Module: ActiveRecord::QueryMethods
Relationships & Source Files | |
Namespace Children | |
Classes:
| |
Extension / Inclusion / Inheritance Descendants | |
Included In:
ActiveRecord::AssociationRelation,
Associations::CollectionProxy ,
ActiveRecord::DisableJoinsAssociationRelation,
Relation
| |
Defined in: | activerecord/lib/active_record/relation/query_methods.rb |
Constant Summary
-
FROZEN_EMPTY_ARRAY =
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 140[].freeze
-
FROZEN_EMPTY_HASH =
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 141{}.freeze
-
VALID_UNSCOPING_VALUES =
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 667Set.new([:where, :select, :group, :order, :lock, :limit, :offset, :joins, :left_outer_joins, :annotate, :includes, :eager_load, :preload, :from, :readonly, :having, :optimizer_hints])
Instance Method Summary
-
#and(other)
Returns a new relation, which is the logical intersection of this relation and the one passed as an argument.
-
#annotate(*args)
Adds an SQL comment to queries generated from this relation.
-
#create_with(value)
Sets attributes to be used when creating new records from a relation object.
-
#distinct(value = true)
Specifies whether the records should be unique or not.
-
#eager_load(*args)
Specify associations
args
to be eager loaded using aLEFT OUTER JOIN
. -
#excluding(*records)
(also: #without)
Excludes the specified record (or collection of records) from the resulting relation.
-
#extending(*modules, &block)
Used to extend a scope with additional methods, either through a module or through a block provided.
- #extensions
-
#extract_associated(association)
Extracts a named
association
from the relation. -
#from(value, subquery_name = nil)
Specifies the table from which the records will be fetched.
-
#group(*args)
Allows to specify a group attribute:
-
#having(opts, *rest)
Allows to specify a HAVING clause.
-
#in_order_of(column, values)
Allows to specify an order by a specific set of values.
-
#includes(*args)
Specify associations
args
to be eager loaded to prevent N + 1 queries. -
#invert_where
Allows you to invert an entire where clause instead of manually applying conditions.
-
#joins(*args)
Performs JOINs on
args
. -
#left_joins(*args)
Alias for #left_outer_joins.
-
#left_outer_joins(*args)
(also: #left_joins)
Performs LEFT OUTER JOINs on
args
: -
#limit(value)
Specifies a limit for the number of records to retrieve.
-
#lock(locks = true)
Specifies locking settings (default to
true
). -
#none
Returns a chainable relation with zero records.
-
#offset(value)
Specifies the number of rows to skip before returning rows.
-
#optimizer_hints(*args)
Specify optimizer hints to be used in the SELECT statement.
-
#or(other)
Returns a new relation, which is the logical union of this relation and the one passed as an argument.
-
#order(*args)
Applies an
ORDER BY
clause to a query. -
#preload(*args)
Specify associations
args
to be eager loaded using separate queries. -
#readonly(value = true)
Mark a relation as readonly.
-
#references(*table_names)
Use to indicate that the given
table_names
are referenced by an SQL string, and should therefore beJOIN
ed in any query rather than loaded separately. -
#regroup(*args)
Allows you to change a previously set group statement.
-
#reorder(*args)
Replaces any existing order defined on the relation with the specified order.
-
#reselect(*args)
Allows you to change a previously set select statement.
-
#reverse_order
Reverse the existing order clause on the relation.
-
#rewhere(conditions)
Allows you to change a previously set where condition for a given attribute, instead of appending to that condition.
-
#select(*fields)
Works in two unique ways.
-
#strict_loading(value = true)
Sets the returned relation to strict_loading mode.
- #structurally_compatible?(other) ⇒ Boolean
-
#uniq!(name)
Deduplicate multiple values.
-
#unscope(*args)
Removes an unwanted relation that is already defined on a chain of relations.
-
#where(*args)
Returns a new relation, which is the result of filtering the current relation according to the conditions in the arguments.
-
#with(*args)
Add a Common Table Expression (CTE) that you can then reference within another SELECT statement.
-
#without(*records)
Alias for #excluding.
