Can I join a table with no association? (rails/sql)
<p>I have these 3 classes:   </p>

<pre><code>class Factory &lt; ActiveRecord::Base
  has_many :machines
end

class Machine &lt; ActiveRecord::Base
  belongs_to :factory, inverse_of: :machines
  has_many :assembly_jobs, inverse_of: :machines
end

class AssemblyJob &lt; ActiveRecord::Base
  belongs_to :machines, inverse_of: :assembly_jobs
end
</code></pre>

<p>Schema</p>

<pre><code>Factories
- id

Machines
- factory_id

AssemblyJobs
- machine_id
- start_time
- error_time
- finish_time
</code></pre>

<p>I want to be write a scope in <code>factory.rb</code> to return any factories that have any machines with assembly jobs with error_time. Is this possible or do  I need to add a factory_id column to assembly job and create a belongs_to association?</p>