1.如果想創建一個帶有coreData的程序,要在項目初始化的時候勾選中
 
2.創建完成之後,會發現在AppDelegate裡多出了幾個屬性,和2個方法
復制代碼 代碼如下:
<span style="font-size:18px;"> 
 
@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext; 
@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel; 
@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator; 
 
- (void)saveContext; 
- (NSURL *)applicationDocumentsDirectory;</span> 

Core Data數據持久化是對SQLite的一個升級，它是ios集成的，在說Core Data之前，我們先說說在CoreData中使用的幾個類。

（1）NSManagedObjectModel(被管理的對象模型)

相當於實體，不過它包含 了實體間的關系

(2)NSManagedObjectContext(被管理的對象上下文)

操作實際內容

作用：插入數據  查詢  更新  刪除

（3）NSPersistentStoreCoordinator(持久化存儲助理)

相當於數據庫的連接器

(4)NSFetchRequest(獲取數據的請求)

相當於查詢語句

(5)NSPredicate(相當於查詢條件)

(6)NSEntityDescription(實體結構)

(7)後綴名為.xcdatamodel的包

裡面的.xcdatamodel文件，用數據模型編輯器編輯

編譯後為.momd或.mom文件，這就是為什麼文件中沒有這個東西，而我們的程序中用到這個東西而不會報錯的原因。

3.如果想創建一個實體對象的話,需要點擊.xcdatamodel,Add Entity,添加想要的字段

4.生成對象文件,command+n,然後選中CoreData裡的NSManagerObjectSubClass進行關聯,選中實體創建

5.添加數據
復制代碼 代碼如下:
Person *newPerson = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:self.managedObjectContext]; 
     
    if (newPerson == nil){ 
        NSLog(@"Failed to create the new person."); 
        return NO; 
    } 
     
    newPerson.firstName = paramFirstName; 
    newPerson.lastName = paramLastName; 
    newPerson.age = [NSNumber numberWithUnsignedInteger:paramAge]; 
    NSError *savingError = nil; 
     
    if ([self.managedObjectContext save:&savingError]){ 
        return YES; 
    } else { 
        NSLog(@"Failed to save the new person. Error = %@", savingError); 
    } 

NSEntityDescription（實體結構）相當於表格結構

6.取出數據查詢
復制代碼 代碼如下:
/* Create the fetch request first */ 
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; 
    /* Here is the entity whose contents we want to read */ 
    NSEntityDescription *entity = 
    [NSEntityDescription 
     entityForName:@"Person" 
     inManagedObjectContext:self.managedObjectContext]; 
    /* Tell the request that we want to read the
     contents of the Person entity */ 
    [fetchRequest setEntity:entity]; 
    NSError *requestError = nil; 
    /* And execute the fetch request on the context */ 
    NSArray *persons = 
    [self.managedObjectContext executeFetchRequest:fetchRequest 
                                             error:&requestError]; 
    /* Make sure we get the array */ 
    if ([persons count] > 0){ 
        /* Go through the persons array one by one */ 
        NSUInteger counter = 1; 
        for (Person *thisPerson in persons){ 
            NSLog(@"Person %lu First Name = %@", 
                  (unsigned long)counter,  
                  thisPerson.firstName);  
            NSLog(@"Person %lu Last Name = %@",  
                  (unsigned long)counter,  
                  thisPerson.lastName); 
            NSLog(@"Person %lu Age = %ld", 
                  (unsigned long)counter, 
                  (unsigned long)[thisPerson.age unsignedIntegerValue]); 
            counter++; 
        } 
    } else { 
        NSLog(@"Could not find any Person entities in the context.");  
    } 

7.刪除數據
復制代碼 代碼如下:
/* Create the fetch request first */ 
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; 
    /* Here is the entity whose contents we want to read */ 
    NSEntityDescription *entity = 
    [NSEntityDescription 
     entityForName:@"Person" 
     inManagedObjectContext:self.managedObjectContext]; 
    /* Tell the request that we want to read the
     contents of the Person entity */ 
    [fetchRequest setEntity:entity]; 
    NSError *requestError = nil; 
    /* And execute the fetch request on the context */ 
    NSArray *persons = 
    [self.managedObjectContext executeFetchRequest:fetchRequest 
                                             error:&requestError]; 
    if ([persons count] > 0){ 
        /* Delete the last person in the array */ 
        Person *lastPerson = [persons lastObject]; 
        [self.managedObjectContext deleteObject:lastPerson]; 
        NSError *savingError = nil; 
        if ([self.managedObjectContext save:&savingError]){ 
            NSLog(@"Successfully deleted the last person in the array."); 
        } else { 
            NSLog(@"Failed to delete the last person in the array."); 
        } 
    } else {  
        NSLog(@"Could not find any Person entities in the context.");  
    }  

8.排序
復制代碼 代碼如下:
<pre code_snippet_id="243955" snippet_file_name="blog_20140319_5_4289257" name="code" class="objc">NSSortDescriptor *ageSort =  
[[NSSortDescriptor alloc] initWithKey:@"age"  
ascending:YES];  
NSSortDescriptor *firstNameSort =  
[[NSSortDescriptor alloc] initWithKey:@"firstName"  
ascending:YES];  
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:  
ageSort,  
firstNameSort, nil nil];  
fetchRequest.sortDescriptors = sortDescriptors; </pre><p></p> 
<pre></pre> 
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<span style="background-color:rgb(255,255,255)"><span style="font-size:18px"><br> 
</span></span></p> 
<span style="background-color:rgb(255,255,255)">注意</span><span style="font-size:18px; background-color:rgb(255,255,255)">ascending:YES 屬性決定排序順序</span><span style="background-color:rgb(255,255,255)"><span style="font-size:18px"><br> 
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