Active Record Relation

Namespace

Module

Methods

Included Modules

Constants

CLAUSE_METHODS = [:where, :having, :from]
INVALID_METHODS_FOR_DELETE_ALL = [:distinct, :group, :having]
MULTI_VALUE_METHODS = [:includes, :eager_load, :preload, :select, :group, :order, :joins, :left_outer_joins, :references, :extending, :unscope]
SINGLE_VALUE_METHODS = [:limit, :offset, :lock, :readonly, :reordering, :reverse_order, :distinct, :create_with, :skip_query_cache]
VALUE_METHODS = MULTI_VALUE_METHODS + SINGLE_VALUE_METHODS + CLAUSE_METHODS

Attributes

[R] klass
[R] loaded
[R] loaded?
[R] model
[R] predicate_builder
[R] table

Class Public methods

new(klass, table: klass.arel_table, predicate_builder: klass.predicate_builder, values: {})

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 25
    def initialize(klass, table: klass.arel_table, predicate_builder: klass.predicate_builder, values: {})
      @klass  = klass
      @table  = table
      @values = values
      @offsets = {}
      @loaded = false
      @predicate_builder = predicate_builder
      @delegate_to_klass = false
    end
πŸ”Ž See on GitHub

Instance Public methods

==(other)

Compares two relations for equality.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 487
    def ==(other)
      case other
      when Associations::CollectionProxy, AssociationRelation
        self == other.records
      when Relation
        other.to_sql == to_sql
      when Array
        records == other
      end
    end
πŸ”Ž See on GitHub

any?()

Returns true if there are any records.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 227
    def any?
      return super if block_given?
      !empty?
    end
πŸ”Ž See on GitHub

blank?()

Returns true if relation is blank.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 503
    def blank?
      records.blank?
    end
πŸ”Ž See on GitHub

build(attributes = nil, &block)

Alias for: new

cache_key(timestamp_column = :updated_at)

Returns a cache key that can be used to identify the records fetched by this query. The cache key is built with a fingerprint of the sql query, the number of records matched by the query and a timestamp of the last updated record. When a new record comes to match the query, or any of the existing records is updated or deleted, the cache key changes.

Product.where("name like ?", "%Cosmic Encounter%").cache_key
# => "products/query-1850ab3d302391b85b8693e941286659-1-20150714212553907087000"

If the collection is loaded, the method will iterate through the records to generate the timestamp, otherwise it will trigger one SQL query like:

SELECT COUNT(*), MAX("products"."updated_at") FROM "products" WHERE (name like '%Cosmic Encounter%')

You can also pass a custom timestamp column to fetch the timestamp of the last updated record.

Product.where("name like ?", "%Game%").cache_key(:last_reviewed_at)

You can customize the strategy to generate the key on a per model basis overriding ActiveRecord::Base#collection_cache_key.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 265
    def cache_key(timestamp_column = :updated_at)
      @cache_keys ||= {}
      @cache_keys[timestamp_column] ||= @klass.collection_cache_key(self, timestamp_column)
    end
πŸ”Ž See on GitHub

create(attributes = nil, &block)

Tries to create a new record with the same scoped attributes defined in the relation. Returns the initialized object if validation fails.

Expects arguments in the same format as ActiveRecord::Base.create.

Examples

users = User.where(name: 'Oscar')
users.create # => #<User id: 3, name: "Oscar", ...>

users.create(name: 'fxn')
users.create # => #<User id: 4, name: "fxn", ...>

users.create { |user| user.name = 'tenderlove' }
# => #<User id: 5, name: "tenderlove", ...>

users.create(name: nil) # validation on name
# => #<User id: nil, name: nil, ...>
πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 81
    def create(attributes = nil, &block)
      if attributes.is_a?(Array)
        attributes.collect { |attr| create(attr, &block) }
      else
        scoping { klass.create(values_for_create(attributes), &block) }
      end
    end
πŸ”Ž See on GitHub

create!(attributes = nil, &block)

Similar to create, but calls create! on the base class. Raises an exception if a validation error occurs.

