為什么80%的碼農(nóng)都做不了架構(gòu)師？>>> ??

????首先說說對于CoreData的理解，類似于FMDB。他能將數(shù)據(jù)庫中的列表轉(zhuǎn)換成模型實體對象，方便開發(fā)者使用。同時，也能將一個將實體對象轉(zhuǎn)換成數(shù)據(jù)庫中的表，存儲到數(shù)據(jù)庫中。這就是CoreData,數(shù)據(jù)庫與實體模型之間的轉(zhuǎn)換工具。

????打開的沙盒的Library路徑，你會發(fā)現(xiàn)，如下的文件目錄：（前提是你的工程里面使用了CoreData）

由此可以證明，CoreData類似FMDB，都是基于sqlite進(jìn)行數(shù)據(jù)存儲的。

????由于Xcode升級到8.x，CoreData的使用與以往之間會有所不同。這里先記下自己軌跡。

??? 首先在創(chuàng)建工程的時候，選中Use CoreData。

??? 這時候打開工程，會發(fā)現(xiàn)Appdelegate里面會多了以下的東西：

@property (readonly, strong) NSPersistentContainer *persistentContainer;- (void)saveContext; #pragma mark - Core Data stack@synthesize persistentContainer = _persistentContainer;- (NSPersistentContainer *)persistentContainer {@synchronized (self) {if (_persistentContainer == nil) {_persistentContainer = [[NSPersistentContainer alloc] initWithName:@"SmartOffice"];[_persistentContainer loadPersistentStoresWithCompletionHandler:^(NSPersistentStoreDescription *storeDescription, NSError *error) {if (error != nil) {NSLog(@"Unresolved error %@, %@", error, error.userInfo);abort();}}];}}return _persistentContainer; }#pragma mark - Core Data Saving support- (void)saveContext {NSManagedObjectContext *context = self.persistentContainer.viewContext;NSError *error = nil;if ([context hasChanges] && ![context save:&error]) {NSLog(@"Unresolved error %@, %@", error, error.userInfo);abort();} }

??? 而之前的版本會多出來這么寫東西：

@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext; @property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel; @property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;- (void)saveContext; - (NSURL *)applicationDocumentsDirectory; #pragma mark - Core Data stack@synthesize managedObjectContext = _managedObjectContext; @synthesize managedObjectModel = _managedObjectModel; @synthesize persistentStoreCoordinator = _persistentStoreCoordinator;- (NSURL *)applicationDocumentsDirectory {// The directory the application uses to store the Core Data store file. This code uses a directory named "com.try.SmartHome" in the application's documents directory.return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject]; }- (NSManagedObjectModel *)managedObjectModel {// The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.if (_managedObjectModel != nil) {return _managedObjectModel;}NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"SmartHome" withExtension:@"momd"];_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];return _managedObjectModel; }- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {// The persistent store coordinator for the application. This implementation creates and returns a coordinator, having added the store for the application to it.if (_persistentStoreCoordinator != nil) {return _persistentStoreCoordinator;}// Create the coordinator and store_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"SmartHome.sqlite"];NSError *error = nil;NSString *failureReason = @"There was an error creating or loading the application's saved data.";if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {// Report any error we got.NSMutableDictionary *dict = [NSMutableDictionary dictionary];dict[NSLocalizedDescriptionKey] = @"Failed to initialize the application's saved data";dict[NSLocalizedFailureReasonErrorKey] = failureReason;dict[NSUnderlyingErrorKey] = error;error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:9999 userInfo:dict];// Replace this with code to handle the error appropriately.// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.NSLog(@"Unresolved error %@, %@", error, [error userInfo]);abort();}return _persistentStoreCoordinator; }- (NSManagedObjectContext *)managedObjectContext {// Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.)if (_managedObjectContext != nil) {return _managedObjectContext;}NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];if (!coordinator) {return nil;}_managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];[_managedObjectContext setPersistentStoreCoordinator:coordinator];return _managedObjectContext; }#pragma mark - Core Data Saving support- (void)saveContext {NSManagedObjectContext *managedObjectContext = self.managedObjectContext;if (managedObjectContext != nil) {NSError *error = nil;if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {// Replace this implementation with code to handle the error appropriately.// abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.NSLog(@"Unresolved error %@, %@", error, [error userInfo]);abort();}} }

??? 很明顯的一點就是Xcode升級到8.x的時候?qū)oreData又進(jìn)行了進(jìn)一步的優(yōu)化，精簡了很多。

??? 接下來就是創(chuàng)建Entity，創(chuàng)建屬性，這些都沒有什么變化。

??? 在選中Editor->Create NSManagerObject Subclass...的時候，出來了兩個類，四個文件。這四個文件如下：（比如我是創(chuàng)建的User表的）

User+CoreDataClass.h User+CoreDataClass.m User+CoreDataProperties.h User+CoreDataProperties.m

而之前生成的文件是這樣的：

SHUser.h SHUser.m SHUserInfo.h SHUserInfo.m

當(dāng)你將這些文件導(dǎo)出完畢之后，進(jìn)行編譯。會發(fā)現(xiàn)編譯出錯，link command failed。

在我排除了未添加CoreData依賴褲這個錯誤的時候，我嘗試了一下這個辦法：

???

????就是將每一個實體類的Codegen都設(shè)置成Manual/None，然后保存，重新又導(dǎo)出了一遍，再此編譯。可是又出現(xiàn)了錯誤:File not found?？吹竭@個錯誤，我突然感覺輕松了些許。既然文件找不到，我就來看看哪個文件丟了。具體如圖：

這明明是系統(tǒng)自己導(dǎo)出來的，為什么還會報錯了？？差了很多資料，最終給自己的解釋就是，這是Xcode8.x的一個Bug。直接將報錯的這句話注視了就可以了，或者將 #import "House.h" 改成#import "House+CoreDataClass.h"即可。修改完畢，再次編譯一邊。果然，很順利的就跑通了。

接下來就是如何使用CoreData了，操作數(shù)據(jù)庫不外乎這四種:

增：

刪：

查：

改：

建議，最后建一個Manager，管理著數(shù)據(jù)庫的增刪查改。

如有不足，歡迎指正。

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轉(zhuǎn)載于:https://my.oschina.net/Atoman/blog/801397

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