django Model.objects.raw返回SUM字段为Decimal

Question

I have a django model defined as follows:

class Foo(models.Model):
    bar = models.IntegerField(null=True)
    baz = models.ForeignKey(Baz)

class Baz(models.Model):
    bat = models.IntegerField(null=True)

I perform a Foo.objects.raw() aggregation query on it as follows:

sql = """
      SELECT -1 AS id,
      SUM( foo.bar ) AS bar
      FROM myapp_foo
      LEFT JOIN myapp_baz ON foo.baz_id = baz.id
      GROUP BY myapp_baz.id;
      """

aggregate_foo = Foo.objects.raw(sql)

Which all works fine, but when I access aggregate_foo.bar it returns a Decimal instead of an int! Of course I could cast bar into an int after the fact but I'd rather do this the right way.

Has anybody else run into this undocumented "feature" of the django raw() function? Is there a proper way to write the sql so that it will return the SUM( ) field as an int? I understand that I don't NEED to perform a raw query in the example above, but let's just assume for the sake of this question that I can't use Foo.objects.aggregate( )

Dunno if it's crucial to this question but my datastore is MySQL 5.5

Answer 1

It is a feature of MySQL, and not django. Hence not documented in django.

From the documentation

For numeric arguments, the variance and standard deviation functions return a DOUBLE value. The SUM() and AVG() functions return a DECIMAL value for exact-value arguments (integer or DECIMAL), and a DOUBLE value for approximate-value arguments (FLOAT or DOUBLE). (Before MySQL 5.0.3, SUM() and AVG() return DOUBLE for all numeric arguments.)

Hence the result.