[PATCH] ActiveRecord::Calculations#count doesn't allow table names in column_name argument

Well, let's simplify the example:

User.count('orders.id', :joins => :orders, :group => 'users.id')

Schema: User has many orders.

The count() call without :group works:

User.count('orders.id', :joins => :orders)

I made up a pair of tests which prove the bug.

This would require changes in Arel because currently arel has following code.

def attribute(attribute)
  "#{quote_table_name(name_for(attribute.original_relation))}.#{quote_column_name(attribute.name)}" +
  (attribute.alias ? " AS #{quote(attribute.alias.to_s)}" : "")
end

That needs to be changed to something like this

def attribute(attribute, prefix = true)
  table_name = "#{quote_table_name(name_for(attribute.original_relation))}"
  column_name = "#{quote_column_name(attribute.name)}"
  qualified_name = prefix ? "#{table_name}.#{column_name}" : column_name
  qualified_name + (attribute.alias ? " AS #{quote(attribute.alias.to_s)}" : "")
end

Method execute_grouped_calculation in calculations.rb is executing

  Arel::Attribute.new(r, column_name).send(operation).as(aggregate_alias).to_sql

That needs to be changed to pass additional parameter to to_sql to tell it not to add prefix. Something like

  Arel::Attribute.new(r, column_name).send(operation).as(aggregate_alias).to_sql(:table_name => false)

Since simple count (not grouped) works, I looked into its implementation:

    def execute_simple_calculation(operation, column_name, distinct) #:nodoc:
      column = if @klass.column_names.include?(column_name.to_s)
        Arel::Attribute.new(@klass.unscoped, column_name)
      else
        Arel::SqlLiteral.new(column_name == :all ? "*" : column_name.to_s)
      end

      # Postgresql doesn't like ORDER BY when there are no GROUP BY
      relation = except(:order).select(operation == 'count' ? column.count(distinct) : column.send(operation))
      type_cast_calculated_value(@klass.connection.select_value(relation.to_sql), column_for(column_name), operation)
    end

Could this Arel::SqlLiteral thing help here? I tried to copy this if-statement to execute_grouped_calculation, but got very strange error messages somewhere from Arel.

Nice work Oleg. Your patch fixes the problem.

For some reason when I tried to apply your patch it said email is invalid.

Neeraj, it works for me (git am < file).

(from [a8a62f87f6777b1bad8f38cc4b0239b74a4f8a7a]) [#5441 [PATCH] ActiveRecord::Calculations#count doesn't allow table names in column_... state:resolved] refactoring code to determine aggregate column http://github.com/rails/rails/commit/a8a62f87f6777b1bad8f38cc4b0239...