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

Methods

Class Public methods

new(scope)

📝 Source code 
# File activerecord/lib/active_record/relation/query_methods.rb, line 18
      def initialize(scope)
        @scope = scope
      end
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Instance Public methods

missing(*args)

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
📝 Source code 
# File activerecord/lib/active_record/relation/query_methods.rb, line 71
      def missing(*args)
        args.each do |arg|
          reflection = @scope.klass._reflect_on_association(arg)
          opts = { reflection.table_name => { reflection.association_primary_key => nil } }
          @scope.left_outer_joins!(arg)
          @scope.where!(opts)
        end

        @scope
      end
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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')
📝 Source code 
# File activerecord/lib/active_record/relation/query_methods.rb, line 45
      def not(opts, *rest)
        where_clause = @scope.send(:build_where_clause, opts, rest)

        @scope.where_clause += where_clause.invert

        @scope
      end
🔎 See on GitHub