Expects arguments in the same format as ActiveRecord::Base.create!.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 95
    def create!(attributes = nil, &block)
      if attributes.is_a?(Array)
        attributes.collect { |attr| create!(attr, &block) }
      else
        scoping { klass.create!(values_for_create(attributes), &block) }
      end
    end
πŸ”Ž See on GitHub

delete_all()

Deletes the records without instantiating the records first, and hence not calling the #destroy method nor invoking callbacks. This is a single SQL DELETE statement that goes straight to the database, much more efficient than destroy_all. Be careful with relations though, in particular :dependent rules defined on associations are not honored. Returns the number of rows affected.

Post.where(person_id: 5).where(category: ['Something', 'Else']).delete_all

Both calls delete the affected posts all at once with a single DELETE statement. If you need to destroy dependent associations or call your before_* or after_destroy callbacks, use the destroy_all method instead.

If an invalid method is supplied, delete_all raises an ActiveRecordError:

Post.distinct.delete_all
# => ActiveRecord::ActiveRecordError: delete_all doesn't support distinct
πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 386
    def delete_all
      invalid_methods = INVALID_METHODS_FOR_DELETE_ALL.select do |method|
        value = get_value(method)
        SINGLE_VALUE_METHODS.include?(method) ? value : value.any?
      end
      if invalid_methods.any?
        raise ActiveRecordError.new("delete_all doesn't support #{invalid_methods.join(', ')}")
      end

      if eager_loading?
        relation = apply_join_dependency
        return relation.delete_all
      end

      stmt = Arel::DeleteManager.new
      stmt.from(table)

      if has_join_values? || has_limit_or_offset?
        @klass.connection.join_to_delete(stmt, arel, arel_attribute(primary_key))
      else
        stmt.wheres = arel.constraints
      end

      affected = @klass.connection.delete(stmt, "#{@klass} Destroy")

      reset
      affected
    end
πŸ”Ž See on GitHub

destroy_all()

Destroys the records by instantiating each record and calling its #destroy method. Each object's callbacks are executed (including :dependent association options). Returns the collection of objects that were destroyed; each will be frozen, to reflect that no changes should be made (since they can't be persisted).

Note: Instantiation, callback execution, and deletion of each record can be time consuming when you're removing many records at once. It generates at least one SQL DELETE query per record (or possibly more, to enforce your callbacks). If you want to delete many rows quickly, without concern for their associations or callbacks, use delete_all instead.

Examples

Person.where(age: 0..18).destroy_all
πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 364
    def destroy_all
      records.each(&:destroy).tap { reset }
    end
πŸ”Ž See on GitHub

eager_loading?()

Returns true if relation needs eager loading.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 472
    def eager_loading?
      @should_eager_load ||=
        eager_load_values.any? ||
        includes_values.any? && (joined_includes_values.any? || references_eager_loaded_tables?)
    end
πŸ”Ž See on GitHub

empty?()

Returns true if there are no records.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 215
    def empty?
      return @records.empty? if loaded?
      !exists?
    end
πŸ”Ž See on GitHub

encode_with(coder)

Serializes the relation objects Array.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 205
    def encode_with(coder)
      coder.represent_seq(nil, records)
    end
πŸ”Ž See on GitHub

explain()

Runs EXPLAIN on the query or queries triggered by this relation and returns the result as a string. The string is formatted imitating the ones printed by the database shell.

Note that this method actually runs the queries, since the results of some are needed by the next ones when eager loading is going on.

Please see further details in the Active Record Query Interface guide.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 189
    def explain
      exec_explain(collecting_queries_for_explain { exec_queries })
    end
πŸ”Ž See on GitHub

find_or_create_by(attributes, &block)

Finds the first record with the given attributes, or creates a record with the attributes if one is not found:

# Find the first user named "PenΓ©lope" or create a new one.
User.find_or_create_by(first_name: 'PenΓ©lope')
# => #<User id: 1, first_name: "PenΓ©lope", last_name: nil>

# Find the first user named "PenΓ©lope" or create a new one.
# We already have one so the existing record will be returned.
User.find_or_create_by(first_name: 'PenΓ©lope')
# => #<User id: 1, first_name: "PenΓ©lope", last_name: nil>

# Find the first user named "Scarlett" or create a new one with
# a particular last name.
User.create_with(last_name: 'Johansson').find_or_create_by(first_name: 'Scarlett')
# => #<User id: 2, first_name: "Scarlett", last_name: "Johansson">

This method accepts a block, which is passed down to create. The last example above can be alternatively written this way:

# Find the first user named "Scarlett" or create a new one with a
# different last name.
User.find_or_create_by(first_name: 'Scarlett') do |user|
  user.last_name = 'Johansson'
end
# => #<User id: 2, first_name: "Scarlett", last_name: "Johansson">

This method always returns a record, but if creation was attempted and failed due to validation errors it won't be persisted, you get what create returns in such situation.

