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VALID_UNSCOPING_VALUES | = | Set.new([:where, :select, :group, :order, :lock, :limit, :offset, :joins, :includes, :from, :readonly, :having]) |
Returns the Arel object associated with the relation.
Like arel, but ignores the default scope of the model.
# File activerecord/lib/active_record/relation/query_methods.rb, line 801 def build_arel arel = Arel::SelectManager.new(table.engine, table) build_joins(arel, joins_values.flatten) unless joins_values.empty? collapse_wheres(arel, (where_values - ['']).uniq) arel.having(*having_values.uniq.reject{|h| h.blank?}) unless having_values.empty? arel.take(connection.sanitize_limit(limit_value)) if limit_value arel.skip(offset_value.to_i) if offset_value arel.group(*group_values.uniq.reject{|g| g.blank?}) unless group_values.empty? build_order(arel) build_select(arel, select_values.uniq) arel.distinct(distinct_value) arel.from(build_from) if from_value arel.lock(lock_value) if lock_value arel end
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'
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
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"
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
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
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, ...>]
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')
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
.
conditions
If you want to add 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)
Performs a joins on args
:
User.joins(:posts) => SELECT "users".* FROM "users" INNER JOIN "posts" ON "posts"."user_id" = "users"."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
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'
Specifies locking settings (default to true
). For more
information on locking, please see +ActiveRecord::Locking+.
Returns a chainable relation with zero records, specifically an instance of
the ActiveRecord::NullRelation
class.
The returned ActiveRecord::NullRelation
inherits from Relation and 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 # => returning [] instead breaks the previous code end end
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")
Allows to specify an order attribute:
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 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
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)
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: ActiveRecord::ReadOnlyRecord
Used to indicate that an association is referenced by an SQL string, and should therefore be JOINed in any query rather than loaded separately.
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
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’.
Reverse the existing order clause on the relation.
User.order('name ASC').reverse_order # generated SQL has 'ORDER BY name DESC'
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 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 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 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 will throw ActiveModel::MissingAttributeError
:
Model.select(:field).first.other_field # => ActiveModel::MissingAttributeError: missing attribute: other_field
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)
Note that this method is more generalized than ActiveRecord::SpawnMethods#except because except will only affect a particular relation’s values. It won’t wipe the order, grouping, etc. when that relation is merged. For example:
Post.comments.except(:order)
will still have an order if it comes from the default_scope on Comment.
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 a 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 = 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.