from django.db.models.query_utils import Q
from django.db.models.sql.query import Query
__all__ = ['CheckConstraint', 'UniqueConstraint']
class BaseConstraint:
def __init__(self, name):
self.name = name
def constraint_sql(self, model, schema_editor):
raise NotImplementedError('This method must be implemented by a subclass.')
def create_sql(self, model, schema_editor):
raise NotImplementedError('This method must be implemented by a subclass.')
def remove_sql(self, model, schema_editor):
raise NotImplementedError('This method must be implemented by a subclass.')
def deconstruct(self):
path = '%s.%s' % (self.__class__.__module__, self.__class__.__name__)
path = path.replace('django.db.models.constraints', 'django.db.models')
return (path, (), {'name': self.name})
def clone(self):
_, args, kwargs = self.deconstruct()
return self.__class__(*args, **kwargs)
[文档]class CheckConstraint(BaseConstraint):
def __init__(self, *, check, name):
self.check = check
super().__init__(name)
def _get_check_sql(self, model, schema_editor):
query = Query(model=model)
where = query.build_where(self.check)
compiler = query.get_compiler(connection=schema_editor.connection)
sql, params = where.as_sql(compiler, schema_editor.connection)
return sql % tuple(schema_editor.quote_value(p) for p in params)
def constraint_sql(self, model, schema_editor):
check = self._get_check_sql(model, schema_editor)
return schema_editor._check_sql(self.name, check)
def create_sql(self, model, schema_editor):
check = self._get_check_sql(model, schema_editor)
return schema_editor._create_check_sql(model, self.name, check)
def remove_sql(self, model, schema_editor):
return schema_editor._delete_check_sql(model, self.name)
def __repr__(self):
return "<%s: check='%s' name=%r>" % (self.__class__.__name__, self.check, self.name)
def __eq__(self, other):
return (
isinstance(other, CheckConstraint) and
self.name == other.name and
self.check == other.check
)
def deconstruct(self):
path, args, kwargs = super().deconstruct()
kwargs['check'] = self.check
return path, args, kwargs
[文档]class UniqueConstraint(BaseConstraint):
def __init__(self, *, fields, name, condition=None):
if not fields:
raise ValueError('At least one field is required to define a unique constraint.')
if not isinstance(condition, (type(None), Q)):
raise ValueError('UniqueConstraint.condition must be a Q instance.')
self.fields = tuple(fields)
self.condition = condition
super().__init__(name)
def _get_condition_sql(self, model, schema_editor):
if self.condition is None:
return None
query = Query(model=model)
where = query.build_where(self.condition)
compiler = query.get_compiler(connection=schema_editor.connection)
sql, params = where.as_sql(compiler, schema_editor.connection)
return sql % tuple(schema_editor.quote_value(p) for p in params)
def constraint_sql(self, model, schema_editor):
fields = [model._meta.get_field(field_name).column for field_name in self.fields]
condition = self._get_condition_sql(model, schema_editor)
return schema_editor._unique_sql(model, fields, self.name, condition=condition)
def create_sql(self, model, schema_editor):
fields = [model._meta.get_field(field_name).column for field_name in self.fields]
condition = self._get_condition_sql(model, schema_editor)
return schema_editor._create_unique_sql(model, fields, self.name, condition=condition)
def remove_sql(self, model, schema_editor):
condition = self._get_condition_sql(model, schema_editor)
return schema_editor._delete_unique_sql(model, self.name, condition=condition)
def __repr__(self):
return '<%s: fields=%r name=%r%s>' % (
self.__class__.__name__, self.fields, self.name,
'' if self.condition is None else ' condition=%s' % self.condition,
)
def __eq__(self, other):
return (
isinstance(other, UniqueConstraint) and
self.name == other.name and
self.fields == other.fields and
self.condition == other.condition
)
def deconstruct(self):
path, args, kwargs = super().deconstruct()
kwargs['fields'] = self.fields
if self.condition:
kwargs['condition'] = self.condition
return path, args, kwargs
