[iOS]Core Data淺析二 -- 轉換實體(Entity)爲模型對象

在上篇文章中,筆者寫了如何建立Core Data項目,以及建立數據模型,沒有閱讀的小夥伴請移步,先了解一下相關內容吧: [ [iOS]Core Data淺析(一) ](https://segmentfault.com/a/11... ;
今天,咱們來討論,如何將建立的可視化模型,轉化爲OC的對象模型.
接着咱們上一個工程繼續操做;

一. 轉化爲對象模型

來到咱們的LZCoreData.xcdatamodeld文件,選中PeopleEntity實體,而後點擊Xcode導航欄的File-->New -->File...或者直接command+N,新建文件,選擇Core Data-->NSManagedObject subclass

Next-->Next.來到以下界面:

這裏會顯示項目中全部待轉化爲模型的實體列表,選擇你要轉化的實體,繼續Next-->Create;
這時,項目的左側導航會多了幾個文件:

就是分別爲PeopleEntit和ManEntity建立的模型文件,這裏咱們主要用到的是那四個名稱比較長的類目文件;
這裏有一個問題,須要咱們手動處理一下:

比較這兩個類目文件,咱們會發現,在PeopleEntity+CoreDataProperties.h文件中的manRelationship屬性被聲明爲了NSManagedObject類型,而咱們建立的模型中這個屬性類型是ManEntity,這是不對的;而在ManEntity+CoreDataProperties.h文件中的peopleRelationship是PeopleEntity類型的,是正確的;這是由於在生成PeopleEntity的模型的時候ManEntity的模型並不存在,因此係統不知道有這個類型,就直接聲明爲NSManagedObject類型;而在生成ManEntity的模型的時候,PeopleEntity的模型已經存在了,因此他的屬性聲明是正常的;
這時,只須要咱們手動改一下PeopleEntity+CoreDataProperties.h的屬性manRelationship的類型爲ManEntity便可;

改完後,一編譯發現報錯了,這是由於缺乏對ManEntity的引用,這裏咱們並不須要直接訪問ManEntity的屬性,因此只須要在PeopleEntity.h中加上:

@class ManEntity;

再編譯,就沒有問題了;

二. 使用對象模型

模型轉化完成,就能夠在咱們的代碼中使用了,
來到咱們的ViewController.m文件,
導入頭文件PeopleEntity+CoreDataProperties.h
和ManEntity+CoreDataProperties.h,
並修改成如下代碼:

//獲取代理
    AppDelegate *delegate = [[UIApplication sharedApplication] delegate];
    //獲取context
    NSManagedObjectContext *context = [delegate managedObjectContext];
    
    //獲取PeopleEntity實體
    //這裏修改成PeopleEntity類型
    PeopleEntity *people = [NSEntityDescription insertNewObjectForEntityForName:@"PeopleEntity" inManagedObjectContext:context];
    
    //設置屬性內容
    people.name = @"流火緋瞳";
    people.age = @27;
    people.sex = @0;
//    [people setValue:@"流火緋瞳" forKey:@"name"];
//    [people setValue:@26 forKey:@"age"];
//    [people setValue:@0 forKey:@"sex"];
    
    //獲取ManEntit實體
    //這裏修改成ManEntity類型
    ManEntity *man = [NSEntityDescription insertNewObjectForEntityForName:@"ManEntity" inManagedObjectContext:context];
    
    man.height = @178.0;
    man.weight = @60.0;
    man.name = @"張三丰";
    man.peopleRelationship = people;
    
//    [man setValue:@178.0 forKey:@"height"];
//    [man setValue:@60.0 forKey:@"weight"];
//    [man setValue:@"張三" forKey:@"name"];
//    [man setValue:people forKey:@"peopleRelationship"];
//    
//    [people setValue:man forKey:@"manRelationship"];
    
    people.manRelationship = man;
    