Instance Method Details
#and(other)
Returns a new relation, which is the logical intersection 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).
Post.where(id: [1, 2]).and(Post.where(id: [2, 3]))
# SELECT {posts}.* FROM {posts} WHERE {posts}.`id` IN (1, 2) AND {posts}.`id` IN (2, 3)
#annotate(*args)
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.
Some escaping is performed, however untrusted user input should not be used.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1428
def annotate(*args) check_if_method_has_arguments!(__callee__, args) spawn.annotate!(*args) end
#create_with(value)
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'
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1245
def create_with(value) spawn.create_with!(value) end
#distinct(value = true)
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1309
def distinct(value = true) spawn.distinct!(value) end
#eager_load(*args)
Specify associations args
to be eager loaded using a LEFT OUTER JOIN
. Performs a single query joining all specified associations. For example:
users = User.eager_load(:address).limit(5)
users.each do |user|
user.address.city
end
# SELECT "users"."id" AS t0_r0, "users"."name" AS t0_r1, ... FROM "users"
# LEFT OUTER JOIN "addresses" ON "addresses"."id" = "users"."address_id"
# LIMIT 5
Instead of loading the 5 addresses with 5 separate queries, all addresses are loaded with a single joined query.
Loading multiple and nested associations is possible using Hashes and Arrays, similar to #includes:
User.eager_load(:address, friends: [:address, :followers])
# SELECT "users"."id" AS t0_r0, "users"."name" AS t0_r1, ... FROM "users"
# LEFT OUTER JOIN "addresses" ON "addresses"."id" = "users"."address_id"
# LEFT OUTER JOIN "friends" ON "friends"."user_id" = "users"."id"
# ...
NOTE: Loading the associations in a join can result in many rows that contain redundant data and it performs poorly at scale.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 267
def eager_load(*args) check_if_method_has_arguments!(__callee__, args) spawn.eager_load!(*args) end
#excluding(*records) Also known as: #without
Excludes the specified record (or collection of records) from the resulting relation. For example:
Post.excluding(post)
# SELECT "posts".* FROM "posts" WHERE "posts"."id" != 1
Post.excluding(post_one, post_two)
# SELECT "posts".* FROM "posts" WHERE "posts"."id" NOT IN (1, 2)
This can also be called on associations. As with the above example, either a single record of collection thereof may be specified:
post = Post.find(1)
comment = Comment.find(2)
post.comments.excluding(comment)
# SELECT "comments".* FROM "comments" WHERE "comments"."post_id" = 1 AND "comments"."id" != 2
This is short-hand for .where.not(id: post.id)
and .where.not(id: [post_one.id, post_two.id])
.
An ArgumentError
will be raised if either no records are specified, or if any of the records in the collection (if a collection is passed in) are not instances of the same model that the relation is scoping.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1470
def excluding(*records) records.flatten!(1) records.compact! unless records.all?(klass) raise ArgumentError, "You must only pass a single or collection of #{klass.name} objects to ##{__callee__}." end spawn.excluding!(records) end
#extending(*modules, &block)
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
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1355
def extending(*modules, &block) if modules.any? || block spawn.extending!(*modules, &block) else self end end
#extensions
[ GitHub ]# File 'activerecord/lib/active_record/relation/query_methods.rb', line 166
alias extensions extending_values
#extract_associated(association)
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:
account.memberships.extract_associated(:user)
# => Returns collection of User records
This is short-hand for:
account.memberships.preload(:user).collect(&:user)
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 318
def extract_associated(association) preload(association).collect(&association) end
#from(value, subquery_name = nil)
Specifies the 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
Passing a second argument (string or symbol), creates the alias for the SQL from clause. Otherwise the alias “subquery” is used:
Topic.select('a.title').from(Topic.approved, :a)
# SELECT a.title FROM (SELECT * FROM topics WHERE approved = 't') a
It does not add multiple arguments to the SQL from clause. The last from
chained is the one used:
Topic.select('title').from(Topic.approved).from(Topic.inactive)
# SELECT title FROM (SELECT topics.* FROM topics WHERE topics.active = 'f') subquery
For multiple arguments for the SQL from clause, you can pass a string with the exact elements in the SQL from list:
color = "red"
Color
.from("colors c, JSONB_ARRAY_ELEMENTS(colored_things) AS colorvalues(colorvalue)")
.where("colorvalue->>'color' = ?", color)
.select("c.*").to_a
# SELECT c.*
# FROM colors c, JSONB_ARRAY_ELEMENTS(colored_things) AS colorvalues(colorvalue)
# WHERE (colorvalue->>'color' = 'red')
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1290
def from(value, subquery_name = nil) spawn.from!(value, subquery_name) end
#group(*args)
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">]
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 512
def group(*args) check_if_method_has_arguments!(__callee__, args) spawn.group!(*args) end
#having(opts, *rest)
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')
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1096
def having(opts, *rest) opts.blank? ? self : spawn.having!(opts, *rest) end
#in_order_of(column, values)
Allows to specify an order by a specific set of values.
