In a Rails app, I have a model, Machine, that contains the following named scope:

named_scope :needs_updates, lambda {
  { :select => self.column_names.collect{|c| "\"machines\".\"#{c}\""}.join(','),
    :group => self.column_names.collect{|c| "\"machines\".\"#{c}\""}.join(','),
    :joins => 'LEFT JOIN "machine_updates" ON "machine_updates"."machine_id" = "machines"."id"',
    :having => ['"machines"."manual_updates" = ? AND "machines"."in_use" = ? AND (MAX("machine_updates"."date") IS NULL OR MAX("machine_updates"."date") < ?)', true, true, UPDATE_THRESHOLD.days.ago]
  }
}

This named scope works fine in development mode. In production mode, however, it returns the 2 models as expected, but the models are empty or uninitialized; that is, actual objects are returned (not nil), but all the fields are nil. For example, when inspecting the return value of the named scope in the console, the following is returned:

[#<Machine >, #<Machine >]

But, as you can see, all the fields of the objects returned are set to nil.

The production and development environments are essentially the same. Both are using a SQLite database.

Any ideas what's going wrong?