iOS 数据持久化方案-Realm的使用（下）

RLMResults<Student *> *students1 = [Student allObjects];
NSLog(@"第 1 次查询的结果：%@",students1);
RLMResults<Student *> *students2 = [Student objectsWhere:@"studentName = '小王'"];
NSLog(@"第 2 次查询的结果：%@",students2);

我们在这里采用先拿到相应条件下的数据，再根据分页（利用for循环）来展示数据
RLMResults<Student *> *students = [Student allObjects];
for (NSInteger i = 0; i < 2; i++) {
      Student *student = students[I];
      NSLog(@"结果是：%@",student);
}

// Query using a predicate string：使用谓词字符串进行查询
RLMResults<Student *> *students1 = [Student objectsWhere:@"studentName BEGINSWITH '小'"];
NSLog(@"students1=%@",students1);
// Query using an NSPredicate：使用NSPredicate查询
NSPredicate *pred = [NSPredicate predicateWithFormat:@"studentName BEGINSWITH %@",@"小"];
RLMResults<Student *> *student2 = [Student objectsWithPredicate:pred];
NSLog(@"students2=%@",student2);

@property NSData *imageData;

+ (NSArray *)ignoredProperties
{
   return @[@"image"];
}

@property Dog *dog;

Student *student = [[Student alloc]init];
student.studentId = 1;
student.studentName = @"小明";
Dog *dog = [[Dog alloc]init];
dog.dogId = 1;
dog.dogName = @"旺财";
student.dog = dog;
RLMRealm *realm = [RLMRealm defaultRealm];
[realm transactionWithBlock:^{
    [realm addObject:student];
}];

@property RLMArray<Dog *><Dog> *dogs;

Student *student = [[Student alloc]init];
student.studentId = 1;
student.studentName = @"小明";
Dog *dog1 = [[Dog alloc]init];
dog1.dogId = 1;
dog1.dogName = @"旺财";
Dog *dog2 = [[Dog alloc]init];
dog2.dogId = 2;
dog2.dogName = @"阿福";
[student.dogs addObject:dog1];
[student.dogs addObject:dog2];
RLMRealm *realm = [RLMRealm defaultRealm];
[realm transactionWithBlock:^{
    [realm addObject:student];
}];

@interface Dog : RLMObject
/** 狗的唯一ID */
@property int dogId;
/** 狗的名字 */
@property NSString *dogName;
@property (readonly) RLMLinkingObjects *owners;
@end
@implementation Dog
/** 设置主键 */
+(NSString *)primaryKey{
   return @"dogId";
}
+ (NSDictionary *)linkingObjectsProperties {
      return @{@"owners":[RLMPropertyDescriptor descriptorWithClass:NSClassFromString(@"Student") propertyName:@"dogs"]};
}
@end

RLMResults *results = [Student allObjects];
Student *student = results.firstObject;
Dog *dog = student.dogs.firstObject;
NSLog(@"owners=%@",dog.owners);

+(NSArray<NSString *> *)requiredProperties{
     return @[@"num"];
}

+ (NSDictionary *)defaultPropertyValues
{
   return @{@"catName":@"小花"};
}

/** 猫的年龄 */
@property(readonly) NSInteger catAge;

+ (NSArray *)ignoredProperties
{
    return @[@"catAge"];
}

@property (nonatomic, strong) RLMNotificationToken *token;

RLMRealm *realm = [RLMRealm defaultRealm];
// 创建通知
self.token = [realm addNotificationBlock:^(RLMNotification  _Nonnull notification, RLMRealm * _Nonnull realm) {
     NSLog(@"监听到修改通知");
}];

NotificationModel *model = [[NotificationModel alloc]init];
model.number = 1;
model.name = @"测试1";
RLMRealm *realm = [RLMRealm defaultRealm];
[realm transactionWithBlock:^{
      [realm addObject:model];
}];

[self.token invalidate];

