CoreData的使用

第一步：创建一个 DataDemo.xcdatamodel 文件，在其中建一个实体名字为 Entity1 ，实体中建两个字段 id 和 name。

第二步：为项目添加 CoreData.framework 框架，然后在 .pch 中加入 #import <coredata/coredata.h>

第三步：在 app delegate 中定义 core data 的相关对象（同时完成它们的初始化工作）

.h 文件：

#import <coredata/coredata.h>

@private    
    NSManagedObjectModel *managedObjectModel;
    NSManagedObjectContext *managedObjectContext;
    NSPersistentStoreCoordinator *persistentStoreCoordinator;

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

- (NSString*) applicationDocumentsDirectory;
- (void) saveContext;

.m 文件：

@synthesize managedObjectModel;
@synthesize managedObjectContext;
@synthesize persistentStoreCoordinator;

- (void)dealloc {
    [managedObjectModel release];
    [managedObjectContext release];
    [persistentStoreCoordinator release];
    [super dealloc];
}

- (NSString*)applicationDocumentsDirectory
{ 
    //return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *basePath = ([paths count] > 0) ? [paths objectAtIndex:0] : nil;
    return basePath;
    //return [NSURL URLWithString:basePath];
}

- (void)saveContext{     
   NSError *error = nil;    
   NSManagedObjectContext *objectContext = self.managedObjectContext;    
   if (objectContext != nil)    
   {        
 if ([objectContext hasChanges] && ![objectContext save:&error])      
 { 
  NSLog(@"Unresolved error %@, %@", error, [error userInfo]);        
  abort();      
 }    
   }
}

- (NSManagedObjectContext *)managedObjectContext
{
    if (managedObjectContext != nil) {
        return managedObjectContext;
    }
    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {
        managedObjectContext = [[NSManagedObjectContext alloc] init];
        [managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return managedObjectContext;
}

- (NSManagedObjectModel *)managedObjectModel 
{
    if (managedObjectModel != nil) {
        return managedObjectModel;
    }
    //从本地所有 xcdatamodel 文件中获得这个 CoreData 的数据模板
    managedObjectModel = [[NSManagedObjectModel mergedModelFromBundles:nil] retain];
    return managedObjectModel;
}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator 
{
    if (persistentStoreCoordinator != nil) {
        return persistentStoreCoordinator;
    }
    //数据库名为TestDB.sqlite
    NSURL *storeUrl = [NSURL fileURLWithPath:[[self applicationDocumentsDirectory] stringByAppendingPathComponent:@"TestDB.sqlite"]];
    NSError *error;
    persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nilURL:storeUrl options:nil error:&error]) {
        NSAssert(0, @"persistentStoreCoordinator init failed!");
    }
    return persistentStoreCoordinator;
}

- (void)applicationWillTerminate:(UIApplication *)application
{
    NSError *error;
    if (managedObjectContext != nil) {
        if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
            NSAssert(0, @"save changes failed when terminage application!");
        }
    }
}

第四步：在相关的 viewcontroller 中操作数据，基本的 core data 操作代码如下：

 NSError *error;
 testSQLiteAppDelegate *app = (testSQLiteAppDelegate*)[[UIApplication sharedApplication] delegate];
 NSManagedObjectContext *context = app.managedObjectContext;
 
 //1、插入
 NSManagedObject *newManagedObject  = nil;
 newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:@"Entity1" inManagedObjectContext:context];
 [newManagedObject setValue:[NSNumber numberWithInt:1] forKey:@"id"];
 [newManagedObject setValue:@"i love you" forKey:@"name"];
 if (![context save:&error]){
    NSLog (@"The error is: %@", [error userInfo]);
 }
 else
 {
    NSLog (@"The newManagedObject's id is: %@", [newManagedObject valueForKey:@"id"]);
 }