User.in_order_of(:id, [1, 5, 3])
# SELECT "users".* FROM "users"
# WHERE "users"."id" IN (1, 5, 3)
# ORDER BY CASE
# WHEN "users"."id" = 1 THEN 1
# WHEN "users"."id" = 5 THEN 2
# WHEN "users"."id" = 3 THEN 3
# END ASC
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 620
def in_order_of(column, values) klass.disallow_raw_sql!([column], permit: connection.column_name_with_order_matcher) return spawn.none! if values.empty? references = column_references([column]) self.references_values |= references unless references.empty? values = values.map { |value| type_caster.type_cast_for_database(column, value) } arel_column = column.is_a?(Arel::Nodes::SqlLiteral) ? column : order_column(column.to_s) where_clause = if values.include?(nil) arel_column.in(values.compact).or(arel_column.eq(nil)) else arel_column.in(values) end spawn .order!(build_case_for_value_position(arel_column, values)) .where!(where_clause) end
#includes(*args)
Specify associations args
to be eager loaded to prevent N + 1 queries. A separate query is performed for each association, unless a join is required by conditions.
For example:
users = User.includes(:address).limit(5)
users.each do |user|
user.address.city
end
# SELECT "users".* FROM "users" LIMIT 5
# SELECT "addresses".* FROM "addresses" WHERE "addresses"."id" IN (1,2,3,4,5)
Instead of loading the 5 addresses with 5 separate queries, all addresses are loaded with a single query.
Loading the associations in a separate query will often result in a performance improvement over a simple join, as a join can result in many rows that contain redundant data and it performs poorly at scale.
You can also specify multiple associations. Each association will result in an additional query:
User.includes(:address, :friends).to_a
# SELECT "users".* FROM "users"
# SELECT "addresses".* FROM "addresses" WHERE "addresses"."id" IN (1,2,3,4,5)
# SELECT "friends".* FROM "friends" WHERE "friends"."user_id" IN (1,2,3,4,5)
Loading nested associations is possible using a ::Hash
:
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').to_a
Will throw an error, but this will work:
User.includes(:posts).where('posts.name = ?', 'example').references(:posts).to_a
# SELECT "users"."id" AS t0_r0, ... FROM "users"
# LEFT OUTER JOIN "posts" ON "posts"."user_id" = "users"."id"
# WHERE "posts"."name" = ? [["name", "example"]]
As the LEFT OUTER JOIN
already contains the posts, the second query for the posts is no longer performed.
Note that #includes
works with association names while #references needs the actual table name.
If you pass the conditions via a ::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' })
NOTE: Conditions affect both sides of an association. For example, the above code will return only users that have a post named “example”, and will only include posts named “example”, even when a matching user has other additional posts.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 231
def includes(*args) check_if_method_has_arguments!(__callee__, args) spawn.includes!(*args) end
#invert_where
Allows you to invert an entire where clause instead of manually applying conditions.
class User
scope :active, -> { where(accepted: true, locked: false) }
end
User.where(accepted: true)
# WHERE {accepted} = 1
User.where(accepted: true).invert_where
# WHERE {accepted} != 1
User.active
# WHERE {accepted} = 1 AND {locked} = 0
User.active.invert_where
# WHERE NOT (`accepted` = 1 AND {locked} = 0)
Be careful because this inverts all conditions before invert_where
call.
