Question

Ok so I’m doing an inner join on an association in rails like so:

@visits = @customer.visits.joins(:messages).select("distinct(visits.id)")

And this is returning unique visit id’s however I want to loop through these visits, and access its associations (Each visit has a merchant_id attached to it as well). The problem with this inner join is that is is only returning the id so when I do something like this:

@visits.each do |v|
  merchant = v.merchant
end

I just end up with a nil class.

How can I select “visits” based on a unique visit.id but also return all the other columns in that row? Group by?

Answer 1

All you are selecting is the id, that’s correct. Since you want an object, you have two options. So what you really want is along the lines of:

Visit.where(:visit_id => @customers.visits.select("distinct(id)"))

This is equivalent to:

"SELECT * FROM VISITS WHERE VISITS.ID IN (SELECT DISTINCT(ID) FROM VISITS WHERE VISITS.CUSTOMER_ID IN ?)", <id_list>

I’m not sure where ‘messages’ factors in in your schema, but it’s basically just a join in the above query. Sometimes it;s helpful to figure out the SQL, and work backwards to ActiveRecord syntax if you’re having trouble.