我可以在核心数据中获取关系数据吗?这种关系是一对多的 .
例如:我有2个实体(部门和员工) . 该部门有多对员工关系,员工有一对一的部门关系 . 我想得到部门实体的员工 . 我可以使用fetch函数来获取数据吗?
提前致谢 .
您可以使用relationship属性获取部门的员工集:
Department *theDepartment = ...; // your department NSSet *employeesInDepartment = theDepartment.employees; // set of Employee objects
或者,如果您需要一个数组:
NSArray *employeesInDepartment = [theDepartment.employees allObjects];
或者,您可以使用以下提取请求:
Department *theDepartment = ...; // your department NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Employee"]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"department = %@", theDepartment]; [request setPredicate:predicate]; NSError *error; NSArray *employees = [yourManagedObjectContext executeFetchRequest:request error:&error];
1 回答
您可以使用relationship属性获取部门的员工集:
或者,如果您需要一个数组:
或者,您可以使用以下提取请求: