Pluck associated model's attribute in Rails query

Question

In my rails app, collections have many projects, and projects have many steps.

I\'d like to grab all the ids of steps

Answer 1

Try this:

Step.joins(:project).where(projects: { collection_id: @collection.id }).pluck(:'steps.id')

Note the use of project for the joins, and then projects for the where clause. The first corresponds to the belongs_to relationship, and the latter is the name of the db table.

edit: in the case of a many-to-many relationship between projects and collections, and assuming a project belongs_to a project_collection (and then has_many :collections, through :project_collection)

Step.joins(:project => :project_collection)
    .where(project_collections: { collection_id: @collection.id })
    .pluck(:'steps.id')