WhereChain objects act as placeholder for queries in which where does not have any parameter. In this case, where can be chained to return a new relation.

Methods

Instance Public methods

associated(*associations)

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

You can define join type in the scope and associated will not use β€˜JOIN` by default.

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

 Post.left_joins(:comments).where.associated(:author)
 # SELECT "posts".* FROM "posts"
 # INNER JOIN "authors" ON "authors"."id" = "posts"."author_id"
 # LEFT OUTER JOIN "comments" ON "comments"."post_id" = "posts"."id"
#  WHERE "author"."id" IS NOT NULL
πŸ“ Source code 
# File activerecord/lib/active_record/relation/query_methods.rb, line 88
      def associated(*associations)
        associations.each do |association|
          reflection = scope_association_reflection(association)
          unless @scope.joins_values.include?(reflection.name) || @scope.left_outer_joins_values.include?(reflection.name)
            @scope.joins!(association)
          end

          if reflection.options[:class_name]
            self.not(association => { reflection.association_primary_key => nil })
          else
            self.not(reflection.table_name => { reflection.association_primary_key => nil })
          end
        end

        @scope
      end
πŸ”Ž See on GitHub

missing(*associations)

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
πŸ“ Source code 
# File activerecord/lib/active_record/relation/query_methods.rb, line 123
      def missing(*associations)
        associations.each do |association|
          reflection = scope_association_reflection(association)
          @scope.left_outer_joins!(association)
          if reflection.options[:class_name]
            @scope.where!(association => { reflection.association_primary_key => nil })
          else
            @scope.where!(reflection.table_name => { reflection.association_primary_key => nil })
          end
        end

        @scope
      end
πŸ”Ž See on GitHub

not(opts, *rest)

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')

If there is a non-nil condition on a nullable column in the hash condition, the records that have nil values on the nullable column won’t be returned.

User.create!(nullable_country: nil)
User.where.not(nullable_country: "UK")
# SELECT * FROM users WHERE NOT (nullable_country = 'UK')
# => []
πŸ“ Source code 
# File activerecord/lib/active_record/relation/query_methods.rb, line 49
      def not(opts, *rest)
        where_clause = @scope.send(:build_where_clause, opts, rest)

        @scope.where_clause += where_clause.invert

        @scope
      end
πŸ”Ž See on GitHub