How do I eager load multiple associations in same query with ActiveRecord?

Question

Given the following:

How do I in one query get all the model titles inside any one Project without using map or something similar AND without getting the N + 1 problem?

By using map, I have various solutions that work, but they all query the database more than once:

Project.joins(collectors: { gs_collector: :model }).find(92666).collectors.map{ |coll| coll.gs_collector.model.title }

You have misunderstood what joins is used for. joins is not actually used to eager load records and solve the common n+1 problem. It's used to add a INNER JOIN clause that can be used to filter out rows with no match in the join table or to add conditions based on the join table. No columns in the joined table will be selected. For eager loading you eager_load, preload or includes. bigbinary.com/blog/preload-vs-eager-load-vs-joins-vs-includes — max
– max, Commented Jun 1, 2024 at 8:56

Anton Bogdanov · Accepted Answer · 2024-05-29 19:58:46Z

1

You can do something like this

Model.joins(gs_collector: :collector).where(collectors: { project_id: 92666 }).pluck(:title)

answered May 29, 2024 at 19:58

Anton Bogdanov

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