在ios开发中coredata与sqlite数据库操作有什么优势
推荐回答（1个）
转载 sqlite数据库操作的基本流程是, 创建数据库, 再通过定义一些字段来定义表格结构, 可以利用sql语句向表格中插入记录, 删除记录, 修改记录, 表格之间也可以建立联系。
这个过程出现了, 表格的结构(schema), 所有表格的结构和相互联系构成整个数据库的模型, 数据库存放的方式(可以是文件或者在内存), 数据库操作, sql语句(主要是查询), 表格里面的记录。
下面将上面说的文字, 跟CoreData的类作个对应:
表格结构 --> NSEntityDescription
数据库中所有表格和他们的联系 -->NSManagedObjectModel
数据库存放方式 --> NSPersistentStoreCoordinator
数据库操作 --> NSManagedObjectContext
查询语句 --> NSFetchRequest
表格的记录 --> NSManagedObject
可能上面的对应关系并非十分严格, 但确实可以帮助理解.
下面再看看CoreData的类
NSEntityDescription
NSManagedObjectModel
NSEntityDescription用来定义表格结构, 所以你就可以理解NSManagedObjectModel中的setEntities:(NSArray *)entities函数大概有什么用了 . 通常, 定义model, 是用文件CoreData.xcda*****odel, 可以图形化的操作. 这类似用nib来创建界面.
建个工程, 使用coredata, 模拟器运行之后, 程序对应的document目录出现一个CoreData.sqlite. 可以利用sqlite3命令来查看里面的表格结构
用命令行sqlite3 CoreData.sqlite 进入
>.tables
ZEVENT Z_METADATA Z_PRIMARYKEY
可以看到有表格ZEVENT, 对应的CoreData.xcda*****odel文件有名字叫Event的Entity
>.schema ZEVENT
CREATE TABLE ZEVENT ( Z_PK INTEGER PRIMARY KEY, Z_ENT INTEGER, Z_OPT INTEGER, ZTIMES*****P TIMES*****P );
对应的Event中有属性timeS*****p, 可以看到, 相应的ZEVENT表格中有字段TIMES*****P
> select * from ZEVENT
1|1|1|306295807.974966
2|1|1|306295810.981875
3|1|1|306295811.982537
这表格有三个记录, 可以用来初始化三个NSManagedObject, 修改了NSManagedObject, save之后也修改了表格记录
你可以在CoreData.xcda*****odel添加新的entity, 之后用sqlit3命令来查看数据库的变化
NSPersistentStoreCoordinator
这个类的对象通常用NSManagedObjectModel的对象来初始化, 这个类抽象出不同的存放方式, 最经常用的是NSSQLiteStoreType.
NSManagedObjectContext
这个类的对象又用NSPersistentStoreCoordinator的对象来初始化, 它里面有些方法来添加, 删除NSManagedObject
NSFetchRequest
通常用NSEntityDescription来构造查询, 也就指定查询那个表格, 另外可以指定排序.
在CoreData的设计中, 下一层有相应的属性指向上一层, 所以NSManagedObject有属性得到NSEntityDescription, NSEntityDescription有属性得到NSManagedObjectModel.
至于类
NSFetchedResultsController, 只是又封了一下, 和NSFetchRequest合起来使用, 方便取数据, 另外和NSManagedObjectContext关联, 当数据库发生变化的时候收到通知.
这文章只初步梳理了一下CoreData各类的关系, 各类的方法还需要一一研究. 文章最开始说CoreData是对sqlite数据库的一个封装, 不是严格的, CoreData不一定用sqlit来实现, 但他们之间确实有种对应关系。
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