class ActiveRecord::Relation - activerecord-4.2.3 Documentation

# class ActiveRecord::Relation

# Active Record Relation¶ ↑

### Constants

INVALID_METHODS_FOR_DELETE_ALL
MULTI_VALUE_METHODS
SINGLE_VALUE_METHODS
VALUE_METHODS

### Attributes

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

### Public Class Methods

new(klass, table, values = {}) click to toggle source

    # File lib/active_record/relation.rb, line 22
    def initialize(klass, table, values = {})
      @klass  = klass
      @table  = table
      @values = values
      @offsets = {}
      @loaded = false
    end

### Public Instance Methods

==(other) click to toggle source

Compares two relations for equality.

    # File lib/active_record/relation.rb, line 603
    def ==(other)
      case other
      when Associations::CollectionProxy, AssociationRelation
        self == other.to_a
      when Relation
        other.to_sql == to_sql
      when Array
        to_a == other
      end
    end

any?() { |*block_args| ... } click to toggle source

Returns true if there are any records.

    # File lib/active_record/relation.rb, line 273
    def any?
      if block_given?
        to_a.any? { |*block_args| yield(*block_args) }
      else
        !empty?
      end
    end

blank?() click to toggle source

Returns true if relation is blank.

    # File lib/active_record/relation.rb, line 619
    def blank?
      to_a.blank?
    end

build(*args, &block)
Alias for: new
create(*args, &block) click to toggle source

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 `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, ...>

    # File lib/active_record/relation.rb, line 141
    def create(*args, &block)
      scoping { @klass.create(*args, &block) }
    end

create!(*args, &block) click to toggle source

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 `Base.create!`.

    # File lib/active_record/relation.rb, line 149
    def create!(*args, &block)
      scoping { @klass.create!(*args, &block) }
    end

delete(id_or_array) click to toggle source

Deletes the row with a primary key matching the `id` argument, using a SQL `DELETE` statement, and returns the number of rows deleted. Active Record objects are not instantiated, so the object's callbacks are not executed, including any `:dependent` association options.

You can delete multiple rows at once by passing an Array of `id`s.

Note: Although it is often much faster than the alternative, `#destroy`, skipping callbacks might bypass business logic in your application that ensures referential integrity or performs other essential jobs.

#### Examples¶ ↑

    # Delete a single row
    Todo.delete(1)

    # Delete multiple rows
    Todo.delete([2,3,4])

    # File lib/active_record/relation.rb, line 502
    def delete(id_or_array)
      where(primary_key => id_or_array).delete_all
    end

delete_all(conditions = nil) click to toggle source

Deletes the records matching `conditions` 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.delete_all("person_id = 5 AND (category = 'Something' OR category = 'Else')")
    Post.delete_all(["person_id = ? AND (category = ? OR category = ?)", 5, 'Something', 'Else'])
    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 ActiveRecord error:

    Post.limit(100).delete_all
    # => ActiveRecord::ActiveRecordError: delete_all doesn't support limit

    # File lib/active_record/relation.rb, line 452
    def delete_all(conditions = nil)
      invalid_methods = INVALID_METHODS_FOR_DELETE_ALL.select { |method|
        if MULTI_VALUE_METHODS.include?(method)
          send("#{method}_values").any?
        else
          send("#{method}_value")
        end
      }
      if invalid_methods.any?
        raise ActiveRecordError.new("delete_all doesn't support #{invalid_methods.join(', ')}")
      end

      if conditions
        where(conditions).delete_all
      else
        stmt = Arel::DeleteManager.new(arel.engine)
        stmt.from(table)

        if joins_values.any?
          @klass.connection.join_to_delete(stmt, arel, table[primary_key])
        else
          stmt.wheres = arel.constraints
        end

        affected = @klass.connection.delete(stmt, 'SQL', bind_values)

        reset
        affected
      end
    end

destroy(id) click to toggle source

Destroy an object (or multiple objects) that has the given id. The object is instantiated first, therefore all callbacks and filters are fired off before the object is deleted. This method is less efficient than ActiveRecord#delete but allows cleanup methods and other actions to be run.

