manage.py inspect db is not using the new DecimalField

[James <james_027@…>]

Hi,

I've use the manage.py inspectdb utility. It's very nice but it is still using the model.FloatField rather than model.DecimalField.

Thanks
james

[Philippe Raoult]

This model:

class DecimalTest(models.Model):
    test = models.DecimalField(max_digits=10, decimal_places=3)

will be introspected as:

class TimesheetDecimaltest(models.Model):
    id = models.IntegerField(primary_key=True)
    test = models.TextField() # This field type is a guess.
    class Meta:
        db_table = u'timesheet_decimaltest'

using activepython 2.5.1 under windows xp, with sqlite3 backend.

Could you please add more details about your config, especially the backend you used?

[jmelesky]

I've verified the problem on OSX, sqlite3, Py25. And i've verified that the problem is *not* present using MySQL 5ish, debian, Py24.

From the code, i'm guessing this is a problem with the sqlite introspection only. The Postgres and Oracle code both seem to already take DecimalFields into account (though i haven't tested this). I've attached a patch.

[Philippe Raoult]

Can you reupload the patch ? it got lost by trac it seems (known issue over the weekend).

[Claude Paroz]

Updated/completed patch with tests

[Claude Paroz]

I added a patch which adds guessed max_digits and decimal_places for SQLite (with a notice) because decimal fields in SQLite are simply mapped as real (float) type. This way, the output of inspectdb is valid.

The problem with the current patch is that it doesn't pass with MySQL. Strangely, my version of mysqldb (1.2.2-10+b1) is always returning the value + 2 in cursor.description[4] (precision). Is this a known mysqldb bug?

[Claude Paroz]

After some more research, I think that this might be due to historically reasons. MySQL used to store decimal fields as strings, and the length returned was also counting a place for the dot and the sign, hence the + 2.
I'm attaching a patch that fixes this peculiarity in MySQL introspection file.

[Claude Paroz]

Same patch with mysql introspection fix

[Claude Paroz <claude@…>]

In 51028f50b624efae273dcbe828ec80c1846c74dc:

Fixed getting max_digits for MySQL decimal fields

Refs #5014.

[Claude Paroz <claude@…>]

In dcf563071fad7fe286c6921c949639fc99f51351:

Fixed #5014 -- Guessed max_digits and decimal_places for SQLite

Decimal is treated as float on SQLite, hence inspectdb can only
guess max_digits and decimal_places arguments.