# File activerecord/lib/active_record/relation/query_methods.rb, line 69
def associated(*associations)
  associations.each do |association|
    reflection = @scope.klass._reflect_on_association(association)
    @scope.joins!(association)
    self.not(reflection.table_name => { reflection.association_primary_key => nil })
  end

  @scope
end

Returns a new relation with joins and where clause to identify associated relations.

For example, posts that are associated to a related author:

Post.where.associated(:author)
# SELECT "posts".* FROM "posts"
# INNER JOIN "authors" ON "authors"."id" = "posts"."author_id"
# WHERE "authors"."id" IS NOT NULL

Additionally, multiple relations can be combined. This will return posts associated to both an author and any comments:

Post.where.associated(:author, :comments)
# SELECT "posts".* FROM "posts"
# INNER JOIN "authors" ON "authors"."id" = "posts"."author_id"
# INNER JOIN "comments" ON "comments"."post_id" = "posts"."id"
# WHERE "authors"."id" IS NOT NULL AND "comments"."id" IS NOT NULL

# File activerecord/lib/active_record/relation/query_methods.rb, line 97
def missing(*associations)
  associations.each do |association|
    reflection = @scope.klass._reflect_on_association(association)
    unless reflection
      raise ArgumentError.new("An association named `:#{association}` does not exist on the model `#{@scope.name}`.")
    end
    @scope.left_outer_joins!(association)
    @scope.where!(reflection.table_name => { reflection.association_primary_key => nil })
  end

  @scope
end

Returns a new relation with left outer joins and where clause to identify missing relations.

For example, posts that are missing a related author:

Post.where.missing(:author)
# SELECT "posts".* FROM "posts"
# LEFT OUTER JOIN "authors" ON "authors"."id" = "posts"."author_id"
# WHERE "authors"."id" IS NULL

Additionally, multiple relations can be combined. This will return posts that are missing both an author and any comments:

Post.where.missing(:author, :comments)
# SELECT "posts".* FROM "posts"
# LEFT OUTER JOIN "authors" ON "authors"."id" = "posts"."author_id"
# LEFT OUTER JOIN "comments" ON "comments"."post_id" = "posts"."id"
# WHERE "authors"."id" IS NULL AND "comments"."id" IS NULL

# File activerecord/lib/active_record/relation/query_methods.rb, line 43
def not(opts, *rest)
  where_clause = @scope.send(:build_where_clause, opts, rest)

  @scope.where_clause += where_clause.invert

  @scope
end

Returns a new relation expressing WHERE + NOT condition according to the conditions in the arguments.

not accepts conditions as a string, array, or hash. See QueryMethods#where for more details on each format.

User.where.not("name = 'Jon'")
# SELECT * FROM users WHERE NOT (name = 'Jon')

User.where.not(["name = ?", "Jon"])
# SELECT * FROM users WHERE NOT (name = 'Jon')

User.where.not(name: "Jon")
# SELECT * FROM users WHERE name != 'Jon'

User.where.not(name: nil)
# SELECT * FROM users WHERE name IS NOT NULL

User.where.not(name: %w(Ko1 Nobu))
# SELECT * FROM users WHERE name NOT IN ('Ko1', 'Nobu')

User.where.not(name: "Jon", role: "admin")
# SELECT * FROM users WHERE NOT (name == 'Jon' AND role == 'admin')