Core Data数据持久化的使用

CoreData 是ios中用来对数据做持久化的一个框架，它对sqlite进行了封装，使我们不需要学习数据库知识，也不要写SQL语句就能将数据保存到数据库。下面来介绍CoreData的如何使用。

 

1. 新建一个项目，勾选使用Core Data, 新建后需要导入：CoreData.framework

 

 

2.新建项目后，AppDelegate类会生成三个属性

 

@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;
@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;

 

这三个对象操作数据会用的到。

3.新建一个实体对象

 

4. 创建一个类与实体对象关联

5. 保存一个实体模型对象

 

Person *person = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:self.managedObjectContext];
person.personId = @10002;
person.age = @29;
person.name = [NSString stringWithFormat:@"jack"];

NSError *error = nil;
BOOL ret = [self.managedObjectContext save:&error];
if (ret) {
    NSLog(@"保存成功!");
} else {
    NSLog(@"error");
}

6.删除一个实体模型对象

 

 

//删除
- (void)modifyPerson {
    NSEntityDescription *entifyDesc = [NSEntityDescription entityForName:@"Person" inManagedObjectContext:self.managedObjectContext];
    NSFetchRequest *fetchReqeust = [[NSFetchRequest alloc] init];
    [fetchReqeust setEntity:entifyDesc];

    //查询年龄大于30的实体person对象
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"self.age=30"];
    [fetchReqeust setPredicate:predicate];
    //查询出来的person对象数组
    NSArray *persons = [self.managedObjectContext executeFetchRequest:fetchReqeust error:nil];
    //遍历删除
    for (Person *p in persons) {
        [self.managedObjectContext deleteObject:p];
    }

}

7. 查询

 

 

//根据条件查询数据
- (void)queryPerson {
    NSEntityDescription *entifyDesc = [NSEntityDescription entityForName:@"Person" inManagedObjectContext:self.managedObjectContext];
    //查询对象
    NSFetchRequest *fetchReqeust = [[NSFetchRequest alloc] init];
    [fetchReqeust setEntity:entifyDesc];

    //查询条件
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"self.age>40 && self.personId>10015"];
    [fetchReqeust setPredicate:predicate];

    //排序，按age降序排列
    NSSortDescriptor *sortDesc = [NSSortDescriptor sortDescriptorWithKey:@"age" ascending:NO];
    [fetchReqeust setSortDescriptors:@[sortDesc]];

    //查询
    NSArray *persons = [self.managedObjectContext executeFetchRequest:fetchReqeust error:nil];
    for (Person *p in persons) {
        NSLog(@"name=%@,age=%@,id=%@",p.name,p.age,p.personId);
    }
}

参考资料：
Core Data Reference API listing for the Core Data classes
http://developer.apple.com/documentation/Cocoa/Reference/CoreData_ObjC/index.html

NSPredicate Reference API listing for NSPredicate
http://developer.apple.com/documentation/Cocoa/Reference/Foundation/ObjC_classic/Classes/NSPredicate.html