # :nodoc:
  self.annotate_values += args
  self
end

#arel(aliases = nil) ⇒ Object

Returns the Arel object associated with the relation.


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1062

def arel(aliases = nil) # :nodoc:
  @arel ||= build_arel(aliases)
end

#construct_join_dependency(associations, join_type) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1066

def construct_join_dependency(associations, join_type) # :nodoc:
  ActiveRecord::Associations::JoinDependency.new(
    klass, table, associations, join_type
  )
end

#create_with(value) ⇒ Object

Sets attributes to be used when creating new records from a relation object.

users = User.where(name: 'Oscar')
users.new.name # => 'Oscar'

users = users.create_with(name: 'DHH')
users.new.name # => 'DHH'

You can pass nil to #create_with to reset attributes:

users = users.create_with(nil)
users.new.name # => 'Oscar'

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 883

def create_with(value)
  spawn.create_with!(value)
end

#create_with!(value) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 887

def create_with!(value) # :nodoc:
  if value
    value = sanitize_forbidden_attributes(value)
    self.create_with_value = create_with_value.merge(value)
  else
    self.create_with_value = FROZEN_EMPTY_HASH
  end

  self
end

#distinct(value = true) ⇒ Object

Specifies whether the records should be unique or not. For example:

User.select(:name)
# Might return two records with the same name

User.select(:name).distinct
# Returns 1 record per distinct name

User.select(:name).distinct.distinct(false)
# You can also remove the uniqueness

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 930

def distinct(value = true)
  spawn.distinct!(value)
end

#distinct!(value = true) ⇒ Object

Like #distinct, but modifies relation in place.


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 935

def distinct!(value = true) # :nodoc:
  self.distinct_value = value
  self
end

#eager_load(*args) ⇒ Object

Forces eager loading by performing a LEFT OUTER JOIN on args:

User.eager_load(:posts)
# SELECT "users"."id" AS t0_r0, "users"."name" AS t0_r1, ...
# FROM "users" LEFT OUTER JOIN "posts" ON "posts"."user_id" =
# "users"."id"

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 197

def eager_load(*args)
  check_if_method_has_arguments!(:eager_load, args)
  spawn.eager_load!(*args)
end

#eager_load!(*args) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 202

def eager_load!(*args) # :nodoc:
  self.eager_load_values |= args
  self
end

#extending(*modules, &block) ⇒ Object

Used to extend a scope with additional methods, either through a module or through a block provided.

The object returned is a relation, which can be further extended.

Using a module

module Pagination
  def page(number)
    # pagination code goes here
  end
end

scope = Model.all.extending(Pagination)
scope.page(params[:page])

You can also pass a list of modules:

scope = Model.all.extending(Pagination, SomethingElse)

Using a block

scope = Model.all.extending do
  def page(number)
    # pagination code goes here
  end
end
scope.page(params[:page])

You can also use a block and a module list:

scope = Model.all.extending(Pagination) do
  def per_page(number)
    # pagination code goes here
  end
end

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 976

def extending(*modules, &block)
  if modules.any? || block
    spawn.extending!(*modules, &block)
  else
    self
  end
end

#extending!(*modules, &block) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 984

def extending!(*modules, &block) # :nodoc:
  modules << Module.new(&block) if block
  modules.flatten!

  self.extending_values += modules
  extend(*extending_values) if extending_values.any?

  self
end

#extract_associated(association) ⇒ Object

Extracts a named association from the relation. The named association is first preloaded, then the individual association records are collected from the relation. Like so:

.memberships.extract_associated(:user)
# => Returns collection of User records

This is short-hand for:

.memberships.preload(:user).collect(&:user)

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 230

def extract_associated(association)
  preload(association).collect(&association)
end

#from(value, subquery_name = nil) ⇒ Object

Specifies table from which the records will be fetched. For example:

Topic.select('title').from('posts')
# SELECT title FROM posts

Can accept other relation objects. For example:

Topic.select('title').from(Topic.approved)
# SELECT title FROM (SELECT * FROM topics WHERE approved = 't') subquery

