• 创建一个模型文件（相当于创建了一个数据库)

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• 创建一个实体就相当于创建了一张表（在attribut添加属性）

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• 创建一个实体类相当于创建了一个模型类

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• 获取上下文

 -(void)setupContext{
    
    // 1.上下文 关联Company.xcdatamodeld 模型文件
    NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init];
    
    // 关联模型文件
    
    // 创建一个模型对象
    // 传一个nil 会把 bundle下的所有模型文件 关联起来
    NSManagedObjectModel *model = [NSManagedObjectModel mergedModelFromBundles:nil];
    
    // 持久化存储调度器
    NSPersistentStoreCoordinator *store = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:model];
    
    // 存储数据库的名字
    NSError *error = nil;
    
    // 获取docment目录
    NSString *doc = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    
    // 数据库保存的路径
    NSString *sqlitePath = [doc stringByAppendingPathComponent:@"company.sqlite"];
    
    [store addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:[NSURL fileURLWithPath:sqlitePath] options:nil error:&error];
    
    context.persistentStoreCoordinator = store;
    
    self.context = context;
}

• 基本CRUD

(IBAction)addEmployee:(id)sender {
    
    // 创建员工
    
    Employee *emp1 = [NSEntityDescription insertNewObjectForEntityForName:@"Employee" inManagedObjectContext:self.context];
    
    // 设置员工属性
    emp1.name = @"lisi";
    emp1.age = @28;
    emp1.height = @2.10;
    
    //保存 - 通过上下文操作
    NSError *error = nil;
    [self.context save:&error];
    if (!error) {
        NSLog(@"success");
    }else{
        NSLog(@"%@",error);
    } 
}

  //创建一个请求对象 （填入要查询的表名-实体类）
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Employee"];
 // 查找张三 并且身高大于1.8
//    NSPredicate *pre = [NSPredicate predicateWithFormat:@"name=%@ AND height > %@",@"zhangsan",@(1.8)];//    request.predicate = pre;
    
    //排序 以身高进行升序
//    NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"height" ascending:NO];
//    request.sortDescriptors = @[sort];
 // 分页查询 总共13条数据 每页显示5条数据
    //第一页的数据
    request.fetchLimit = 5;
    request.fetchOffset = 10;
 //读取信息
    NSError *error = nil;
    NSArray *emps = [self.context executeFetchRequest:request error:&error];
    if (!error) {
        NSLog(@"emps: %@",emps);
        for (Employee *emp in emps) {
            NSLog(@"%@ %@ %@",emp.name,emp.age,emp.height);
        }
    }else{
        NSLog(@"%@",error);
    }

-(void)deleteEmployeeWithName:(NSString *)name{
    // 删除zhangsan
    // 1.查找到zhangsan
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Employee"];
    NSPredicate *pre = [NSPredicate predicateWithFormat:@"name=%@",name];
    request.predicate = pre;
    // 2.删除zhangsan
    NSArray *emps = [self.context executeFetchRequest:request error:nil];
    for (Employee *emp in emps) {
        NSLog(@"删除员工的人 %@",emp.name);
        [self.context deleteObject:emp];
    }
    // 3.用context同步下数据库
    //所有的操作暂时都是在内存里，调用save 同步数据库
    [self.context save:nil];
}

 (IBAction)updateEmployee:(id)sender {
    // 把wangwu的身高更改成 1.7
    // 1.查找wangwu
    NSArray *emps = [self findEmployeeWithName:@"wangwu"];
    // 2.更新身高
    if (emps.count == 1) {
        Employee *emp = emps[0];
        emp.height = @1.7;
    }
    // 3.同步（保存）到数据
    [self.context save:nil];
}
#pragma mark 模糊查询
 (IBAction)likeSearcher:(id)sender {
    // 查询
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Employee"];
    // 过滤
    // 1.查询以wang开头员工
    //NSPredicate *pre = [NSPredicate predicateWithFormat:@"name BEGINSWITH %@",@"wang"];
    // 2.以si 结尾
    //NSPredicate *pre = [NSPredicate predicateWithFormat:@"name ENDSWITH %@",@"si"];
    // 3.名字包含 g
    //NSPredicate *pre = [NSPredicate predicateWithFormat:@"name CONTAINS %@",@"g"];
    // 4.like 以si结尾
    NSPredicate *pre = [NSPredicate predicateWithFormat:@"name like %@",@"li*"];
    request.predicate = pre;
    //读取信息
    NSError *error = nil;
    NSArray *emps = [self.context executeFetchRequest:request error:&error];
    if (!error) {
        NSLog(@"emps: %@",emps);
        for (Employee *emp in emps) {
            NSLog(@"%@ %@ %@",emp.name,emp.age,emp.height);
        }
    }else{
        NSLog(@"%@",error);
    }
}