class User
scope :active, -> { where(accepted: true, locked: false) }
scope :inactive, -> { active.invert_where } # Do not attempt it
end
# It also inverts `where(role: 'admin')` unexpectedly.
User.where(role: 'admin').inactive
# WHERE NOT (`role` = 'admin' AND {accepted} = 1 AND {locked} = 0)
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1000
def invert_where spawn.invert_where! end
#joins(*args)
Performs 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" ON "comments"."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
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 767
def joins(*args) check_if_method_has_arguments!(__callee__, args) spawn.joins!(*args) end
#left_joins(*args)
Alias for #left_outer_joins.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 786
alias :left_joins :left_outer_joins
#left_outer_joins(*args) Also known as: #left_joins
Performs LEFT OUTER JOINs on args
:
User.left_outer_joins(:posts)
# SELECT "users".* FROM "users" LEFT OUTER JOIN "posts" ON "posts"."user_id" = "users"."id"
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 782
def left_outer_joins(*args) check_if_method_has_arguments!(__callee__, args) spawn.left_outer_joins!(*args) end
#limit(value)
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'
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1110
def limit(value) spawn.limit!(value) end
#lock(locks = true)
Specifies locking settings (default to true
). For more information on locking, please see Locking
.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1137
def lock(locks = true) spawn.lock!(locks) end
#none
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
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1180
def none spawn.none! end
#offset(value)
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")
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1126
def offset(value) spawn.offset!(value) end
#optimizer_hints(*args)
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"
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1384
def optimizer_hints(*args) check_if_method_has_arguments!(__callee__, args) spawn.optimizer_hints!(*args) end
#or(other)
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).
Post.where("id = 1").or(Post.where("author_id = 3"))
# SELECT {posts}.* FROM {posts} WHERE ((id = 1) OR (author_id = 3))
#order(*args)
Applies an ORDER BY
clause to a query.
#order
accepts arguments in one of several formats.
symbols
The symbol represents the name of the column you want to order the results by.
User.order(:name)
# SELECT "users".* FROM "users" ORDER BY "users"."name" ASC
By default, the order is ascending. If you want descending order, you can map the column name symbol to :desc
.
User.order(email: :desc)
# SELECT "users".* FROM "users" ORDER BY "users"."email" DESC
Multiple columns can be passed this way, and they will be applied in the order specified.
User.order(:name, email: :desc)
# SELECT "users".* FROM "users" ORDER BY "users"."name" ASC, "users"."email" DESC
strings
Strings are passed directly to the database, allowing you to specify simple SQL expressions.
This could be a source of SQL injection, so only strings composed of plain column names and simple function(column_name)
expressions with optional ASC+/+DESC
modifiers are allowed.
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
Arel
If you need to pass in complicated expressions that you have verified are safe for the database, you can use ::Arel
.
User.order(Arel.sql('end_date - start_date'))
# SELECT "users".* FROM "users" ORDER BY end_date - start_date
Custom query syntax, like JSON columns for PostgreSQL, is supported in this way.
User.order(Arel.sql("payload->>'kind'"))
# SELECT "users".* FROM "users" ORDER BY payload->>'kind'
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 595
def order(*args) check_if_method_has_arguments!(__callee__, args) do sanitize_order_arguments(args) end spawn.order!(*args) end
#preload(*args)
Specify associations args
to be eager loaded using separate queries. A separate query is performed for each association.
users = User.preload(:address).limit(5)
users.each do |user|
user.address.city
end
# SELECT "users".* FROM "users" LIMIT 5
# SELECT "addresses".* FROM "addresses" WHERE "addresses"."id" IN (1,2,3,4,5)
Instead of loading the 5 addresses with 5 separate queries, all addresses are loaded with a separate query.
