关于coredata 网上的相关资料比较少，大部分是基本用法。于是便找到苹果官方文档进行深入学习。

　　分享一下心得，如果用了coredata 必须懂得 coredata Migration，否则app版本更新 core data model schema 变化很大可能导致持久化coredata 出错，程序崩溃。

　　以下几种情况 可以简单的用  Lightweight Migration 迁移数据到新版本Model, 如下。

　　NSDictionary *options = [NSDictionarydictionaryWithObjectsAndKeys:[NSNumbernumberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, 　　　　[NSNumbernumberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

　　　　_persistentStoreCoordinator = [[NSPersistentStoreCoordinatoralloc] initWithManagedObjectModel:[selfmanagedObjectModel]];

if (![_persistentStoreCoordinatoraddPersistentStoreWithType:NSSQLiteStoreTypeconfiguration:nilURL:storeURL options:options error:&error])

　　//其他代码

--------------几种情况概括如下--------------------

　　　　1,Simple addition of a new attribute.(为某个Entity 添加属性)

　　　　2,Removal of an attribute.(为某个Entity 删除属性)

　　　　3,A non-optional attribute becoming optional.

　　　　4,An optional attribute becoming non-optional, and defining a default value.

　　　　5,Renaming an entity or property.

• Adding relationships and changing the type of relationship

  • You can add a new relationship or delete an existing relationship.

  • Renaming a relationship (by using a renaming identifier, just like an attribute)

  • Changing a relationship from a to-one to a to-many, or a non-ordered to-many to ordered (and visa-versa)

• Changing the entity hierarchy

  • You can add, remove, rename entities

  • You can create a new parent or child entity and move properties up and down the entity hierarchy

  • You can move entities out of a hierarchy。

　　<注意>You cannot, however, merge entity hierarchies; if two existing entities do not share a common parent in the source, they cannot share a common parent in the destination。这种情况不能用轻量迁移。

官方文档：

https://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/CoreDataVersioning/Articles/vmLightweightMigration.html#//apple_ref/doc/uid/TP40004399-CH4-SW1

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