# Django 3.2.12 documentation

# Source code for django.db.models.constraints

    from enum import Enum

    from django.db.models.query_utils import Q
    from django.db.models.sql.query import Query

    __all__ = ['CheckConstraint', 'Deferrable', '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
            if not getattr(check, 'conditional', False):
                raise TypeError(
                    'CheckConstraint.check must be a Q instance or boolean '
                    'expression.'
                )
            super().__init__(name)

        def _get_check_sql(self, model, schema_editor):
            query = Query(model=model, alias_cols=False)
            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):
            if isinstance(other, CheckConstraint):
                return self.name == other.name and self.check == other.check
            return super().__eq__(other)

        def deconstruct(self):
            path, args, kwargs = super().deconstruct()
            kwargs['check'] = self.check
            return path, args, kwargs

    class Deferrable(Enum):
        DEFERRED = 'deferred'
        IMMEDIATE = 'immediate'

    class UniqueConstraint(BaseConstraint):
        def __init__(
            self,
            *,
            fields,
            name,
            condition=None,
            deferrable=None,
            include=None,
            opclasses=(),
        ):
            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.')
            if condition and deferrable:
                raise ValueError(
                    'UniqueConstraint with conditions cannot be deferred.'
                )
            if include and deferrable:
                raise ValueError(
                    'UniqueConstraint with include fields cannot be deferred.'
                )
            if opclasses and deferrable:
                raise ValueError(
                    'UniqueConstraint with opclasses cannot be deferred.'
                )
            if not isinstance(deferrable, (type(None), Deferrable)):
                raise ValueError(
                    'UniqueConstraint.deferrable must be a Deferrable instance.'
                )
            if not isinstance(include, (type(None), list, tuple)):
                raise ValueError('UniqueConstraint.include must be a list or tuple.')
            if not isinstance(opclasses, (list, tuple)):
                raise ValueError('UniqueConstraint.opclasses must be a list or tuple.')
            if opclasses and len(fields) != len(opclasses):
                raise ValueError(
                    'UniqueConstraint.fields and UniqueConstraint.opclasses must '
                    'have the same number of elements.'
                )
            self.fields = tuple(fields)
            self.condition = condition
            self.deferrable = deferrable
            self.include = tuple(include) if include else ()
            self.opclasses = opclasses
            super().__init__(name)

        def _get_condition_sql(self, model, schema_editor):
            if self.condition is None:
                return None
            query = Query(model=model, alias_cols=False)
            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]
            include = [model._meta.get_field(field_name).column for field_name in self.include]
            condition = self._get_condition_sql(model, schema_editor)
            return schema_editor._unique_sql(
                model, fields, self.name, condition=condition,
                deferrable=self.deferrable, include=include,
                opclasses=self.opclasses,
            )

        def create_sql(self, model, schema_editor):
            fields = [model._meta.get_field(field_name).column for field_name in self.fields]
            include = [model._meta.get_field(field_name).column for field_name in self.include]
            condition = self._get_condition_sql(model, schema_editor)
            return schema_editor._create_unique_sql(
                model, fields, self.name, condition=condition,
                deferrable=self.deferrable, include=include,
                opclasses=self.opclasses,
            )

        def remove_sql(self, model, schema_editor):
            condition = self._get_condition_sql(model, schema_editor)
            include = [model._meta.get_field(field_name).column for field_name in self.include]
            return schema_editor._delete_unique_sql(
                model, self.name, condition=condition, deferrable=self.deferrable,
                include=include, opclasses=self.opclasses,
            )

        def __repr__(self):
            return '<%s: fields=%r name=%r%s%s%s%s>' % (
                self.__class__.__name__, self.fields, self.name,
                '' if self.condition is None else ' condition=%s' % self.condition,
                '' if self.deferrable is None else ' deferrable=%s' % self.deferrable,
                '' if not self.include else ' include=%s' % repr(self.include),
                '' if not self.opclasses else ' opclasses=%s' % repr(self.opclasses),
            )

        def __eq__(self, other):
            if isinstance(other, UniqueConstraint):
                return (
                    self.name == other.name and
                    self.fields == other.fields and
                    self.condition == other.condition and
                    self.deferrable == other.deferrable and
                    self.include == other.include and
                    self.opclasses == other.opclasses
                )
            return super().__eq__(other)

        def deconstruct(self):
            path, args, kwargs = super().deconstruct()
            kwargs['fields'] = self.fields
            if self.condition:
                kwargs['condition'] = self.condition
            if self.deferrable:
                kwargs['deferrable'] = self.deferrable
            if self.include:
                kwargs['include'] = self.include
            if self.opclasses:
                kwargs['opclasses'] = self.opclasses
            return path, args, kwargs