 //2、查询
 NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
 NSEntityDescription *entity = [NSEntityDescription entityForName:@"Entity1" inManagedObjectContext:context];
 NSSortDescriptor *sortDescriptor1 = [[NSSortDescriptor alloc] initWithKey:@"id" ascending:YES];
 NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
 NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor1, sortDescriptor2, nil];
 [fetchRequest setSortDescriptors:sortDescriptors];
 [fetchRequest setEntity:entity];
 [fetchRequest setFetchBatchSize:20];
 NSArray *objects = [context executeFetchRequest: fetchRequest error:&error];
 if (objects == nil)
 {
     NSLog(@"There was an error!");
 }
 else {
    for (NSManagedObject *oneObject in objects)
    {
       NSLog(@"%@",[oneObject valueForKey:@"name"]);
    }         
 }

 //3、删除
 [context deleteObject:[objects objectAtIndex:0]];
 if (![context save:&error]) {
      exit(-1);
 }

这里更详细的补充一点关于 core data 的操作代码：

1、条件过滤:选择 cid=1 的数据

 - (NSFetchedResultsController*) fetchedResultsController 
 {     
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"cid=1"];     
    [fetchRequest setPredicate:predicate]; 
 }

2、通用代码，在 viewcontroller 里面会用到：

TestViewController.h 的代码：

@interface TestViewController : UITableViewController <NSFetchedResultsControllerDelegate> 
{     
    NSFetchedResultsController *fetchedResultsController;
    NSManagedObjectContext *managedObjectContext;       
}  

@property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController;

@property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;  

- (void)configureCell:(UITableViewCell *)cell withCategory:(Category *)category;

@end

TestViewController.m 的代码：

 -(NSFetchedResultsController *)fetchedResultsController 
 {     
     if (fetchedResultsController != nil) 
     {     
          return fetchedResultsController; 
     }     
     NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];     
     NSEntityDescription *entity = [NSEntityDescription entityForName:@"Category" inManagedObjectContext:managedObjectContext];   
     [fetchRequest setEntity:entity];          
     NSSortDescriptor *nameDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];     
     NSArray *arraySortDescriptor = [[NSArray alloc] initWithObjects:nameDescriptor, nil];    
     [fetchRequest setSortDescriptors:arraySortDescriptor];           
     NSPredicate *predicate = [NSPredicate predicateWithFormat:cidString];     
     [fetchRequest setPredicate:predicate];           
     NSFetchedResultsController *frController =  [[NSFetchedResultsController alloc] 
     initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:@"name" cacheName:@"Root"];     
     frController.delegate = self; 
     self.fetchedResultsController = frController;           
     [frController release];     
     [fetchRequest release];     
     [nameDescriptor release];           
     return fetchedResultsController; 
 }
 
 - (void)controllerWillChangeContent:(NSFetchedResultsController *)
 {     
    [self.tableView beginUpdates];  
 }   
 
 - (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject 
   atIndexPath:(NSIndexPath *)indexPath forChangeType: (NSFetchedResultsChangeType)type 
   newIndexPath:(NSIndexPath *)newIndexPath 
   {     
      UITableView *tableView = self.tableView;     
      switch (type) {         
          case NSFetchedResultsChangeInsert:        
               [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];             
                break;                       
          case NSFetchedResultsChangeDelete:             
               [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];             
               break;                       
          case NSFetchedResultsChangeMove:             
              [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];                           

             [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];             
               break;                   
          case NSFetchedResultsChangeUpdate:             
               [self configureCell:[tableView cellForRowAtIndexPath:indexPath] withCategory:anObject];          
               break;                       
          default:             
               break;     
       } 
   }
   
- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo 
      atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type 
   {           
       switch(type) {                       
             case NSFetchedResultsChangeInsert:             
                 [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];                   

            break;                       
             case NSFetchedResultsChangeDelete:             
                 [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];                   

            break;     
        } 
    }   
    
   - (void) controllerDidChangeContent:(NSFetchedResultsController *)controller 
   {     
        [self.tableView endUpdates];
   }