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我可以在核心数据中获取关系数据吗?

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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 .

1 回答

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    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];
    

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