Topic.select('a.title').from(Topic.approved, :a)
# SELECT a.title FROM (SELECT * FROM topics WHERE approved = 't') a

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 911

def from(value, subquery_name = nil)
  spawn.from!(value, subquery_name)
end

#from!(value, subquery_name = nil) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 915

def from!(value, subquery_name = nil) # :nodoc:
  self.from_clause = Relation::FromClause.new(value, subquery_name)
  self
end

#group(*args) ⇒ Object

Allows to specify a group attribute:

User.group(:name)
# SELECT "users".* FROM "users" GROUP BY name

Returns an array with distinct records based on the group attribute:

User.select([:id, :name])
# => [#<User id: 1, name: "Oscar">, #<User id: 2, name: "Oscar">, #<User id: 3, name: "Foo">]

User.group(:name)
# => [#<User id: 3, name: "Foo", ...>, #<User id: 2, name: "Oscar", ...>]

User.group('name AS grouped_name, age')
# => [#<User id: 3, name: "Foo", age: 21, ...>, #<User id: 2, name: "Oscar", age: 21, ...>, #<User id: 5, name: "Foo", age: 23, ...>]

Passing in an array of attributes to group by is also supported.

User.select([:id, :first_name]).group(:id, :first_name).first(3)
# => [#<User id: 1, first_name: "Bill">, #<User id: 2, first_name: "Earl">, #<User id: 3, first_name: "Beto">]

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 358

def group(*args)
  check_if_method_has_arguments!(:group, args)
  spawn.group!(*args)
end

#group!(*args) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 363

def group!(*args) # :nodoc:
  args.flatten!

  self.group_values |= args
  self
end

#having(opts, *rest) ⇒ Object

Allows to specify a HAVING clause. Note that you can't use HAVING without also specifying a GROUP clause.

Order.having('SUM(price) > 30').group('user_id')

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 745

def having(opts, *rest)
  opts.blank? ? self : spawn.having!(opts, *rest)
end

#having!(opts, *rest) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 749

def having!(opts, *rest) # :nodoc:
  opts = sanitize_forbidden_attributes(opts)
  references!(PredicateBuilder.references(opts)) if Hash === opts

  self.having_clause += having_clause_factory.build(opts, rest)
  self
end

#includes(*args) ⇒ Object

Specify relationships to be included in the result set. For example:

users = User.includes(:address)
users.each do |user|
  user.address.city
end

allows you to access the address attribute of the User model without firing an additional query. This will often result in a performance improvement over a simple join.

You can also specify multiple relationships, like this:

users = User.includes(:address, :friends)

Loading nested relationships is possible using a Hash:

users = User.includes(:address, friends: [:address, :followers])

conditions

If you want to add string conditions to your included models, you'll have to explicitly reference them. For example:

User.includes(:posts).where('posts.name = ?', 'example')

Will throw an error, but this will work:

User.includes(:posts).where('posts.name = ?', 'example').references(:posts)

Note that #includes works with association names while #references needs the actual table name.

If you pass the conditions via hash, you don't need to call #references explicitly, as #where references the tables for you. For example, this will work correctly:

User.includes(:posts).where(posts: { name: 'example' })

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 178

def includes(*args)
  check_if_method_has_arguments!(:includes, args)
  spawn.includes!(*args)
end

#includes!(*args) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 183

def includes!(*args) # :nodoc:
  args.compact_blank!
  args.flatten!

  self.includes_values |= args
  self
end

#joins(*args) ⇒ Object

Performs a joins on args. The given symbol(s) should match the name of the association(s).

User.joins(:posts)
# SELECT "users".*
# FROM "users"
# INNER JOIN "posts" ON "posts"."user_id" = "users"."id"

Multiple joins:

User.joins(:posts, :account)
# SELECT "users".*
# FROM "users"
# INNER JOIN "posts" ON "posts"."user_id" = "users"."id"
# INNER JOIN "accounts" ON "accounts"."id" = "users"."account_id"

Nested joins:

User.joins(posts: [:comments])
# SELECT "users".*
# FROM "users"
# INNER JOIN "posts" ON "posts"."user_id" = "users"."id"
# INNER JOIN "comments" "comments_posts"
#   ON "comments_posts"."post_id" = "posts"."id"

You can use strings in order to customize your joins:

User.joins("LEFT JOIN bookmarks ON bookmarks.bookmarkable_type = 'Post' AND bookmarks.user_id = users.id")
# SELECT "users".* FROM "users" LEFT JOIN bookmarks ON bookmarks.bookmarkable_type = 'Post' AND bookmarks.user_id = users.id

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 526

def joins(*args)
  check_if_method_has_arguments!(:joins, args)
  spawn.joins!(*args)
end

#joins!(*args) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 531

def joins!(*args) # :nodoc:
  args.compact!
  args.flatten!
  self.joins_values |= args
  self
end

#left_outer_joins(*args) ⇒ Object Also known as: left_joins

Performs a left outer joins on args:

User.left_outer_joins(:posts)
=> SELECT "users".* FROM "users" LEFT OUTER JOIN "posts" ON "posts"."user_id" = "users"."id"

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 543

def left_outer_joins(*args)
  check_if_method_has_arguments!(__callee__, args)
  spawn.left_outer_joins!(*args)
end

#left_outer_joins!(*args) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 549

def left_outer_joins!(*args) # :nodoc:
  args.compact!
  args.flatten!
  self.left_outer_joins_values |= args
  self
end

#limit(value) ⇒ Object

Specifies a limit for the number of records to retrieve.

User.limit(10) # generated SQL has 'LIMIT 10'

User.limit(10).limit(20) # generated SQL has 'LIMIT 20'

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 762

def limit(value)
  spawn.limit!(value)
end

#limit!(value) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 766

def limit!(value) # :nodoc:
  self.limit_value = value
  self
end

#lock(locks = true) ⇒ Object

Specifies locking settings (default to true). For more information on locking, please see ActiveRecord::Locking.


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 789

def lock(locks = true)
  spawn.lock!(locks)
end

#lock!(locks = true) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 793

def lock!(locks = true) # :nodoc:
  case locks
  when String, TrueClass, NilClass
    self.lock_value = locks || true
  else
    self.lock_value = false
  end

  self
end

#noneObject

Returns a chainable relation with zero records.

The returned relation implements the Null Object pattern. It is an object with defined null behavior and always returns an empty array of records without querying the database.

Any subsequent condition chained to the returned relation will continue generating an empty relation and will not fire any query to the database.

Used in cases where a method or scope could return zero records but the result needs to be chainable.

For example:

@posts = current_user.visible_posts.where(name: params[:name])
# the visible_posts method is expected to return a chainable Relation

def visible_posts
  case role
  when 'Country Manager'
    Post.where(country: country)
  when 'Reviewer'
    Post.published
  when 'Bad User'
    Post.none # It can't be chained if [] is returned.
  end
end

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 832

def none
  spawn.none!
end

#none!Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 836

def none! # :nodoc:
  where!("1=0").extending!(NullRelation)
end

#offset(value) ⇒ Object

Specifies the number of rows to skip before returning rows.

User.offset(10) # generated SQL has "OFFSET 10"

Should be used with order.

User.offset(10).order("name ASC")

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 778

def offset(value)
  spawn.offset!(value)
end

#offset!(value) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 782

def offset!(value) # :nodoc:
  self.offset_value = value
  self
end

#optimizer_hints(*args) ⇒ Object

Specify optimizer hints to be used in the SELECT statement.

Example (for MySQL):

Topic.optimizer_hints("MAX_EXECUTION_TIME(50000)", "NO_INDEX_MERGE(topics)")
# SELECT /*+ MAX_EXECUTION_TIME(50000) NO_INDEX_MERGE(topics) */ `topics`.* FROM `topics`

Example (for PostgreSQL with pg_hint_plan):

Topic.optimizer_hints("SeqScan(topics)", "Parallel(topics 8)")
# SELECT /*+ SeqScan(topics) Parallel(topics 8) */ "topics".* FROM "topics"

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1005

def optimizer_hints(*args)
  check_if_method_has_arguments!(:optimizer_hints, args)
  spawn.optimizer_hints!(*args)
end

#optimizer_hints!(*args) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1010

def optimizer_hints!(*args) # :nodoc:
  args.flatten!

  self.optimizer_hints_values |= args
  self
end

#or(other) ⇒ Object

Returns a new relation, which is the logical union of this relation and the one passed as an argument.