Please note *this method is not atomic*, it runs first a SELECT, and if there are no results an INSERT is attempted. If there are other threads or processes there is a race condition between both calls and it could be the case that you end up with two similar records.

Whether that is a problem or not depends on the logic of the application, but in the particular case in which rows have a UNIQUE constraint an exception may be raised, just retry:

begin
  CreditAccount.transaction(requires_new: true) do
    CreditAccount.find_or_create_by(user_id: user.id)
  end
rescue ActiveRecord::RecordNotUnique
  retry
end
πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 163
    def find_or_create_by(attributes, &block)
      find_by(attributes) || create(attributes, &block)
    end
πŸ”Ž See on GitHub

find_or_create_by!(attributes, &block)

Like find_or_create_by, but calls create! so an exception is raised if the created record is invalid.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 170
    def find_or_create_by!(attributes, &block)
      find_by(attributes) || create!(attributes, &block)
    end
πŸ”Ž See on GitHub

find_or_initialize_by(attributes, &block)

Like find_or_create_by, but calls new instead of create.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 176
    def find_or_initialize_by(attributes, &block)
      find_by(attributes) || new(attributes, &block)
    end
πŸ”Ž See on GitHub

initialize_copy(other)

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 35
    def initialize_copy(other)
      @values = @values.dup
      reset
    end
πŸ”Ž See on GitHub

inspect()

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 511
    def inspect
      subject = loaded? ? records : self
      entries = subject.take([limit_value, 11].compact.min).map!(&:inspect)

      entries[10] = "..." if entries.size == 11

      "#<#{self.class.name} [#{entries.join(', ')}]>"
    end
πŸ”Ž See on GitHub

joined_includes_values()

Joins that are also marked for preloading. In which case we should just eager load them. Note that this is a naive implementation because we could have strings and symbols which represent the same association, but that aren't matched by this. Also, we could have nested hashes which partially match, e.g. { a: :b } & { a: [:b, :c] }

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 482
    def joined_includes_values
      includes_values & joins_values
    end
πŸ”Ž See on GitHub

load(&block)

Causes the records to be loaded from the database if they have not been loaded already. You can use this if for some reason you need to explicitly load some records before actually using them. The return value is the relation itself, not the records.

Post.where(published: true).load # => #<ActiveRecord::Relation>
πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 421
    def load(&block)
      exec_queries(&block) unless loaded?

      self
    end
πŸ”Ž See on GitHub

many?()

Returns true if there is more than one record.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 239
    def many?
      return super if block_given?
      limit_value ? records.many? : size > 1
    end
πŸ”Ž See on GitHub

new(attributes = nil, &block)

Initializes new record from relation while maintaining the current scope.

Expects arguments in the same format as ActiveRecord::Base.new.

users = User.where(name: 'DHH')
user = users.new # => #<User id: nil, name: "DHH", created_at: nil, updated_at: nil>

You can also pass a block to new with the new record as argument:

user = users.new { |user| user.name = 'Oscar' }
user.name # => Oscar
Also aliased as: build
πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 56
    def new(attributes = nil, &block)
      scoping { klass.new(values_for_create(attributes), &block) }
    end
πŸ”Ž See on GitHub

none?()

Returns true if there are no records.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 221
    def none?
      return super if block_given?
      empty?
    end
πŸ”Ž See on GitHub

one?()

Returns true if there is exactly one record.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 233
    def one?
      return super if block_given?
      limit_value ? records.one? : size == 1
    end
πŸ”Ž See on GitHub

pretty_print(q)

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 498
    def pretty_print(q)
      q.pp(records)
    end
πŸ”Ž See on GitHub

reload()

Forces reloading of relation.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 428
    def reload
      reset
      load
    end
πŸ”Ž See on GitHub

reset()

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 433
    def reset
      @delegate_to_klass = false
      @to_sql = @arel = @loaded = @should_eager_load = nil
      @records = [].freeze
      @offsets = {}
      self
    end
πŸ”Ž See on GitHub

scope_for_create()

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 467
    def scope_for_create
      where_values_hash.merge!(create_with_value.stringify_keys)
    end
πŸ”Ž See on GitHub

scoping()

Scope all queries to the current scope.

