06-CoreData增删改查

前言

• 数据库的操作无非就四个字：增删改查

如何查看CoreData操作数据库的过程？

• 添加SQL打印 在Edit schemes的Run中添加Arguments：-com.apple.CoreData.SQLDebug 1

1.1-CoreData增加数据

Person *p = [NSEntityDescription insertNewObjectForEntityForName:@"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];

通过log打印可以看出，CoreData插入一条数据只需要0.0001秒，这个效率还是非常高的