Question

Here’s the erroneous code snippet.

transaction do    
    Person.having_email(some_email).find_each(:conditions => ["people.identifier != ? OR people.identifier IS NULL", identifier]) do |person|
        if person.identifier?
          raise "Person is associated with a different identifier"
        else
          duplicate_entry =  Person.find_by_identifier_and_company_id(identifier, person.company_id)
          person.update_attribute(:identifier, identifier) if duplicate_entry.nil?
        end
    end
end

having_email is a named_scope defined for the Person class.

The issue that I’m facing is that the expression that finds a possible duplicate entry always seems to be returning nil even when a valid record is present in the db. When I evaluate the same expression using the RubyMine debugger, it returns the correct object.

On further introspection, it seems that rails is not firing any query on the duplicate_entry evaluation statement(there is no such query in the logs). On replacing the find_each call with a normal find(:all, ...).each call, things seem to work fine(The duplicate entry retrieval query is present in the logs as well).

I haven’t been able to get my head around what might be causing this. Any ideas?

Answer 1

The problem is that find_each and find_in_batches work by setting up a
with_scope block. Therefore, if you need to do any other finds on that
same model, the scope will apply.

The root cause of this issue has been explained quite well along with a valid workaround in this blog post