Core Data浅谈系列之二 ： 简略的CURD

Core Data浅谈系列之二 ： 简单的CURD
在上一篇中简单介绍了Core Data Stack，自上而下地对Core Data应用结构有个基本的认识，不过都是理论上的。这里就以上一篇的理论构建起一个可运行的Demo，执行一些简单的增删改查操作。?（图片来自Apple）??首先，我们需要建立如上图的栈结构。因此，在ViewController里添加3个属性：[cpp]?view plaincopy

1. @interface?ViewController?:?UIViewController??
2. ??
3. @property?(nonatomic,?retain)?NSManagedObjectModel?*managedObjectModel;??
4. @property?(nonatomic,?retain)?NSManagedObjectContext?*managedObjectContext;??
5. @property?(nonatomic,?retain)?NSPersistentStoreCoordinator?*persistentStoreCoordinator;??
6. ??
7. @end??

根据前文讨论的顺序，我们首先创建managedObjectModel（在那之前需要引入CoreData Framework）：

[cpp]?view plaincopy

1. -?(NSManagedObjectModel?*)managedObjectModel??
2. {??
3. ????if?(nil?!=?_managedObjectModel)?{??
4. ????????return?_managedObjectModel;??
5. ????}??
6. ??????
7. ????_managedObjectModel?=?[[NSManagedObjectModel?mergedModelFromBundles:nil]?retain];??
8. ????return?_managedObjectModel;??
9. }??

接着创建NSManagedObject的生存环境 —— NSManagedObjectContext：[cpp]?view plaincopy

1. -?(NSManagedObjectContext?*)managedObjectContext??
2. {??
3. ????if?(nil?!=?_managedObjectContext)?{??
4. ????????return?_managedObjectContext;??
5. ????}??
6. ??????
7. ????_managedObjectContext?=?[[NSManagedObjectContext?alloc]?init];??
8. ????return?_managedObjectContext;??
9. }??

由于Demo会将数据存储到本地文件，所以还需要NSPersistentStoreCoordinator和NSManagedObjectContext配合。下面是创建Core Data栈结构的完整代码：[cpp]?view plaincopy

1. #pragma?mark?-???
2. #pragma?mark?-?Core?Data?Stack??
3. ??
4. -?(NSManagedObjectModel?*)managedObjectModel??
5. {??
6. ????if?(nil?!=?_managedObjectModel)?{??
7. ????????return?_managedObjectModel;??
8. ????}??
9. ??????
10. ????_managedObjectModel?=?[[NSManagedObjectModel?mergedModelFromBundles:nil]?retain];??
11. ????return?_managedObjectModel;??
12. }??
13. ??
14. -?(NSManagedObjectContext?*)managedObjectContext??
15. {??
16. ????if?(nil?!=?_managedObjectContext)?{??
17. ????????return?_managedObjectContext;??
18. ????}??
19. ??????
20. ????_managedObjectContext?=?[[NSManagedObjectContext?alloc]?init];??
21. ??????
22. ????if?(self.persistentStoreCoordinator)?{??
23. ????????[_managedObjectContext?setPersistentStoreCoordinator:self.persistentStoreCoordinator];??
24. ????}??
25. ??????
26. ????return?_managedObjectContext;??
27. }??
28. ??
29. -?(NSPersistentStoreCoordinator?*)persistentStoreCoordinator??
30. {??
31. ????if?(nil?!=?_persistentStoreCoordinator)?{??
32. ????????return?_persistentStoreCoordinator;??
33. ????}??
34. ??????
35. ????NSString?*storeType?=?NSSQLiteStoreType;??
36. ????NSString?*storeName?=?@"cdNBA.sqlite";??
37. ??????
38. ????NSError?*error?=?NULL;??
39. ????NSURL?*storeURL?=?[NSURL?fileURLWithPath:[[self?applicationDocumentsDirectory]?stringByAppendingPathComponent:storeName]];??
40. ??????
41. ????_persistentStoreCoordinator?=?[[NSPersistentStoreCoordinator?alloc]?initWithManagedObjectModel:self.managedObjectModel];??
42. ????if?(![_persistentStoreCoordinator?addPersistentStoreWithType:storeType?configuration:nilURL:storeURL?options:nil?error:&error])?{??
43. ????????NSLog(@"Error?:?%@\n",?[error?localizedDescription]);??
44. ????????NSAssert1(YES,?@"Failed?to?create?store?%@?with?NSSQLiteStoreType",?[storeURL?path]);??
45. ????}??
46. ??????
47. ????return?_persistentStoreCoordinator;??
48. }??
49. ??
50. #pragma?mark?-??
51. #pragma?mark?Application's?Documents?Directory??
52. ??
53. -?(NSString?*)applicationDocumentsDirectory??
54. {??
55. ????NSArray?*paths?=?NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,?NSUserDomainMask,?YES);??
56. ????NSString?*basePath?=?([paths?count]?>?0)???[paths?objectAtIndex:0]?:?nil;??
57. ????return?basePath;??
58. }??

