from django.db.backends.ddl_references import Statement, Table from django.db.models import F, Q from django.db.models.constraints import BaseConstraint from django.db.models.sql import Query __all__ = ['ExclusionConstraint'] class ExclusionConstraint(BaseConstraint): template = 'CONSTRAINT %(name)s EXCLUDE USING %(index_type)s (%(expressions)s)%(where)s' def __init__(self, *, name, expressions, index_type=None, condition=None): if index_type and index_type.lower() not in {'gist', 'spgist'}: raise ValueError( 'Exclusion constraints only support GiST or SP-GiST indexes.' ) if not expressions: raise ValueError( 'At least one expression is required to define an exclusion ' 'constraint.' ) if not all( isinstance(expr, (list, tuple)) and len(expr) == 2 for expr in expressions ): raise ValueError('The expressions must be a list of 2-tuples.') if not isinstance(condition, (type(None), Q)): raise ValueError( 'ExclusionConstraint.condition must be a Q instance.' ) self.expressions = expressions self.index_type = index_type or 'GIST' self.condition = condition super().__init__(name=name) def _get_expression_sql(self, compiler, connection, query): expressions = [] for expression, operator in self.expressions: if isinstance(expression, str): expression = F(expression) if isinstance(expression, F): expression = expression.resolve_expression(query=query, simple_col=True) else: expression = expression.resolve_expression(query=query) sql, params = expression.as_sql(compiler, connection) expressions.append('%s WITH %s' % (sql % params, operator)) return expressions def _get_condition_sql(self, compiler, schema_editor, query): if self.condition is None: return None where = query.build_where(self.condition) 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): query = Query(model) compiler = query.get_compiler(connection=schema_editor.connection) expressions = self._get_expression_sql(compiler, schema_editor.connection, query) condition = self._get_condition_sql(compiler, schema_editor, query) return self.template % { 'name': schema_editor.quote_name(self.name), 'index_type': self.index_type, 'expressions': ', '.join(expressions), 'where': ' WHERE (%s)' % condition if condition else '', } def create_sql(self, model, schema_editor): return Statement( 'ALTER TABLE %(table)s ADD %(constraint)s', table=Table(model._meta.db_table, schema_editor.quote_name), constraint=self.constraint_sql(model, schema_editor), ) def remove_sql(self, model, schema_editor): return schema_editor._delete_constraint_sql( schema_editor.sql_delete_check, model, schema_editor.quote_name(self.name), ) def deconstruct(self): path, args, kwargs = super().deconstruct() kwargs['expressions'] = self.expressions if self.condition is not None: kwargs['condition'] = self.condition if self.index_type.lower() != 'gist': kwargs['index_type'] = self.index_type return path, args, kwargs def __eq__(self, other): return ( isinstance(other, self.__class__) and self.name == other.name and self.index_type == other.index_type and self.expressions == other.expressions and self.condition == other.condition ) def __repr__(self): return '<%s: index_type=%s, expressions=%s%s>' % ( self.__class__.__qualname__, self.index_type, self.expressions, '' if self.condition is None else ', condition=%s' % self.condition, )