How Do I Use Joins for Three Tables in Ruby on Rails?

Question

I am working on a Ruby on Rails application which already has logic for text searching using pg_search and two other fields on a model. The logic creates an 'array' of rows from the search result. I do not remember the actual name of this since technically this is not an array. It is an instance variable of selected rows. I want to add search criteria from two additional models. My database is PostgreSQL.

Here is a subset of all three model definitions:

MediaLibrary: name, media_creator_id, media_type_id (fields that are being used in current search; has many media_topics and has many media_targets)

MediaTopic: media_library_id, topic_id (want to search for topic_id; belongs to media_library; topic_id being searched is coming from a Topic model (id, name))

MediaTarget: media_library_id, target_id (want to search for target_id; belongs to media_library; target_id being searched is coming from a Target model (id, name))

I'm thinking that I should be able to do something like this if both topic and target are being searched along with the other three search criteria. I will also need to have topic_id and target_id in my results so I can display Topic.name and Target.name on my view.

@media_libraries = MediaLibrary.text_search(params[:query]).where("media_creator_id = ? AND media_type_id = ?", params[:media_creator_id].to_i, params[:media_type_id].to_i).joins(:media_topics.where("media_library_id = ? and topic_id = ?", id_from_media_library_row, params[:topic_id].to_i).joins(:media_targets.where("media_library_id = ? and target_id = ?", id_from_media_library_row, params[:target_id].to_i)

I have searched on postgresql.org and Stack Overflow but have not found anything joining three tables using Ruby on Rails that was answered by anyone.

Answer 1

You can pass a SQL join statement into #joins. I'm not sure what it'd be in your case but you can do something like:

@media_libraries = MediaLibrary.joins(%q(
  JOIN media_targets
    ON media_targets.media_library_id = media_libraries.id
  JOIN media_topics
    ON media_topics.media_library_id = media_libraries.id
)).text_search(params[:query])
  .where(
    media_libraries: {
      media_creator_id: params[:media_creator_id],
      media_type_id: params[:media_type_id]
    },
    media_topics: { id: params[:topic_id] },
  )