Question

我开始使用Realm.io，我需要添加或更新To-Many关系RLMObject。想象一下，我有这样的RLMObjects：

#import <Realm/Realm.h>

@class Person;

// Dog model
@interface Dog : RLMObject
@property NSInteger id;
@property NSString *name;
@end
RLM_ARRAY_TYPE(Dog) // define RLMArray<Dog>

// Person model
@interface Person : RLMObject
@property NSString             *name;
@property NSDate               *birthdate;
@property RLMArray<Dog *><Dog> *dogs;
@end
RLM_ARRAY_TYPE(Person) // define RLMArray<Person>

Dogs RLMObject有一个主键（id），我正在阅读一个人和各种狗的json。我怎样才能添加这个人和他们的狗？

我将循环json人和狗阵列。例如，如果我使用上面的代码，关于Dogs对象的主键违规的领域警告：

RLMRealm *realm = [RLMRealm defaultRealm];
Dogs *dog = [[Dogs alloc] init];
[realm beginWriteTransaction];
   dog.id = 1;
   dog.name = @"Lupi";
   [realm addOrUpdateObject:dog];
   dog.id = 2;
   dog.name = @"rex";
   [realm addOrUpdateObject:dog]; 
[realm commitWriteTransaction];

Person *newPerson = [[Person alloc] init];
    [realm beginWriteTransaction];
        newPerson.id = 1;
        newPerson.name = @"John";
        [newPerson.dogs addObject:dog];
        [realm addOrUpdateObject:newPerson];
    [realm commitWriteTransaction];

Answer 1

如果您收到此错误'Primary key can't be changed after an object is inserted.'，原因是因为您尝试使用同一个对象。

dog.id = 1;
dog.name = @"Lupi";
[realm addOrUpdateObject:dog];

dog.id = 2; // This is not allowed. The primary key of the object that was saved once can not be changed.
dog.name = @"rex";
[realm addOrUpdateObject:dog];

Realm对象不是一个正确的值对象。当Realm对象保存一次时，它将被更改为连接到数据库的特殊对象。

所以dog.id = 2;意味着您将更改刚刚保存的对象。

每次要保存新对象时，都应创建新实例。如下所示：

Dog *dog1 = [[Dog alloc] init];
dog1.id = 1;
dog1.name = @"Lupi";
[realm addOrUpdateObject:dog1];

Dog *dog2 = [[Dog alloc] init];
dog2.id = 2;
dog2.name = @"rex";
[realm addOrUpdateObject:dog2];

[realm commitWriteTransaction];

从JSON

创建对象

如果您将从JSON创建新对象，如下所示：

{
  "person": {
    "id": 1,
    "name": "foo",
    "birthdate": "1980/10/28",
    "dogs": [
      {
        "id": 1,
        "name": "bar"
      },
      {
        "id": 2,
        "name": "baz"
      }
    ]
  }
}

你可以循环dog数组，在每个循环中创建新的Realm对象。

NSDictionary *json = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];

NSDictionary *person = json[@"person"];

[realm beginWriteTransaction];

Person *newPerson = [[Person alloc] init];
newPerson.id = [person[@"id"] integerValue];
newPerson.name = person[@"name"];

NSArray *dogs = person[@"dogs"];
for (NSDictionary *dog in dogs) {
    Dog *newDog = [[Dog alloc] init];
    newDog.id = [dog[@"id"] integerValue];
    newDog.name = dog[@"name"];
    [realm addOrUpdateObject:newDog];
}

[realm addOrUpdateObject:newPerson];

[realm commitWriteTransaction];

添加对象To-Many Relationships RLMObject

1 个答案:

从JSON