# 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

Compares two relations for equality.

# File activerecord/lib/active_record/relation.rb, line 227
def any?
  return super if block_given?
  !empty?
end

Returns true if there are any records.

# File activerecord/lib/active_record/relation.rb, line 503
def blank?
  records.blank?
end

Returns true if relation is blank.

# 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

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.

# 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

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, ...>

# 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

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!.

# 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

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

# File activerecord/lib/active_record/relation.rb, line 364
def destroy_all
  records.each(&:destroy).tap { reset }
end

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

# 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

Returns true if relation needs eager loading.

# File activerecord/lib/active_record/relation.rb, line 215
def empty?
  return @records.empty? if loaded?
  !exists?
end

Returns true if there are no records.

# File activerecord/lib/active_record/relation.rb, line 205
def encode_with(coder)
  coder.represent_seq(nil, records)
end

Serializes the relation objects Array.

# File activerecord/lib/active_record/relation.rb, line 189
def explain
  exec_explain(collecting_queries_for_explain { exec_queries })
end

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 activerecord/lib/active_record/relation.rb, line 163
def find_or_create_by(attributes, &block)
  find_by(attributes) || create(attributes, &block)
end

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.transaction(requires_new: true) do
    CreditAccount.find_or_create_by(user_id: user.id)
  end
rescue ActiveRecord::RecordNotUnique
  retry
end

# File activerecord/lib/active_record/relation.rb, line 170
def find_or_create_by!(attributes, &block)
  find_by(attributes) || create!(attributes, &block)
end

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

# File activerecord/lib/active_record/relation.rb, line 176
def find_or_initialize_by(attributes, &block)
  find_by(attributes) || new(attributes, &block)
end

Like find_or_create_by, but calls new instead of create.

# File activerecord/lib/active_record/relation.rb, line 482
def joined_includes_values
  includes_values & joins_values
end

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 activerecord/lib/active_record/relation.rb, line 421
def load(&block)
  exec_queries(&block) unless loaded?

  self
end

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 activerecord/lib/active_record/relation.rb, line 239
def many?
  return super if block_given?
  limit_value ? records.many? : size > 1
end

Returns true if there is more than one record.

# File activerecord/lib/active_record/relation.rb, line 56
def new(attributes = nil, &block)
  scoping { klass.new(values_for_create(attributes), &block) }
end

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

# File activerecord/lib/active_record/relation.rb, line 221
def none?
  return super if block_given?
  empty?
end

Returns true if there are no records.

# File activerecord/lib/active_record/relation.rb, line 233
def one?
  return super if block_given?
  limit_value ? records.one? : size == 1
end

Returns true if there is exactly one record.

# File activerecord/lib/active_record/relation.rb, line 428
def reload
  reset
  load
end

Forces reloading of relation.

# 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

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 activerecord/lib/active_record/relation.rb, line 210
def size
  loaded? ? @records.length : count(:all)
end

Returns size of the records.

# File activerecord/lib/active_record/relation.rb, line 194
def to_ary
  records.dup
end

Converts relation objects to Array.

# 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

Returns sql statement for the relation.

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

# 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

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')

# 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

Returns a hash of where conditions.

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