The two relations must be structurally compatible: they must be scoping the same model, and they must differ only by #where (if no #group has been defined) or #having (if a #group is present). Neither relation may have a #limit, #offset, or #distinct set.

Post.where("id = 1").or(Post.where("author_id = 3"))
# SELECT `posts`.* FROM `posts` WHERE ((id = 1) OR (author_id = 3))

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 719

def or(other)
  unless other.is_a? Relation
    raise ArgumentError, "You have passed #{other.class.name} object to #or. Pass an ActiveRecord::Relation object instead."
  end

  spawn.or!(other)
end

#or!(other) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 727

def or!(other) # :nodoc:
  incompatible_values = structurally_incompatible_values_for_or(other)

  unless incompatible_values.empty?
    raise ArgumentError, "Relation passed to #or must be structurally compatible. Incompatible values: #{incompatible_values}"
  end

  self.where_clause = self.where_clause.or(other.where_clause)
  self.having_clause = having_clause.or(other.having_clause)
  self.references_values += other.references_values

  self
end

#order(*args) ⇒ Object

Allows to specify an order attribute:

User.order(:name)
# SELECT "users".* FROM "users" ORDER BY "users"."name" ASC

User.order(email: :desc)
# SELECT "users".* FROM "users" ORDER BY "users"."email" DESC

User.order(:name, email: :desc)
# SELECT "users".* FROM "users" ORDER BY "users"."name" ASC, "users"."email" DESC

User.order('name')
# SELECT "users".* FROM "users" ORDER BY name

User.order('name DESC')
# SELECT "users".* FROM "users" ORDER BY name DESC

User.order('name DESC, email')
# SELECT "users".* FROM "users" ORDER BY name DESC, email

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 389

def order(*args)
  check_if_method_has_arguments!(:order, args)
  spawn.order!(*args)
end

#order!(*args) ⇒ Object

Same as #order but operates on relation in-place instead of copying.


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 395

def order!(*args) # :nodoc:
  preprocess_order_args(args)

  self.order_values += args
  self
end

#preload(*args) ⇒ Object

Allows preloading of args, in the same way that #includes does:

User.preload(:posts)
# SELECT "posts".* FROM "posts" WHERE "posts"."user_id" IN (1, 2, 3)

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 211

def preload(*args)
  check_if_method_has_arguments!(:preload, args)
  spawn.preload!(*args)
end

#preload!(*args) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 216

def preload!(*args) # :nodoc:
  self.preload_values |= args
  self
end

#readonly(value = true) ⇒ Object

Sets readonly attributes for the returned relation. If value is true (default), attempting to update a record will result in an error.

users = User.readonly
users.first.save
=> ActiveRecord::ReadOnlyRecord: User is marked as readonly

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 846

def readonly(value = true)
  spawn.readonly!(value)
end

#readonly!(value = true) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 850

def readonly!(value = true) # :nodoc:
  self.readonly_value = value
  self
end

#references(*table_names) ⇒ Object

Use to indicate that the given table_names are referenced by an SQL string, and should therefore be JOINed in any query rather than loaded separately. This method only works in conjunction with #includes. See #includes for more details.

User.includes(:posts).where("posts.name = 'foo'")
# Doesn't JOIN the posts table, resulting in an error.

User.includes(:posts).where("posts.name = 'foo'").references(:posts)
# Query now knows the string references posts, so adds a JOIN

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 244

def references(*table_names)
  check_if_method_has_arguments!(:references, table_names)
  spawn.references!(*table_names)
end

#references!(*table_names) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 249

def references!(*table_names) # :nodoc:
  table_names.flatten!
  table_names.map!(&:to_s)

  self.references_values |= table_names
  self
end

#reorder(*args) ⇒ Object

Replaces any existing order defined on the relation with the specified order.

