CoreData增删改查

1.1-CoreData增加数据

Person *p = [NSEntityDescriptioninsertNewObjectForEntityForName:@"Person"inManagedObjectContext:kManagedObjectContext.managedObjectContext];
p.age= @(13);   
p.name=@"张三";    
[kManagedObjectContext save];

1.2-CoreData查询数据

//1.创建一个查询请求 
 NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"Person"]; 
//2.创建查询谓词（查询条件）
 NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name == %@",@"张三"]; 
//3.给查询请求设置谓词
 request.predicate = predicate; 
//4.查询数据
 NSArray<Person*> *arr = [kManagedObjectContext.managedObjectContext executeFetchRequest:request error:nil]; 

 NSLog(@"%@====%@",arr.firstObject.name,arr.firstObject.age);

1.3-CoreData修改数据

//1.创建一个查询请求
 NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"Person"];
 //2.创建查询谓词（查询条件） 
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name == %@",@"张三"]; 
//3.给查询请求设置谓词 
request.predicate = predicate; 
//4.查询数据 
NSArray<Person*> *arr = [kManagedObjectContext.managedObjectContext executeFetchRequest:request error:nil];
 //5.改变数据 
arr.firstObject.name = @"李四";
arr.firstObject.age = @(18); 
//6.同步到数据库 
[kManagedObjectContext save];

1.4-CoreData删除数据

//1.创建一个查询请求
 NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"Person"];
 //2.创建查询谓词（查询条件）
 NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name == %@",@"张三"];
 //3.给查询请求设置谓词
 request.predicate = predicate; 
//4.查询数据 
NSArray<Person*> *arr = [kManagedObjectContext.managedObjectContext executeFetchRequest:request error:nil];
 //5.删除数据 
[kManagedObjectContext.managedObjectContext deleteObject:arr.firstObject]; 
//6.同步到数据库
 [kManagedObjectContext save];

1.5-CoreData清空数据库

• 清空数据库可以使用删除文件的方式
• 通过沙盒路径进入到沙盒可以看到数据库文件有三个，我们逐一删除便可
• 代码中的kFileName是一个宏 表示创建的路径

NSFileManager *fileManager = [NSFileManager defaultManager]; 
NSString *documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0]; 
//沙盒中三个文件 
NSString *filePath1 = [documentsPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.db",kFileName]]; 
NSString *filePath2 = [documentsPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.db-shm",kFileName]]; 
NSString *filePath3 = [documentsPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.db-wal",kFileName]];
 NSError *error;
 BOOL success = [fileManager removeItemAtPath:filePath1 error:&error]; 
[fileManager removeItemAtPath:filePath2 error:nil]; 
[fileManager removeItemAtPath:filePath3 error:nil];
 if (success) {
     NSLog(@"Remove fiel:%@ Success!",kFileName);
 } else { 
     NSLog(@"Could not delete file -:%@ ",[error localizedDescription]); 
}