Creates DROP DEFAULT if default value is a callable (Postgres) about aerich

[long2ice]

Yes, that's good, and you can run make style ci before commit, thanks for contribution!

[long2ice]

Can you show model difference before and after?

[madnesspie]

From migrations/old_models.py

# Before:
class ConfirmationCode(BaseAbstractModel, GetCredentialMixin):
    value = fields.CharField(
        max_length=8,
        default=lambda: ''.join(random.choice(string.digits) for i in range(8)),
        unique=True,
    )

    # Relations
    email = fields.ForeignKeyField(
        model_name="diff_models.Email",
        related_name="tokens",
        null=True,
    )
    phone = fields.ForeignKeyField(
        model_name="diff_models.Phone",
        related_name="tokens",
        null=True,
    )
    type = fields.ForeignKeyField(model_name="diff_models.ConfirmationCodeType")

    class Meta:
        table = "confirmation_code"

# After
class ConfirmationCode(BaseAbstractModel, GetCredentialMixin):
    value = fields.CharField(
        max_length=8,
        default=lambda: ''.join(random.choice(string.digits) for i in range(8)),
        unique=True,
    )
    fale_field_to_create_migration = fields.IntField(null=True)

    # Relations
    email = fields.ForeignKeyField(
        model_name="diff_models.Email",
        related_name="tokens",
        null=True,
    )
    phone = fields.ForeignKeyField(
        model_name="diff_models.Phone",
        related_name="tokens",
        null=True,
    )
    type = fields.ForeignKeyField(model_name="diff_models.ConfirmationCodeType")

    class Meta:
        table = "confirmation_code"

Generated migration:

{
  "upgrade": [
    "ALTER TABLE \"confirmation_code\" ALTER COLUMN \"value\" DROP DEFAULT",
    "ALTER TABLE \"confirmation_code\" ALTER COLUMN \"value\" TYPE VARCHAR(8)",
    "ALTER TABLE \"confirmation_code\" ADD \"fale_field_to_create_migration\" INT"
  ],
  "downgrade": [
    "ALTER TABLE \"confirmation_code\" ALTER COLUMN \"value\" DROP DEFAULT",
    "ALTER TABLE \"confirmation_code\" ALTER COLUMN \"value\" TYPE VARCHAR(8)",
    "ALTER TABLE \"confirmation_code\" DROP COLUMN \"fale_field_to_create_migration\""
  ]
}

[ALexALed]

Hi, thank you for the great tool! I have the same issue for the case where default=callable, I just wondering why the call for callable is omitted here?

aerich/aerich/ddl/__init__.py

Line 69 in 9879004

if callable(default) or isinstance(field_object, (UUIDField, TextField, JSONField)):

Can we add more sophisticated handling for callables as defaults?

[long2ice]

defaultgenerated in migrations is affected in database, obviously database can't support callable default.

[ALexALed]

@long2ice yes, you are right, sorry for the confusion, I said about change handling callable defaults in detect migrations, as an example this fix solve my issue:
Instead of:

aerich/aerich/migrate.py

Line 350 in a677d50

if new_field.default != old_field.default:

I use :

                        if new_field.default != old_field.default and not callable(
                            new_field.default
                        ):

What do you think about this change? I can make PR if you are ok with this

The main point: we shouldn't detect changes for callables in migrations