User.order('email DESC').reorder('id ASC') # generated SQL has 'ORDER BY id ASC'

Subsequent calls to order on the same relation will be appended. For example:

User.order('email DESC').reorder('id ASC').order('name ASC')

generates a query with 'ORDER BY id ASC, name ASC'.


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 411

def reorder(*args)
  check_if_method_has_arguments!(:reorder, args)
  spawn.reorder!(*args)
end

#reorder!(*args) ⇒ Object

Same as #reorder but operates on relation in-place instead of copying.


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 417

def reorder!(*args) # :nodoc:
  preprocess_order_args(args) unless args.all?(&:blank?)

  self.reordering_value = true
  self.order_values = args
  self
end

#reselect(*args) ⇒ Object

Allows you to change a previously set select statement.

Post.select(:title, :body)
# SELECT `posts`.`title`, `posts`.`body` FROM `posts`

Post.select(:title, :body).reselect(:created_at)
# SELECT `posts`.`created_at` FROM `posts`

This is short-hand for unscope(:select).select(fields). Note that we're unscoping the entire select statement.


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 327

def reselect(*args)
  check_if_method_has_arguments!(:reselect, args)
  spawn.reselect!(*args)
end

#reselect!(*args) ⇒ Object

Same as #reselect but operates on relation in-place instead of copying.


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 333

def reselect!(*args) # :nodoc:
  self.select_values = args
  self
end

#reverse_orderObject

Reverse the existing order clause on the relation.

User.order('name ASC').reverse_order # generated SQL has 'ORDER BY name DESC'

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1020

def reverse_order
  spawn.reverse_order!
end

#reverse_order!Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1024

def reverse_order! # :nodoc:
  orders = order_values.uniq
  orders.compact_blank!
  self.order_values = reverse_sql_order(orders)
  self
end

#rewhere(conditions) ⇒ Object

Allows you to change a previously set where condition for a given attribute, instead of appending to that condition.

Post.where(trashed: true).where(trashed: false)
# WHERE `trashed` = 1 AND `trashed` = 0

Post.where(trashed: true).rewhere(trashed: false)
# WHERE `trashed` = 0

Post.where(active: true).where(trashed: true).rewhere(trashed: false)
# WHERE `active` = 1 AND `trashed` = 0

This is short-hand for unscope(where: conditions.keys).where(conditions). Note that unlike reorder, we're only unscoping the named conditions – not the entire where statement.


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 705

def rewhere(conditions)
  unscope(where: conditions.keys).where(conditions)
end

#select(*fields) ⇒ Object

Works in two unique ways.

First: takes a block so it can be used just like Array#select.

Model.all.select { |m| m.field == value }

This will build an array of objects from the database for the scope, converting them into an array and iterating through them using Array#select.

Second: Modifies the SELECT statement for the query so that only certain fields are retrieved:

Model.select(:field)
# => [#<Model id: nil, field: "value">]

Although in the above example it looks as though this method returns an array, it actually returns a relation object and can have other query methods appended to it, such as the other methods in ActiveRecord::QueryMethods.

The argument to the method can also be an array of fields.

Model.select(:field, :other_field, :and_one_more)
# => [#<Model id: nil, field: "value", other_field: "value", and_one_more: "value">]

You can also use one or more strings, which will be used unchanged as SELECT fields.