Loading multiple and nested associations is possible using Hashes and Arrays, similar to #includes:
User.preload(:address, friends: [:address, :followers])
# SELECT "users".* FROM "users"
# SELECT "addresses".* FROM "addresses" WHERE "addresses"."id" IN (1,2,3,4,5)
# SELECT "friends".* FROM "friends" WHERE "friends"."user_id" IN (1,2,3,4,5)
# SELECT ...
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 299
def preload(*args) check_if_method_has_arguments!(__callee__, args) spawn.preload!(*args) end
#readonly(value = true)
Mark a relation as readonly. Attempting to update a record will result in an error.
users = User.readonly
users.first.save
#=> ActiveRecord::ReadOnlyRecord: User is marked as readonly
To make a readonly relation writable, pass false
.
users.readonly(false)
users.first.save
#=> true
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1208
def readonly(value = true) spawn.readonly!(value) end
#references(*table_names)
Use to indicate that the given table_names
are referenced by an SQL string, and should therefore be JOIN
ed 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
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 332
def references(*table_names) check_if_method_has_arguments!(__callee__, table_names) spawn.references!(*table_names) end
#regroup(*args)
Allows you to change a previously set group statement.
Post.group(:title, :body)
# SELECT {posts}.`*` FROM {posts} GROUP BY {posts}.`title`, {posts}.`body`
Post.group(:title, :body).regroup(:title)
# SELECT {posts}.`*` FROM {posts} GROUP BY {posts}.`title`
This is short-hand for unscope(:group).group(fields)
. Note that we’re unscoping the entire group statement.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 532
def regroup(*args) check_if_method_has_arguments!(__callee__, args) spawn.regroup!(*args) end
#reorder(*args)
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
.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 651
def reorder(*args) check_if_method_has_arguments!(__callee__, args) do sanitize_order_arguments(args) end spawn.reorder!(*args) end
#reselect(*args)
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.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 480
def reselect(*args) check_if_method_has_arguments!(__callee__, args) args = process_select_args(args) spawn.reselect!(*args) end
#reverse_order
Reverse the existing order clause on the relation.
User.order('name ASC').reverse_order # generated SQL has 'ORDER BY name DESC'
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1397
def reverse_order spawn.reverse_order! end
#rewhere(conditions)
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.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 960
def rewhere(conditions) return unscope(:where) if conditions.nil? scope = spawn where_clause = scope.build_where_clause(conditions) scope.unscope!(where: where_clause.extract_attributes) scope.where_clause += where_clause scope end
#select(*fields)
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 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">]
The argument also can be a hash of fields and aliases.
Model.select(models: { field: :alias, other_field: :other_alias })
# => [#<Model id: nil, alias: "value", other_alias: "value">]
Model.select(models: [:field, :other_field])
# => [#<Model id: nil, field: "value", other_field: "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_one: "value", field_two: "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' for Model
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 390
def select(*fields) if block_given? if fields.any? raise ArgumentError, "`select' with block doesn't take arguments." end return super() end check_if_method_has_arguments!(__callee__, fields, "Call `select' with at least one field.") fields = process_select_args(fields) spawn._select!(*fields) end
#strict_loading(value = true)
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
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1223
def strict_loading(value = true) spawn.strict_loading!(value) end
#structurally_compatible?(other) ⇒ Boolean
Checks whether the given relation is structurally compatible with this relation, to determine if it’s possible to use the #and and #or methods without raising an error. Structurally compatible is defined as: 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).
Post.where("id = 1").structurally_compatible?(Post.where("author_id = 3"))
# => true
Post.joins(:comments).structurally_compatible?(Post.where("id = 1"))
# => false
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1020
def structurally_compatible?(other) structurally_incompatible_values_for(other).empty? end
#uniq!(name)
Deduplicate multiple values.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1440
def uniq!(name) if values = @values[name] values.uniq! if values.is_a?(Array) && !values.empty? end self end
#unscope(*args)
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) }
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 705
def unscope(*args) check_if_method_has_arguments!(__callee__, args) spawn.unscope!(*args) end
#where(*args)
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", "joe@example.com"])
# SELECT * FROM users WHERE name = 'Joe' AND email = 'joe@example.com';
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: "joe@example.com" }])
# SELECT * FROM users WHERE name = 'Joe' AND email = 'joe@example.com';
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", "joe@example.com"])
# SELECT * FROM users WHERE name = 'Joe' AND email = 'joe@example.com';
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: "joe@example.com" })
# SELECT * FROM users WHERE name = 'Joe' AND email = 'joe@example.com';
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: "joe@example.com")
# SELECT * FROM users WHERE name = 'Joe' AND email = 'joe@example.com'
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.find(1)
# The following queries will be equivalent:
Post.where(author: )
Post.where(author_id: )
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)
::Hash
conditions may also be specified in a tuple-like syntax. ::Hash
keys may be an array of columns with an array of tuples as values.
