Realm可空属性,默认值,忽略属性,通知

文章类型： 学习笔记

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Realm文章链接:

1.iOS Realm简单使用(增删改查和排序)

2.Realm存储的类型和Realm数据库关系存储制

3.Realm可空属性,默认值,忽略属性,通知

4.Realm用户机制,数据库操作,数据库迁移

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Realm可空属性

@interface student : RLMObject

@property NSString *name;
@property int number;
@property float weight;
@property NSString *address;

@end

// This protocol enables typed collections. i.e.:
// RLMArray<student *><student>
RLM_ARRAY_TYPE(student)

//测试
student *stu  = [[student alloc] init];
stu.number = 22;

RLMRealm *realm = [RLMRealm defaultRealm];

[realm transactionWithBlock:^{
    [realm addObject:stu];
}];

结果

image_1bkh98c2cac31l801luojunku49.png-30.3kB

未约束可以有空值.

Realm非空值

@interface student : RLMObject

@property NSString *name;
@property int number;
@property float weight;
@property NSString *address;

@end

// This protocol enables typed collections. i.e.:
// RLMArray<student *><student>
RLM_ARRAY_TYPE(student)

//要强调非空值需要在.m中实现方法
//约束`address`字段不能为空
+ (NSArray<NSString *> *)requiredProperties {
    return @[@"address"];
}

默认值

@interface student : RLMObject

@property NSString *name;
@property int number;
@property float weight;
@property NSString *address;

@end

// This protocol enables typed collections. i.e.:
// RLMArray<student *><student>
RLM_ARRAY_TYPE(student)

//要强调非空值需要在.m中实现方法
//给`address`字段增加默认值
+ (NSDictionary *)defaultPropertyValues {
    return @{@"address":@"110"};
}

忽略属性(前文已经提到了)

//想忽略一个属性不让他存储
//1.加readonly
@property (readonly)NSString *name;
//2.实现中定方法
+ (NSArray<NSString *> *)ignoredProperties {
    return @[@"name"];
}

//一般开发中使用到时间
//存储时间,同时多存一个时间格式化后的字符串
@property NSTimeInterval time;
@property (readonly)NSString *timeFormat;
//重写time的set方法中转化为需要的时间样式赋值timeFormat,这样取得时候直接取格式化后的就行了
//这种时间格式化后的属性又被成为弱业务逻辑

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Realm通知

//Realm中存在通知,当用户修改数据库的时候会触发通知
//注:必须用强引用持有通知token
@property (nonatomic , strong)RLMNotificationToken *token;

//设置通知
RLMRealm *realm = [RLMRealm defaultRealm];

self.token = [realm addNotificationBlock:^(RLMNotification  _Nonnull notification, RLMRealm * _Nonnull realm) {
    NSLog(@"数据库发生改变了");
}];

//关闭通知
[self.token stop];


//结果集也可以时时监听,可以拿到改变的数值
//第一次RLMCollectionChange为改变的值,自己试试
@property (nonatomic , strong)RLMNotificationToken *token2;

RLMResults *result = [student allObjects];
self.token2 =[result addNotificationBlock:^(RLMResults * _Nullable results, RLMCollectionChange * _Nullable change, NSError * _Nullable error) {
    NSLog(@"结果集发生改变了");
}];