coredata Lightweight Migration 心得

 

 

　　關於coredata 網上的相關資料比較少，大部分是基本用法。於是便找到蘋果官方文檔進行深入學習。

　　分享一下心得，如果用了coredata 必須懂得 coredata Migration，否則app版本更新 core data model schema 變化很大可能導致持久化coredata 出錯，程式崩潰。

　　以下幾種情況 可以簡單的用  Lightweight Migration 遷移資料到新版本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]) 

　　//其他代碼

--------------幾種情況概括如下--------------------

　　　　1,Simple addition of a new attribute.(為某個Entity 添加屬性)

　　　　2,Removal of an attribute.(為某個Entity 刪除屬性)

　　　　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。這種情況不能用輕量遷移。

官方文檔：

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

　　 下篇　《 core data model mapping 》