    NSError *error;
    //保存更改
    if ([context save:&error]) {
        NSLog(@"保存成功");
    } else {
        NSLog(@"Whoops, couldn't save: %@", [error localizedDescription]);
    }
    
    //查詢實體
    //建立一個查詢請求
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    //獲取要查詢的實體
    NSEntityDescription *entity = [NSEntityDescription
                                   entityForName:@"PeopleEntity" inManagedObjectContext:context];
    //添加到查詢請求
    [fetchRequest setEntity:entity];
    //開始查詢並獲取結果
    NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
    
    NSLog(@"輸出查詢結果");
    for (PeopleEntity *info in fetchedObjects) {
        
        NSLog(@"Name: %@", info.name);
        NSLog(@"age: %@", info.age);
        NSLog(@"sex: %@", info.sex);
        NSLog(@"-----------------------------------");

        
//        NSLog(@"Name: %@", [info valueForKey:@"name"]);
//        NSLog(@"age: %@", [info valueForKey:@"age"]);
//        NSLog(@"sex: %@", [info valueForKey:@"sex"]);
//        NSLog(@"-----------------------------------");
        
        ManEntity *man1 = [info valueForKey:@"manRelationship"];
        
        
        NSLog(@"Name: %@", man1.name);
        NSLog(@"weight: %@", man1.weight);
        NSLog(@"height: %@", man1.height);
        NSLog(@"==========================================");

//        NSLog(@"Name: %@", [man1 valueForKey:@"name"]);
//        NSLog(@"weight: %@", [man1 valueForKey:@"weight"]);
//        NSLog(@"height: %@", [man1 valueForKey:@"height"]);
//        NSLog(@"==========================================");
    }

爲了便於比較先後作了哪些更改,這裏我沒有把原來的KVC模式賦值取值方法刪除,只是註釋掉了;並添加了咱們熟悉的對象屬性賦值取值方式;
運行一下看看結果吧:

2016-05-26 16:22:27.286 LZCoreData[5765:594436] 保存成功
2016-05-26 16:22:27.288 LZCoreData[5765:594436] 輸出查詢結果
2016-05-26 16:22:27.288 LZCoreData[5765:594436] Name: 流火緋瞳
2016-05-26 16:22:27.288 LZCoreData[5765:594436] age: 26
2016-05-26 16:22:27.288 LZCoreData[5765:594436] sex: 0
2016-05-26 16:22:27.288 LZCoreData[5765:594436] -----------------------------------
2016-05-26 16:22:27.289 LZCoreData[5765:594436] Name: 張三
2016-05-26 16:22:27.289 LZCoreData[5765:594436] weight: 60
2016-05-26 16:22:27.289 LZCoreData[5765:594436] height: 178
2016-05-26 16:22:27.290 LZCoreData[5765:594436] ==========================================
2016-05-26 16:22:27.290 LZCoreData[5765:594436] Name: 流火緋瞳
2016-05-26 16:22:27.290 LZCoreData[5765:594436] age: 27
2016-05-26 16:22:27.290 LZCoreData[5765:594436] sex: 0
2016-05-26 16:22:27.290 LZCoreData[5765:594436] -----------------------------------
2016-05-26 16:22:27.290 LZCoreData[5765:594436] Name: 張三丰
2016-05-26 16:22:27.290 LZCoreData[5765:594436] weight: 60
2016-05-26 16:22:27.290 LZCoreData[5765:594436] height: 178
2016-05-26 16:22:27.308 LZCoreData[5765:594436] ==========================================

什麼?有兩組數據!! 若是你是接着上篇文章作的,這裏固然會輸出兩組數據,由於咱們保存了兩次數據嘛.由可視化的模型轉化爲對象模型到這裏就完成了,而後就能夠在項目中使用了.固然,到目前爲止,咱們只是介紹了Core Data的使用準備工做,真正使用的話,咱們須要完善他的增刪改查功能;