在搭建完基础的Core Data栈结构后，就可以写一些简单的CURD代码了：

[cpp]?view plaincopy

1. #pragma?mark?-???
2. #pragma?mark?-?CURD?Operations??
3. ??
4. -?(BOOL)createTeamWithName:(NSString?*)teamName?city:(NSString?*)teamCity??
5. {??
6. ????if?(!teamName?||?!teamCity)?{??
7. ????????return?NO;??
8. ????}??
9. ??????
10. ????NSManagedObject?*teamObject?=?[NSEntityDescription?insertNewObjectForEntityForName:@"Team"?inManagedObjectContext:self.managedObjectContext];??
11. ????[teamObject?setValue:teamName?forKey:@"name"];??
12. ????[teamObject?setValue:teamCity?forKey:@"city"];??
13. ??????
14. ????return?YES;??
15. }??
16. ??
17. -?(NSArray?*)fetchTeamList??
18. {??
19. ????NSFetchRequest?*fetchRequest?=?[[NSFetchRequest?alloc]?init];??
20. ????[fetchRequest?setEntity:[NSEntityDescription?entityForName:@"Team"?inManagedObjectContext:self.managedObjectContext]];??
21. ??????
22. ????NSError?*error?=?NULL;??
23. ????NSArray?*array?=?[self.managedObjectContext?executeFetchRequest:fetchRequest?error:&error];??
24. ????if?(error)?{??
25. ????????NSLog(@"Error?:?%@\n",?[error?localizedDescription]);??
26. ????}??
27. ??????
28. ????[fetchRequest?release],?fetchRequest?=?nil;??
29. ??????
30. ????return?array;??
31. }??

我们可以把读写的代码放到viewDidLoad函数中：

[cpp]?view plaincopy

1. -?(void)viewDidLoad??
2. {??
3. ????[superviewDidLoad];??
4. //?Do?any?additional?setup?after?loading?the?view,?typically?from?a?nib.??
5. ??????
6. ????[self?createTeamWithName:@"Heat"city:@"Miami"];??
7. ????[self?createTeamWithName:@"Lakers"city:@"LA"];??
8. ????[self?saveContext];??
9. ??????
10. ????NSArray?*teamArray?=?[self?fetchTeamList];??
11. ????if?(teamArray)?{??
12. ????????for?(NSManagedObject?*teamObject?in?teamArray)?{??
13. ????????????NSString?*teamName?=?[teamObject?valueForKey:@"name"];??
14. ????????????NSString?*teamCity?=?[teamObject?valueForKey:@"city"];??
15. ????????????NSLog(@"Team?info?:?%@,?%@\n",?teamName,?teamCity);??
16. ????????}??
17. ????}??
18. }??

由于在context中创建的对象只是存在于内存中，所以我们还需要显式地把数据保存到sqlite文件里：

[cpp]?view plaincopy

1. #pragma?mark?-??
2. #pragma?mark?-?Save?Context??
3. ??
4. -?(void)saveContext??
5. {??
6. ????NSError?*error?=?NULL;??
7. ????NSManagedObjectContext?*moc?=?self.managedObjectContext;??
8. ????if?(moc?&&?[moc?hasChanges]?&&?![moc?save:&error])?{??
9. ????????NSLog(@"Error?%@,?%@",?error,?[error?localizedDescription]);??
10. ????????abort();??
11. ????}??
12. }??

最后，就是跑一下Demo，检验一下结果。执行过一次程序后，我们可以搜索下cdNBA.sqlite文件，然后查看里面的数据：??
?同时，控制台也输出了数据：[plain]?view plaincopy

1. 2013-01-16?14:32:52.638?cdNBA[4717:c07]?Team?info?:?Heat,?Miami??
2. 2013-01-16?14:32:52.639?cdNBA[4717:c07]?Team?info?:?Lakers,?LA??

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