Rails ActiveRecord return records where id exists in related table

ruby-on-rails activerecord active-record-query

Simplest but not the fastest:

Client.where(:id => Product.select(:client_id).map(&:client_id))

SQL subquery (more faster):

Client.where("EXISTS(SELECT 1 from products where clients.id = products.client_id)")

ruby-on-rails activerecord active-record-query

Here's another solution. It's a subquery like Valery's second solution, but without writing out the sql:

Client.where(Product.where(client_id: Client.arel_table[:id]).exists)

ruby-on-rails activerecord active-record-query

Here is the solution which uses Where Exists gem (disclosure: I'm its author):

Client.where_exists(:products)

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