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詳解iOS應(yīng)用開(kāi)發(fā)中Core Data數(shù)據(jù)存儲(chǔ)的使用

 更新時(shí)間：2016年02月19日 09:24:03   作者：蘋(píng)果吧  
這篇文章主要介紹了iOS應(yīng)用開(kāi)發(fā)中Core Data數(shù)據(jù)存儲(chǔ)的使用,Core Data可以看作是一個(gè)內(nèi)嵌型數(shù)據(jù)庫(kù)SQLite的iOS專用版本,需要的朋友可以參考下

1.如果想創(chuàng)建一個(gè)帶有coreData的程序,要在項(xiàng)目初始化的時(shí)候勾選中
201621991854283.png (129×29) 
2.創(chuàng)建完成之后,會(huì)發(fā)現(xiàn)在AppDelegate里多出了幾個(gè)屬性,和2個(gè)方法

復(fù)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(shù)據(jù)持久化是對(duì)SQLite的一個(gè)升級(jí)，它是ios集成的，在說(shuō)Core Data之前，我們先說(shuō)說(shuō)在CoreData中使用的幾個(gè)類。

（1）NSManagedObjectModel(被管理的對(duì)象模型)

相當(dāng)于實(shí)體，不過(guò)它包含 了實(shí)體間的關(guān)系

(2)NSManagedObjectContext(被管理的對(duì)象上下文)

操作實(shí)際內(nèi)容

作用：插入數(shù)據(jù)  查詢  更新  刪除

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

相當(dāng)于數(shù)據(jù)庫(kù)的連接器

(4)NSFetchRequest(獲取數(shù)據(jù)的請(qǐng)求)

相當(dāng)于查詢語(yǔ)句

(5)NSPredicate(相當(dāng)于查詢條件)

(6)NSEntityDescription(實(shí)體結(jié)構(gòu))

(7)后綴名為.xcdatamodel的包

里面的.xcdatamodel文件，用數(shù)據(jù)模型編輯器編輯

編譯后為.momd或.mom文件，這就是為什么文件中沒(méi)有這個(gè)東西，而我們的程序中用到這個(gè)東西而不會(huì)報(bào)錯(cuò)的原因。


3.如果想創(chuàng)建一個(gè)實(shí)體對(duì)象的話,需要點(diǎn)擊.xcdatamodel,Add Entity,添加想要的字段

201621991919438.png (480×532)201621991939856.png (380×135)

4.生成對(duì)象文件,command+n,然后選中CoreData里的NSManagerObjectSubClass進(jìn)行關(guān)聯(lián),選中實(shí)體創(chuàng)建

201621992014263.png (325×107)

5.添加數(shù)據(jù)

復(fù)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(shí)體結(jié)構(gòu)）相當(dāng)于表格結(jié)構(gòu)

6.取出數(shù)據(jù)查詢

復(fù)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(shù)據(jù)

復(fù)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(fù)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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<p style="background-color:rgb(255,255,255); margin:10px auto; padding-top:0px; padding-bottom:0px; font-family:verdana,'ms song',Arial,Helvetica,sans-serif; line-height:19.09090805053711px"> 
<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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