Numeric validator precision/scale validation fails for certain floats on MRI 1.9.3

[ashervb]

In validators/numeric_validator.rb on line 38

      def value_as_string(value)
        case value
          # Avoid Scientific Notation in Float to_s
          when Float      then value.to_d.to_s('F')
          when BigDecimal then value.to_s('F')
          else value.to_s
        end
      end

Given: f=-75.6942185

We call, f.to_d.to_s('F')

On all rubies except 1.9.3 we get:

"-75.6942185"

On MRI 1.9.3 we get:

"-75.69421850000001"

When then causes the validator to report an invalid precision/scale

[krzysztofjablonski]

The same problem with number: 842.31

1.9.3p0 :001 > 842.31.to_d.to_s
=> "842.3099999999999" 

This means that we can have random validation errors ("Value is not a number") during save model.

In ruby 1.9.3 method to_d in Foat class changed:

class Float < Numeric
  def to_d(precision=nil)
    BigDecimal(self, precision || Float::DIG+1)
  end
end

In ruby 1.9.2 it was:

class Float < Numeric
  def to_d
    BigDecimal(self.to_s)
  end
end

This is why it works in 1.9.2 and doesn't work in 1.9.3.

1.9.3p0 :008 > BigDecimal(842.31, Float::DIG+1).to_s
 => "842.3099999999999" 
1.9.3p0 :009 > BigDecimal(842.31.to_s).to_s
 => "842.31" 

To fix it in your app you can override to_d method like this:

class Float < Numeric
  def to_d(precision=nil)
   if precision
     BigDecimal(self, precision)
   else
     BigDecimal(self.to_s)
   end
  end
end

but this monkeypatch is not the best idea and it should be fixed somehow in DM.

[krzysztofjablonski]

This is safer fix (for DM-core ~> 1.1.0):

# Ruby 1.9.3 hack

module DataMapper
  class Property
    class Decimal193 < Decimal
      def typecast_to_primitive(value)
        if value.kind_of?(::Integer)
          value.to_s.to_d
        elsif value.kind_of?(::Float)
          BigDecimal(value.to_s)
        else
          typecast_to_numeric(value, :to_d)
        end
      end
    end
  end
end

and then use Decimal193 instead of Decimal in your models.