Model.select('field AS field_one', 'other_field AS field_two')
# => [#<Model id: nil, field: "value", other_field: "value">]

If an alias was specified, it will be accessible from the resulting objects:

Model.select('field AS field_one').first.field_one
# => "value"

Accessing attributes of an object that do not have fields retrieved by a select except id will throw ActiveModel::MissingAttributeError:

Model.select(:field).first.other_field
# => ActiveModel::MissingAttributeError: missing attribute: other_field

Raises:

  • (ArgumentError)

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 297

def select(*fields)
  if block_given?
    if fields.any?
      raise ArgumentError, "`select' with block doesn't take arguments."
    end

    return super()
  end

  raise ArgumentError, "Call `select' with at least one field" if fields.empty?
  spawn._select!(*fields)
end

#skip_preloading!Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1036

def skip_preloading! # :nodoc:
  self.skip_preloading_value = true
  self
end

#skip_query_cache!(value = true) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1031

def skip_query_cache!(value = true) # :nodoc:
  self.skip_query_cache_value = value
  self
end

#strict_loading(value = true) ⇒ Object

Sets the returned relation to strict_loading mode. This will raise an error if the record tries to lazily load an association.

user = User.strict_loading.first
user.comments.to_a
=> ActiveRecord::StrictLoadingViolationError

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 861

def strict_loading(value = true)
  spawn.strict_loading!(value)
end

#strict_loading!(value = true) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 865

def strict_loading!(value = true) # :nodoc:
  self.strict_loading_value = value
  self
end

#unscope(*args) ⇒ Object

Removes an unwanted relation that is already defined on a chain of relations. This is useful when passing around chains of relations and would like to modify the relations without reconstructing the entire chain.

User.order('email DESC').unscope(:order) == User.all

The method arguments are symbols which correspond to the names of the methods which should be unscoped. The valid arguments are given in VALID_UNSCOPING_VALUES. The method can also be called with multiple arguments. For example:

User.order('email DESC').select('id').where(name: "John")
    .unscope(:order, :select, :where) == User.all

One can additionally pass a hash as an argument to unscope specific :where values. This is done by passing a hash with a single key-value pair. The key should be :where and the value should be the where value to unscope. For example:

User.where(name: "John", active: true).unscope(where: :name)
    == User.where(active: true)

This method is similar to #except, but unlike #except, it persists across merges:

User.order('email').merge(User.except(:order))
    == User.order('email')

User.order('email').merge(User.unscope(:order))
    == User.all

This means it can be used in association definitions:

has_many :comments, -> { unscope(where: :trashed) }

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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 462

def unscope(*args)
  check_if_method_has_arguments!(:unscope, args)
  spawn.unscope!(*args)
end

#unscope!(*args) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 467

def unscope!(*args) # :nodoc:
  args.flatten!
  self.unscope_values += args

  args.each do |scope|
    case scope
    when Symbol
      scope = :left_outer_joins if scope == :left_joins
      if !VALID_UNSCOPING_VALUES.include?(scope)
        raise ArgumentError, "Called unscope() with invalid unscoping argument ':#{scope}'. Valid arguments are :#{VALID_UNSCOPING_VALUES.to_a.join(", :")}."
      end
      assert_mutability!
      @values.delete(scope)
    when Hash
      scope.each do |key, target_value|
        if key != :where
          raise ArgumentError, "Hash arguments in .unscope(*args) must have :where as the key."
        end

        target_values = Array(target_value).map(&:to_s)
        self.where_clause = where_clause.except(*target_values)
      end
    else
      raise ArgumentError, "Unrecognized scoping: #{args.inspect}. Use .unscope(where: :attribute_name) or .unscope(:order), for example."
    end
  end

  self
end

#where(opts = :chain, *rest) ⇒ Object

Returns a new relation, which is the result of filtering the current relation according to the conditions in the arguments.

#where accepts conditions in one of several formats. In the examples below, the resulting SQL is given as an illustration; the actual query generated may be different depending on the database adapter.

string

A single string, without additional arguments, is passed to the query constructor as an SQL fragment, and used in the where clause of the query.

Client.where("orders_count = '2'")
# SELECT * from clients where orders_count = '2';

Note that building your own string from user input may expose your application to injection attacks if not done properly. As an alternative, it is recommended to use one of the following methods.

array

If an array is passed, then the first element of the array is treated as a template, and the remaining elements are inserted into the template to generate the condition. Active Record takes care of building the query to avoid injection attacks, and will convert from the ruby type to the database type where needed. Elements are inserted into the string in the order in which they appear.

