SchemaEditor + DatabaseConnection

[Christopher D'Cunha]

Hi All,

I'm working on https://code.djangoproject.com/ticket/56 for the EuroPython sprint. There was a PR for it (https://github.com/django/django/pull/1156) but it was rejected by Tim Graham because the code should apparently be in the SchemaEditor instead of the DatabaseCreation class. 

As I trace through though I see that the SchemaEditor uses the DatabaseCreation for some stuff. For example, in order to get the column type for a field:

# /django/db/backends/schema.py

class BaseDatabaseSchemaEditor(object):
    ...

    def create_model(self, model):
         ...

        for field in model._meta.local_fields:
            ...

            # Check constraints can go on the column SQL here

            db_params = field.db_parameters(connection=self.connection)


# /django/db/models/fields/__init__.py

class Field(RegisterLookupMixin):

    """Base class for all field types"""

    ...

    def db_parameters(self, connection):
        ...
        type_string = self.db_type(connection)
        ...

    def db_type(self, connection):

        data = DictWrapper(self.__dict__, connection.ops.quote_name, "qn_")

        try:

            return connection.creation.data_types[self.get_internal_type()] % data

        except KeyError:

            return None

Is it possible/worth it for me to work on #56 before all the "migrate" stuff is done?

+AndrewGodwin, I'm told that you're the best person to ask :D.

Thanks,

Chris

[Tim Graham]

FWIW, I may have closed that PR prematurely. I didn't realize SchemaEditor still relied on DatabaseCreation and I'm not sure what the final combination of the two will ultimately look like.

[Andrew Godwin]

At the moment you'll need to make sure both Creation and SchemaEditor do the right thing for stuff like that. We bumped "deprecate DatabaseCreation" back to 2.0 for a final removal as it was so complex and so much stuff relies on it (including SchemaEditor in places where I didn't want to duplicate code; we'll move that code over eventually)

Andrew

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