Simple LEFT JOIN with default_scope

rubyonrails-talk
1

Hey everyone,

I’ve got two models: Admin and CallCenter. An Admin may belong to a CallCenter (the field is nullable). To keep history, Admins and CallCenters have a deleted field with, for both of them:

default_scope { where(deleted: false) }

``

Now, I want to implement Admin.all_detailed which will retrieve all non-deleted admins with their call center (LEFT JOIN). Simply doing a eager_load will make a join with the default_scope condition, thus, non-deleted admins which belong to a deleted call center will be shown not having one. The unscoped_associations gem didn’t solve this issue. Therefor, I did this:

def self.all_detailed return joins(“LEFT JOIN call_centers ON call_centers.id = admins.call_center”) end

``

But now, when accessing the call center method of each admin, it triggers a query:

SELECT call_centers.* FROM call_centers WHERE call_centers.id = @id LIMIT 1

``

I figured out the query doesn’t SELECT the call center’s fields:

SELECT admins.* FROM admins LEFT JOIN call_centers – …

``

So I added the SELECT fields:

def self.all_detailed return select(“admins., call_centers.”) .joins(“LEFT JOIN call_centers ON call_centers.id = admins.call_center”) end

``

But a query is still triggered for every access to the call_center method of Admin. It seems like Rails does not know how to link the SELECT with the Admin’s association, but I don’t see what else I can do.

Thanks for your help!

2

I suggest that the problem may actually lie with your db design. If I understand your question correctly you allow a non-deleted admin to belong to a call center that that has been deleted, which seems odd. Perhaps consider what is the status of a "deleted" call center that still has associated admins. Is this in fact truly deleted or should it not be considered deleted until it has no more admins?

As a side note I now avoid default_scope whenever practical, the use of it regularly turns up problems similar to yours.

Colin