User.where(["name = ? and email = ?", "Joe", "[email protected]"])
# SELECT * FROM users WHERE name = 'Joe' AND email = '[email protected]';

Alternatively, you can use named placeholders in the template, and pass a hash as the second element of the array. The names in the template are replaced with the corresponding values from the hash.

User.where(["name = :name and email = :email", { name: "Joe", email: "[email protected]" }])
# SELECT * FROM users WHERE name = 'Joe' AND email = '[email protected]';

This can make for more readable code in complex queries.

Lastly, you can use sprintf-style % escapes in the template. This works slightly differently than the previous methods; you are responsible for ensuring that the values in the template are properly quoted. The values are passed to the connector for quoting, but the caller is responsible for ensuring they are enclosed in quotes in the resulting SQL. After quoting, the values are inserted using the same escapes as the Ruby core method Kernel::sprintf.

User.where(["name = '%s' and email = '%s'", "Joe", "[email protected]"])
# SELECT * FROM users WHERE name = 'Joe' AND email = '[email protected]';

If #where is called with multiple arguments, these are treated as if they were passed as the elements of a single array.

User.where("name = :name and email = :email", { name: "Joe", email: "[email protected]" })
# SELECT * FROM users WHERE name = 'Joe' AND email = '[email protected]';

When using strings to specify conditions, you can use any operator available from the database. While this provides the most flexibility, you can also unintentionally introduce dependencies on the underlying database. If your code is intended for general consumption, test with multiple database backends.

hash

#where will also accept a hash condition, in which the keys are fields and the values are values to be searched for.

Fields can be symbols or strings. Values can be single values, arrays, or ranges.

User.where({ name: "Joe", email: "[email protected]" })
# SELECT * FROM users WHERE name = 'Joe' AND email = '[email protected]'

User.where({ name: ["Alice", "Bob"]})
# SELECT * FROM users WHERE name IN ('Alice', 'Bob')

User.where({ created_at: (Time.now.midnight - 1.day)..Time.now.midnight })
# SELECT * FROM users WHERE (created_at BETWEEN '2012-06-09 07:00:00.000000' AND '2012-06-10 07:00:00.000000')

In the case of a belongs_to relationship, an association key can be used to specify the model if an ActiveRecord object is used as the value.

author = Author.find(1)

# The following queries will be equivalent:
Post.where(author: author)
Post.where(author_id: author)

This also works with polymorphic belongs_to relationships:

treasure = Treasure.create(name: 'gold coins')
treasure.price_estimates << PriceEstimate.create(price: 125)

# The following queries will be equivalent:
PriceEstimate.where(estimate_of: treasure)
PriceEstimate.where(estimate_of_type: 'Treasure', estimate_of_id: treasure)

Joins

If the relation is the result of a join, you may create a condition which uses any of the tables in the join. For string and array conditions, use the table name in the condition.

User.joins(:posts).where("posts.created_at < ?", Time.now)

For hash conditions, you can either use the table name in the key, or use a sub-hash.

User.joins(:posts).where({ "posts.published" => true })
User.joins(:posts).where({ posts: { published: true } })

no argument

If no argument is passed, #where returns a new instance of WhereChain, that can be chained with #not to return a new relation that negates the where clause.

User.where.not(name: "Jon")
# SELECT * FROM users WHERE name != 'Jon'

See WhereChain for more details on #not.

blank condition

If the condition is any blank-ish object, then #where is a no-op and returns the current relation.


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 675

def where(opts = :chain, *rest)
  if :chain == opts
    WhereChain.new(spawn)
  elsif opts.blank?
    self
  else
    spawn.where!(opts, *rest)
  end
end

#where!(opts, *rest) ⇒ Object

:nodoc:


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# File 'activerecord/lib/active_record/relation/query_methods.rb', line 685

def where!(opts, *rest) # :nodoc:
  opts = sanitize_forbidden_attributes(opts)
  references!(PredicateBuilder.references(opts)) if Hash === opts
  self.where_clause += where_clause_factory.build(opts, rest)
  self
end