Comment.where(post_id: 1).scoping do
  Comment.first
end
# => SELECT "comments".* FROM "comments" WHERE "comments"."post_id" = 1 ORDER BY "comments"."id" ASC LIMIT 1

Please check unscoped if you want to remove all previous scopes (including the default_scope) during the execution of a block.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 279
    def scoping
      previous, klass.current_scope = klass.current_scope(true), self unless @delegate_to_klass
      yield
    ensure
      klass.current_scope = previous unless @delegate_to_klass
    end
πŸ”Ž See on GitHub

size()

Returns size of the records.

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 210
    def size
      loaded? ? @records.length : count(:all)
    end
πŸ”Ž See on GitHub

to_a()

Alias for: to_ary

to_ary()

Converts relation objects to Array.

Also aliased as: to_a
πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 194
    def to_ary
      records.dup
    end
πŸ”Ž See on GitHub

to_sql()

Returns sql statement for the relation.

User.where(name: 'Oscar').to_sql
# => SELECT "users".* FROM "users"  WHERE "users"."name" = 'Oscar'
πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 445
    def to_sql
      @to_sql ||= begin
        if eager_loading?
          apply_join_dependency do |relation, join_dependency|
            relation = join_dependency.apply_column_aliases(relation)
            relation.to_sql
          end
        else
          conn = klass.connection
          conn.unprepared_statement { conn.to_sql(arel) }
        end
      end
    end
πŸ”Ž See on GitHub

update_all(updates)

Updates all records in the current relation with details given. This method constructs a single SQL UPDATE statement and sends it straight to the database. It does not instantiate the involved models and it does not trigger Active Record callbacks or validations. However, values passed to update_all will still go through Active Record's normal type casting and serialization.

Parameters

  • updates - A string, array, or hash representing the SET part of an SQL statement.

Examples

# Update all customers with the given attributes
Customer.update_all wants_email: true

# Update all books with 'Rails' in their title
Book.where('title LIKE ?', '%Rails%').update_all(author: 'David')

# Update all books that match conditions, but limit it to 5 ordered by date
Book.where('title LIKE ?', '%Rails%').order(:created_at).limit(5).update_all(author: 'David')

# Update all invoices and set the number column to its id value.
Invoice.update_all('number = id')
πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 315
    def update_all(updates)
      raise ArgumentError, "Empty list of attributes to change" if updates.blank?

      if eager_loading?
        relation = apply_join_dependency
        return relation.update_all(updates)
      end

      stmt = Arel::UpdateManager.new

      stmt.set Arel.sql(@klass.sanitize_sql_for_assignment(updates))
      stmt.table(table)

      if has_join_values? || offset_value
        @klass.connection.join_to_update(stmt, arel, arel_attribute(primary_key))
      else
        stmt.key = arel_attribute(primary_key)
        stmt.take(arel.limit)
        stmt.order(*arel.orders)
        stmt.wheres = arel.constraints
      end

      @klass.connection.update stmt, "#{@klass} Update All"
    end
πŸ”Ž See on GitHub

values()

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 507
    def values
      @values.dup
    end
πŸ”Ž See on GitHub

where_values_hash(relation_table_name = klass.table_name)

Returns a hash of where conditions.

User.where(name: 'Oscar').where_values_hash
# => {name: "Oscar"}
πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 463
    def where_values_hash(relation_table_name = klass.table_name)
      where_clause.to_h(relation_table_name)
    end
πŸ”Ž See on GitHub

Instance Protected methods

load_records(records)

πŸ“ Source code
# File activerecord/lib/active_record/relation.rb, line 535
      def load_records(records)
        @records = records.freeze
        @loaded = true
      end
πŸ”Ž See on GitHub