@property (nonatomic, strong) RLMNotificationToken *token;

RLMResults *results = [NotificationModel allObjects];
self.token2 = [results addNotificationBlock:^(RLMResults * _Nullable results, RLMCollectionChange * _Nullable change, NSError * _Nullable error) {
     NSLog(@"%@--%@--%@", results, change, error); 
}];

[self.token invalidate];

NotificationModel *model = [[NotificationModel alloc]init];
model.number = 2;
model.name = @"测试2";
RLMRealm *realm = [RLMRealm defaultRealm];
[realm transactionWithBlock:^{
      [realm addObject:model];
}];
[realm transactionWithBlock:^{
     [realm deleteObject:model];
}];
NotificationModel *model2 = [[NotificationModel alloc]init];
model2.number = 3;
model2.name = @"测试3";
[realm transactionWithBlock:^{
     [realm addObject:model2];
}];

- (void)viewDidLoad {
   [super viewDidLoad];
   // Observe RLMResults Notifications
   __weak typeof(self) weakSelf = self;
   self.notificationToken = [[Person objectsWhere:@"age > 5"] addNotificationBlock:^(RLMResults<Person *> *results, RLMCollectionChange *changes, NSError *error) {
       if (error) {
            NSLog(@"Failed to open Realm on background worker: %@", error);
            return;
       }
       UITableView *tableView = weakSelf.tableView;
       // Initial run of the query will pass nil for the change information
       if (!changes) {
            [tableView reloadData];
            return;
       }
       // Query results have changed, so apply them to the UITableView
       [tableView beginUpdates];
       [tableView deleteRowsAtIndexPaths:[changes deletionsInSection:0] withRowAnimation:UITableViewRowAnimationAutomatic];
       [tableView insertRowsAtIndexPaths:[changes insertionsInSection:0] withRowAnimation:UITableViewRowAnimationAutomatic];
       [tableView reloadRowsAtIndexPaths:[changes modificationsInSection:0] withRowAnimation:UITableViewRowAnimationAutomatic];
       [tableView endUpdates];
    }];
}
- (void)dealloc {
    [self.notificationToken invalidate];
}

@interface RLMStepCounter : RLMObject
@property NSInteger steps;
@end
@implementation RLMStepCounter
@end
RLMStepCounter *counter = [[RLMStepCounter alloc] init];
counter.steps = 0;
RLMRealm *realm = [RLMRealm defaultRealm];
[realm beginWriteTransaction];
[realm addObject:counter];
[realm commitWriteTransaction];
__block RLMNotificationToken *token = [counter addNotificationBlock:^(BOOL deleted,NSArray<RLMPropertyChange *> *changes,NSError *error) {
     if (deleted) {
         NSLog(@"The object was deleted.");
     } else if (error) {
         NSLog(@"An error occurred: %@", error);
     } else {
         for (RLMPropertyChange *property in changes) {
              if ([property.name isEqualToString:@"steps"] && [property.value integerValue] > 1000) {
                    NSLog(@"Congratulations, you've exceeded 1000 steps.");
                    [token invalidate];
                    token = nil;
              }
         }
      }
}];

+(void)setDefaultRealmForUserDatabaseName:(NSString *)databaseName{
     RLMRealmConfiguration *config = [RLMRealmConfiguration defaultConfiguration];
     // 使用默认的目录，但是使用用户名来替换默认的文件名
     config.fileURL = [[[config.fileURL URLByDeletingLastPathComponent] URLByAppendingPathComponent: databaseName] URLByAppendingPathExtension:@"realm"];
     // 将这个配置应用到默认的 Realm 数据库当中
     [RLMRealmConfiguration setDefaultConfiguration:config]; 
}

