# Django 2.2.9.dev20191202104323 文档

# django.db.models.constraints 源代码

    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)

    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

    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