This essentially finds the object (or multiple objects) with the given id, creates a new object from the attributes, and then calls destroy on it.

#### Parameters¶ ↑

- `id` - Can be either an Integer or an Array of Integers.

#### Examples¶ ↑

    # Destroy a single object
    Todo.destroy(1)

    # Destroy multiple objects
    todos = [1,2,3]
    Todo.destroy(todos)

    # File lib/active_record/relation.rb, line 425
    def destroy(id)
      if id.is_a?(Array)
        id.map { |one_id| destroy(one_id) }
      else
        find(id).destroy
      end
    end

destroy_all(conditions = nil) click to toggle source

Destroys the records matching `conditions` 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.

#### Parameters¶ ↑

- `conditions` - A string, array, or hash that specifies which records to destroy. If omitted, all records are destroyed. See the Conditions section in the introduction to ActiveRecord::Base for more information.

#### Examples¶ ↑

    Person.destroy_all("last_login < '2004-04-04'")
    Person.destroy_all(status: "inactive")
    Person.where(age: 0..18).destroy_all

    # File lib/active_record/relation.rb, line 398
    def destroy_all(conditions = nil)
      if conditions
        where(conditions).destroy_all
      else
        to_a.each {|object| object.destroy }.tap { reset }
      end
    end

eager_loading?() click to toggle source

Returns true if relation needs eager loading.

    # File lib/active_record/relation.rb, line 582
    def eager_loading?
      @should_eager_load ||=
        eager_load_values.any? ||
        includes_values.any? && (joined_includes_values.any? || references_eager_loaded_tables?)
    end

empty?() click to toggle source

Returns true if there are no records.

    # File lib/active_record/relation.rb, line 261
    def empty?
      return @records.empty? if loaded?

      if limit_value == 0
        true
      else
        c = count(:all)
        c.respond_to?(:zero?) ? c.zero? : c.empty?
      end
    end

encode_with(coder) click to toggle source

Serializes the relation objects Array.

    # File lib/active_record/relation.rb, line 247
    def encode_with(coder)
      coder.represent_seq(nil, to_a)
    end

explain() click to toggle source

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.

    # File lib/active_record/relation.rb, line 235
    def explain
      #TODO: Fix for binds.
      exec_explain(collecting_queries_for_explain { exec_queries })
    end

find_or_create_by(attributes, &block) click to toggle source

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 "Penélope" or create a new one.
    User.find_or_create_by(first_name: 'Penélope')
    # => #<User id: 1, first_name: "Penélope", last_name: nil>

    # Find the first user named "Penélope" or create a new one.
    # We already have one so the existing record will be returned.
    User.find_or_create_by(first_name: 'Penélope')
    # => #<User id: 1, first_name: "Penélope", 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.find_or_create_by(user_id: user.id)
    rescue ActiveRecord::RecordNotUnique
      retry
    end

    # File lib/active_record/relation.rb, line 211
    def find_or_create_by(attributes, &block)
      find_by(attributes) || create(attributes, &block)
    end

find_or_create_by!(attributes, &block) click to toggle source

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

    # File lib/active_record/relation.rb, line 217
    def find_or_create_by!(attributes, &block)
      find_by(attributes) || create!(attributes, &block)
    end

find_or_initialize_by(attributes, &block) click to toggle source

Like `find_or_create_by`, but calls `new` instead of `create`.

