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from django.core import checks
from django.db.backends import BaseDatabaseValidation
class DatabaseValidation(BaseDatabaseValidation):
def check_field(self, field, **kwargs):
"""
MySQL has the following field length restriction:
No character (varchar) fields can have a length exceeding 255
characters if they have a unique index on them.
"""
from django.db import connection
errors = super(DatabaseValidation, self).check_field(field, **kwargs)
# Ignore any related fields.
if getattr(field, 'rel', None) is None:
field_type = field.db_type(connection)
# Ignore any non-concrete fields
if field_type is None:
return errors
if (field_type.startswith('varchar') # Look for CharFields...
and field.unique # ... that are unique
and (field.max_length is None or int(field.max_length) > 255)):
errors.append(
checks.Error(
('MySQL does not allow unique CharFields to have a max_length > 255.'),
hint=None,
obj=field,
id='mysql.E001',
)
)
return errors
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