method

missing

v6.1.7.7 - Show latest stable - 0 notes - Class: WhereChain

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What's this?

missing(*args) public

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

Show source

# 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

missing

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