//  数据库的配置
[RLMRealmDataBaseTools setDefaultRealmForUserName:@"王二"]; 
// 创建数据model
DataBaseModel *model = [DataBaseModel new];
model.number = 1;
// 获取对应数据库的 RLMRealm
RLMRealm *realm = [RLMRealm defaultRealm];
[realm transactionWithBlock:^{
    // 写入数据
    [realm addObject:model];
}];

+(void)setDefaultRealmReadOnly{
   RLMRealmConfiguration *config = [RLMRealmConfiguration defaultConfiguration];
   // 以只读模式打开文件，因为应用数据包并不可写
   config.readOnly = YES;
   [RLMRealmConfiguration setDefaultConfiguration:config];
}

+(void)deleteDatabaseName:(NSString *)databaseName{
     [self setDefaultRealmForUserDatabaseName:databaseName];
     NSFileManager *manager = [NSFileManager defaultManager];
     RLMRealmConfiguration *config = [RLMRealmConfiguration defaultConfiguration];
     NSArray<NSURL *> *realmFileURLs = @[
                             config.fileURL,
                             [config.fileURL URLByAppendingPathExtension:@"lock"],
                             [config.fileURL URLByAppendingPathExtension:@"management"],
                             ];
     for (NSURL *URL in realmFileURLs) {
          NSError *error = nil;
          [manager removeItemAtURL:URL error:&error];
          if (error) {
              // 处理错误
          }
     }  
}

+(void)databaseMigration:(int)newVersion{
   // 1. 获取默认配置
   RLMRealmConfiguration *config = [RLMRealmConfiguration defaultConfiguration];
   // 2. 叠加版本号(要比上一次的版本号高) 0
   config.schemaVersion = newVersion;
   // 3. 设置闭包，这个闭包将会在打开低于上面所设置版本号的 Realm 数据库的时候被自动调用
   [config setMigrationBlock:^(RLMMigration *migration, uint64_t oldSchemaVersion) {
         // 什么都不要做！Realm 会自行检测新增和需要移除的属性，然后自动更新硬盘上的数据库架构
         if (oldSchemaVersion < newVersion) {
         }
   }];
   // 4. 让配置生效（告诉 Realm 为默认的 Realm 数据库使用这个新的配置对象）
   [RLMRealmConfiguration setDefaultConfiguration:config];
   // 5. 我们已经告诉了 Realm 如何处理架构的变化，打开文件之后将会自动执行迁移,数据结构会发生变化
   [RLMRealm defaultRealm];    
}

if (oldSchemaVersion < newVersion) {
     NSLog(@"需要做迁移动作");
     //执行更名动作
     // [migration renamePropertyForClass:@"Migration" oldName:@"fullName" newName:@"fullName2"];
     // 无需做任何事情, 就可以完成, 数据结构, 以及数据的迁移
     [migration enumerateObjects:@"模型的名字" block:^(RLMObject * _Nullable oldObject, RLMObject * _Nullable newObject) {
         newObject[@"新的字段名字"] = [NSString stringWithFormat:@"%@", oldObject[@"旧的字段名字"]];
       }];
}

if (oldSchemaVersion < newVersion) {
    NSLog(@"需要做迁移动作");
    //执行更名动作
    [migration renamePropertyForClass:@"模型名字" oldName:@"旧字段名" newName:@"模型里新字段名"];
}

[migration enumerateObjects:Person.className
           block:^(RLMObject *oldObject, RLMObject *newObject) {
       // 只有当 Realm 数据库的架构版本为 0 的时候，才添加 “studentName” 属性
       if (oldSchemaVersion < 1) {
            newObject[@"studentName"] = @"";
       }
       // 只有当 Realm 数据库的架构版本为 0 或者 1 的时候，才添加“email”属性
       if (oldSchemaVersion < 2) {
             newObject[@"email"] = @"";
      }
      // 只有当 Realm 数据库的架构版本为 2 的时候，去掉“email”属性
       if (oldSchemaVersion < 3) {
             // 在后面执行 [RLMRealm defaultRealm];  后会自动更新模型结构
      }
}];