    # File lib/active_record/relation.rb, line 222
    def find_or_initialize_by(attributes, &block)
      find_by(attributes) || new(attributes, &block)
    end

initialize_copy(other) click to toggle source

    # File lib/active_record/relation.rb, line 30
    def initialize_copy(other)
      # This method is a hot spot, so for now, use Hash[] to dup the hash.
      #   https://bugs.ruby-lang.org/issues/7166
      @values        = Hash[@values]
      @values[:bind] = @values[:bind].dup if @values.key? :bind
      reset
    end

inspect() click to toggle source

    # File lib/active_record/relation.rb, line 627
    def inspect
      entries = to_a.take([limit_value, 11].compact.min).map!(&:inspect)
      entries[10] = '...' if entries.size == 11

      "#<#{self.class.name} [#{entries.join(', ')}]>"
    end

joined_includes_values() click to toggle source

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] }

    # File lib/active_record/relation.rb, line 592
    def joined_includes_values
      includes_values & joins_values
    end

load() click to toggle source

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>

    # File lib/active_record/relation.rb, line 512
    def load
      exec_queries unless loaded?

      self
    end

many?() { |*block_args| ... } click to toggle source

Returns true if there is more than one record.

    # File lib/active_record/relation.rb, line 282
    def many?
      if block_given?
        to_a.many? { |*block_args| yield(*block_args) }
      else
        limit_value ? to_a.many? : size > 1
      end
    end

new(*args, &block) click to toggle source

Initializes new record from relation while maintaining the current scope.

Expects arguments in the same format as `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

    # File lib/active_record/relation.rb, line 118
    def new(*args, &block)
      scoping { @klass.new(*args, &block) }
    end

Also aliased as: build
pretty_print(q) click to toggle source

    # File lib/active_record/relation.rb, line 614
    def pretty_print(q)
      q.pp(self.to_a)
    end

reload() click to toggle source

Forces reloading of relation.

    # File lib/active_record/relation.rb, line 519
    def reload
      reset
      load
    end

reset() click to toggle source

    # File lib/active_record/relation.rb, line 524
    def reset
      @last = @to_sql = @order_clause = @scope_for_create = @arel = @loaded = nil
      @should_eager_load = @join_dependency = nil
      @records = []
      @offsets = {}
      self
    end

scope_for_create() click to toggle source

    # File lib/active_record/relation.rb, line 577
    def scope_for_create
      @scope_for_create ||= where_values_hash.merge(create_with_value)
    end

scoping() { || ... } click to toggle source

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.

    # File lib/active_record/relation.rb, line 299
    def scoping
      previous, klass.current_scope = klass.current_scope, self
      yield
    ensure
      klass.current_scope = previous
    end

size() click to toggle source

Returns size of the records.

    # File lib/active_record/relation.rb, line 256
    def size
      loaded? ? @records.length : count(:all)
    end

to_a() click to toggle source

Converts relation objects to Array.

    # File lib/active_record/relation.rb, line 241
    def to_a
      load
      @records
    end

to_sql() click to toggle source

Returns sql statement for the relation.

    User.where(name: 'Oscar').to_sql
    # => SELECT "users".* FROM "users"  WHERE "users"."name" = 'Oscar'

    # File lib/active_record/relation.rb, line 536
    def to_sql
      @to_sql ||= begin
                    relation   = self
                    connection = klass.connection
                    visitor    = connection.visitor

                    if eager_loading?
                      find_with_associations { |rel| relation = rel }
                    end

                    arel  = relation.arel
                    binds = (arel.bind_values + relation.bind_values).dup
                    binds.map! { |bv| connection.quote(*bv.reverse) }
                    collect = visitor.accept(arel.ast, Arel::Collectors::Bind.new)
                    collect.substitute_binds(binds).join
                  end
    end

uniq_value() click to toggle source

`uniq` and `uniq!` are silently deprecated. `uniq_value` delegates to `distinct_value` to maintain backwards compatibility. Use `distinct_value` instead.

    # File lib/active_record/relation.rb, line 598
    def uniq_value
      distinct_value
    end

update(id, attributes) click to toggle source

Updates an object (or multiple objects) and saves it to the database, if validations pass. The resulting object is returned whether the object was saved successfully to the database or not.

#### Parameters¶ ↑

- `id` - This should be the id or an array of ids to be updated.

- `attributes` - This should be a hash of attributes or an array of hashes.

