Java通用lambda调用(Java generic lambda call)

 我也是CoreData的新手，但在我看来，谓词是错误的。 根据日志记录，您将personToDepartment.departmentName与部门对象进行比较。 谓词应该如下所示： NSPredicate *predicate = [NSPredicate predicateWithFormat:@"personToDepartment.departmentName = %@", selectedDepartment.departmentName]; 
 
 但还有更好的方法。 selectedDepartment.departmentToPerson将返回一个NSSet，其中包含属于该部门的所有人员（如果先前已设置了关系）。 但是警告，如果你要尝试NSLog(@"%@", selectedDepartment.departmentToPerson)你可能会得到“ 关系错误 ”，因为在你通过NSSet寻址特定对象或通过它枚举之前，CoreData不会进行获取。 但是例如NSLog(@"%d", selectedDepartment.departmentToPerson.count)将强制CoreData进行获取，你将看到部门中的人数。 
 
 更新：NSSet为空可能是因为您在创建人物对象时没有设置关系。 将自动设置从部门到人员的反向To-Many关系。 
 
- (id)insertNewPerson:(NSDictionary *)personInfo inDepartment:(Department*)departmentObject 
{
    Person *personObject = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:context];
    personObject.name = personInfo.name;
    personObject.departmentName = departmentObject.name;
    ...
    personObject.personToDepartment = departmentObject;   //this is RELATIONSHIP, if set, then you can access all persons from specific department by doing: departmentObject.departmentToPerson
}

I'm also kind of newbie to CoreData, but it seems to me that predicate is wrong. According to Log record you're about to comparing personToDepartment.departmentName to a department Object. Predicate should look like: NSPredicate *predicate = [NSPredicate predicateWithFormat:@"personToDepartment.departmentName = %@", selectedDepartment.departmentName];
 
But there is a better way. selectedDepartment.departmentToPerson will return an NSSet with all persons belonging to this department (if relationship was set previously). But warning, if you'll try to NSLog(@"%@", selectedDepartment.departmentToPerson) probably you'll get "relationship fault", because CoreData will not do fetch until you address specific object in NSSet or enumerate through it. But for example NSLog(@"%d", selectedDepartment.departmentToPerson.count) will force CoreData to make fetch and you'll see number of persons in department.
 
UPDATE: NSSet is empty probably because you are not setting relationship, when creating person's object. Inverse To-Many relationship from department to persons will be set automatically.
 
- (id)insertNewPerson:(NSDictionary *)personInfo inDepartment:(Department*)departmentObject 
{
    Person *personObject = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:context];
    personObject.name = personInfo.name;
    personObject.departmentName = departmentObject.name;
    ...
    personObject.personToDepartment = departmentObject;   //this is RELATIONSHIP, if set, then you can access all persons from specific department by doing: departmentObject.departmentToPerson
}