It works for me in edge for postgres.

ree-1.8.7-2010.02 > Post.calculate(:average, 'rating')
 => #<BigDecimal:102740628,'0.125E2',18(27)> 
ree-1.8.7-2010.02 >

It works for me in edge for postgres.

ree-1.8.7-2010.02 > Post.calculate(:average, 'rating')
 => #<BigDecimal:102740628,'0.125E2',18(27)> 
ree-1.8.7-2010.02 >

Maybe a MySQL driver-related issue? Or could this have been fixed in edge, shall I try?

Think this bug is related with the type cast of the calculated value. the activerecord tries to cast the value based on the type of the column.

If the rating column is of type integer it should calculate integer/integer = integer. If raging is of type float, it calculates float/integer = float.

What is the type of your rating column ?

Did a quick test with a fresh rails install and sqlite3, and the calculated value is different for columns of type integer and float.

My :ratings are integer. Maybe this is the problem because the avg() of integer values still can be float - the avg() of 1 and 2 is not 1 but 1.5

In ticket 6158 ( #6158 #count on decimal column returns BigDecimal ), performing a COUNT() operation on a decimal column is returning a decimal, event though a count should always be a whole integer. I've already added a unit test and patch for that particular patch. I suppose this is the inverse of that issue.

There's a method in /lib/active_record/relation/calculations.rb that coerces the type returned to be the same as the column type.

Think that the bug is related with type_cast method in the schema_definitions.rb

If you create a second field rating2 of type float, and test Post.average(:rating) vs Post.average(:rating2), you will notice that the value class in on both Float, but the class of type is integer and float respectively.

From the comment in the code i think that value is supposed to be String, but as you can test, it can be also a float. A small fix can be: "return value if !value.is_a?(String)" in the beginning of the type_cast method.

Casts value (which is a String) to an appropriate instance.

def type_cast(value)
return nil if value.nil? puts "Class: #{type.class}" puts "Type: #{type}" puts "Value class: #{value.class}" puts "Value: #{value}" case type

end end

     # Casts value (which is a String) to an appropriate instance.
      def type_cast(value)
        return nil if value.nil?
        puts "Class: #{type.class}"
        puts "Type: #{type}"
        puts "Value class: #{value.class}"
        puts "Value: #{value}"
        case type
          when :string    then value
          when :text      then value
          when :integer   then value.to_i rescue value ? 1 : 0
          when :float     then value.to_f
          when :decimal   then self.class.value_to_decimal(value)
          when :datetime  then self.class.string_to_time(value)
          when :timestamp then self.class.string_to_time(value)
          when :time      then self.class.string_to_dummy_time(value)
          when :date      then self.class.string_to_date(value)
          when :binary    then self.class.binary_to_string(value)
          when :boolean   then self.class.value_to_boolean(value)
          else value
        end
      end

This bug comes form commit - we should always cast the value based on the column October 11, 2010 when calculations type casts was changed.

in module Calculations method:

def type_cast_calculated_value(value, column, operation = nil)
  if value.is_a?(String) || value.nil?
    case operation
      when 'count' then value.to_i
      when 'sum' then type_cast_using_column(value || '0', column)
      when 'average' then value.try(:to_d)
      else type_cast_using_column(value, column)
    end
  else
    value
  end
end

was changed to:

def type_cast_calculated_value(value, column, operation = nil)

  if value.is_a?(String) || value.nil?
    case operation
      when 'count' then value.to_i
      when 'sum' then type_cast_using_column(value || '0', column)
      when 'average' then value.try(:to_d)
      else type_cast_using_column(value, column)
    end
  else
    type_cast_using_column(value, column)
  end
end

new method is not working any more as described in documentation for Calculate method (AVG should return Float)

I created pull request with fix for this issue

https://github.com/rails/rails/pull/160