#### Examples¶ ↑

    # Updates one record
    Person.update(15, user_name: 'Samuel', group: 'expert')

    # Updates multiple records
    people = { 1 => { "first_name" => "David" }, 2 => { "first_name" => "Jeremy" } }
    Person.update(people.keys, people.values)

    # File lib/active_record/relation.rb, line 363
    def update(id, attributes)
      if id.is_a?(Array)
        id.map.with_index { |one_id, idx| update(one_id, attributes[idx]) }
      else
        object = find(id)
        object.update(attributes)
        object
      end
    end

update_all(updates) click to toggle source

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. Values passed to `update_all` will not go through ActiveRecord's type-casting behavior. It should receive only values that can be passed as-is to the SQL database.

#### 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')

    # File lib/active_record/relation.rb, line 326
    def update_all(updates)
      raise ArgumentError, "Empty list of attributes to change" if updates.blank?

      stmt = Arel::UpdateManager.new(arel.engine)

      stmt.set Arel.sql(@klass.send(:sanitize_sql_for_assignment, updates))
      stmt.table(table)
      stmt.key = table[primary_key]

      if joins_values.any?
        @klass.connection.join_to_update(stmt, arel)
      else
        stmt.take(arel.limit)
        stmt.order(*arel.orders)
        stmt.wheres = arel.constraints
      end

      bvs = arel.bind_values + bind_values
      @klass.connection.update stmt, 'SQL', bvs
    end

values() click to toggle source

    # File lib/active_record/relation.rb, line 623
    def values
      Hash[@values]
    end

where_values_hash(relation_table_name = table_name) click to toggle source

Returns a hash of where conditions.

    User.where(name: 'Oscar').where_values_hash
    # => {name: "Oscar"}

    # File lib/active_record/relation.rb, line 558
    def where_values_hash(relation_table_name = table_name)
      equalities = where_values.grep(Arel::Nodes::Equality).find_all { |node|
        node.left.relation.name == relation_table_name
      }

      binds = Hash[bind_values.find_all(&:first).map { |column, v| [column.name, v] }]

      Hash[equalities.map { |where|
        name = where.left.name
        [name, binds.fetch(name.to_s) {
          case where.right
          when Array then where.right.map(&:val)
          when Arel::Nodes::Casted
            where.right.val
          end
        }]
      }]
    end

### Private Instance Methods

build_preloader() click to toggle source

    # File lib/active_record/relation.rb, line 652
    def build_preloader
      ActiveRecord::Associations::Preloader.new
    end

exec_queries() click to toggle source

    # File lib/active_record/relation.rb, line 636
    def exec_queries
      @records = eager_loading? ? find_with_associations : @klass.find_by_sql(arel, arel.bind_values + bind_values)

      preload = preload_values
      preload +=  includes_values unless eager_loading?
      preloader = build_preloader
      preload.each do |associations|
        preloader.preload @records, associations
      end

      @records.each { |record| record.readonly! } if readonly_value

      @loaded = true
      @records
    end

references_eager_loaded_tables?() click to toggle source

    # File lib/active_record/relation.rb, line 656
    def references_eager_loaded_tables?
      joined_tables = arel.join_sources.map do |join|
        if join.is_a?(Arel::Nodes::StringJoin)
          tables_in_string(join.left)
        else
          [join.left.table_name, join.left.table_alias]
        end
      end

      joined_tables += [table.name, table.table_alias]

      # always convert table names to downcase as in Oracle quoted table names are in uppercase
      joined_tables = joined_tables.flatten.compact.map { |t| t.downcase }.uniq

      (references_values - joined_tables).any?
    end

tables_in_string(string) click to toggle source

    # File lib/active_record/relation.rb, line 673
    def tables_in_string(string)
      return [] if string.blank?
      # always convert table names to downcase as in Oracle quoted table names are in uppercase
      # ignore raw_sql_ that is used by Oracle adapter as alias for limit/offset subqueries
      string.scan(/([a-zA-Z_][.\w]+).?\./).flatten.map{ |s| s.downcase }.uniq - ['raw_sql_']
    end