详解iOS应用开发中Core Data数据存储的使用

1.如果想创建一个带有coreData的程序,要在项目初始化的时候勾选中
 
2.创建完成之后,会发现在AppDelegate里多出了几个属性,和2个方法

代码如下:

<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数据持久化是对SQLite的一个升级，它是ios集成的，在说Core Data之前，我们先说说在CoreData中使用的几个类。

（1）NSManagedObjectModel(被管理的对象模型)

相当于实体，不过它包含 了实体间的关系

(2)NSManagedObjectContext(被管理的对象上下文)

操作实际内容

作用：插入数据  查询  更新  删除

（3）NSPersistentStoreCoordinator(持久化存储助理)

相当于数据库的连接器

(4)NSFetchRequest(获取数据的请求)

相当于查询语句

(5)NSPredicate(相当于查询条件)

(6)NSEntityDescription(实体结构)

(7)后缀名为.xcdatamodel的包

里面的.xcdatamodel文件，用数据模型编辑器编辑

编译后为.momd或.mom文件，这就是为什么文件中没有这个东西，而我们的程序中用到这个东西而不会报错的原因。

3.如果想创建一个实体对象的话,需要点击.xcdatamodel,Add Entity,添加想要的字段

4.生成对象文件,command+n,然后选中CoreData里的NSManagerObjectSubClass进行关联,选中实体创建

5.添加数据

代码如下:

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（实体结构）相当于表格结构

6.取出数据查询


代码如下:

/* 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.删除数据

代码如下:

/* 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

代码如下:

<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> 
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<span style="background-color:rgb(255,255,255)">注意</span><span style="font-size:18px; background-color:rgb(255,255,255)">ascending:YES 属性决定排序顺序</span><span style="background-color:rgb(255,255,255)"><span style="font-size:18px"><br> 
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