Article.where([:, :id] => [[15, 1], [15, 2]])
# SELECT * FROM articles WHERE author_id = 15 AND id = 1 OR author_id = 15 AND id = 2
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 QueryMethods::WhereChain
, that can be chained with WhereChain#not, WhereChain#missing, or WhereChain#associated.
Chaining with WhereChain#not:
User.where.not(name: "Jon")
# SELECT * FROM users WHERE name != 'Jon'
Chaining with WhereChain#associated:
Post.where.associated(: )
# SELECT "posts".* FROM "posts"
# INNER JOIN "authors" ON "authors"."id" = "posts"."author_id"
# WHERE "authors"."id" IS NOT NULL
Chaining with WhereChain#missing:
Post.where.missing(: )
# SELECT "posts".* FROM "posts"
# LEFT OUTER JOIN "authors" ON "authors"."id" = "posts"."author_id"
# WHERE "authors"."id" IS NULL
Blank Condition
If the condition is any blank-ish object, then #where
is a no-op and returns the current relation.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 932
def where(*args) if args.empty? WhereChain.new(spawn) elsif args.length == 1 && args.first.blank? self else spawn.where!(*args) end end
#with(*args)
Add a Common Table Expression (CTE) that you can then reference within another SELECT statement.
Note: CTE’s are only supported in MySQL for versions 8.0 and above. You will not be able to use CTE’s with MySQL 5.7.
Post.with(posts_with_tags: Post.where("tags_count > ?", 0))
# => ActiveRecord::Relation
# WITH posts_with_tags AS (
# SELECT * FROM posts WHERE (tags_count > 0)
# )
# SELECT * FROM posts
Once you define Common Table Expression you can use custom FROM
value or JOIN
to reference it.
Post.with(posts_with_tags: Post.where("tags_count > ?", 0)).from("posts_with_tags AS posts")
# => ActiveRecord::Relation
# WITH posts_with_tags AS (
# SELECT * FROM posts WHERE (tags_count > 0)
# )
# SELECT * FROM posts_with_tags AS posts
Post.with(posts_with_tags: Post.where("tags_count > ?", 0)).joins("JOIN posts_with_tags ON posts_with_tags.id = posts.id")
# => ActiveRecord::Relation
# WITH posts_with_tags AS (
# SELECT * FROM posts WHERE (tags_count > 0)
# )
# SELECT * FROM posts JOIN posts_with_tags ON posts_with_tags.id = posts.id
It is recommended to pass a query as Relation
. If that is not possible and you have verified it is safe for the database, you can pass it as SQL literal using ::Arel
.
Post.with(popular_posts: Arel.sql("... complex sql to calculate posts popularity ..."))
Great caution should be taken to avoid SQL injection vulnerabilities. This method should not be used with unsafe values that include unsanitized input.
To add multiple CTEs just pass multiple key-value pairs
Post.with(
posts_with_comments: Post.where("comments_count > ?", 0),
posts_with_tags: Post.where("tags_count > ?", 0)
)
or chain multiple #with
calls
Post
.with(posts_with_comments: Post.where("comments_count > ?", 0))
.with(posts_with_tags: Post.where("tags_count > ?", 0))
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 459
def with(*args) check_if_method_has_arguments!(__callee__, args) spawn.with!(*args) end
#without(*records)
Alias for #excluding.
# File 'activerecord/lib/active_record/relation/query_methods.rb', line 1480
alias :without :excluding