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| require 'rom/memory' | |
| class BlenderRelation < ROM::Relation[:memory] | |
| repository :memory | |
| register_as :blender | |
| forward :join | |
| end | |
| class PostWithTagsMapper < ROM::Mapper | |
| relation :blender | |
| register_as :with_tags | |
| model PostWithTag | |
| end | |
| class TagRelation < ROM::Relation[:sql] | |
| dataset :tags | |
| one_to_many :taggings, key: :tag_id | |
| def for_posts | |
| association_join(:taggings) | |
| .where(taggings__taggable_type: 'Post', | |
| taggings__taggable_id: Array(announcements).map{|a| a[:id] }) | |
| .select(:name, :taggable_id) | |
| end | |
| end | |
| class TagListMapper < ROM::Mapper | |
| attribute :id, from: :taggable_id | |
| group :tags do | |
| attribute :name | |
| end | |
| end | |
| class TagBlender | |
| attr_reader :rom | |
| def initialize(rom = ROM.env) | |
| @rom = rom | |
| end | |
| def with_tags(posts, tag_list) | |
| rom.relation(:blender).join(posts.to_a, (posts >> tag_list).to_a) | |
| end | |
| end | |
| blender = TagBlender.new(ROM.env) | |
| posts = ROM.env.relation(:posts).page(2) | |
| tags = ROM.env.relation(:tags).as(:tag_list) | |
| blender.with_tags(posts, tags).as(:with_tag) |
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