ios coredata的用法和利弊
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第一部分coredata的用法
先建立一个使用use coredata的工程，
在。xcdatamodeld文件中建立表格并为表格添加属性
为表格添加关系，
下一步生成表格model
其中生成的model：User和Department里面的属性用的是@dynamic
@property有两个对应的词，一个是@synthesize，一个是@dynamic。如果@synthesize和@dynamic都没写，那么默认的就是@syntheszie var = _var;
@synthesize的语义是如果你没有手动实现setter方法和getter方法，那么编译器会自动为你加上这两个方法。
@dynamic告诉编译器,属性的setter与getter方法由用户自己实现，不自动生成。（当然对于readonly的属性只需提供getter即可）。假如一个属性被声明为@dynamic var，然后你没有提供@setter方法和@getter方法，编译的时候没问题，但是当程序运行到instance.var =someVar，由于缺setter方法会导致程序崩溃；或者当运行到 someVar = var时，由于缺getter方法同样会导致崩溃。编译时没问题，运行时才执行相应的方法，这就是所谓的动态绑定。
然后会再appdelegate里自动生成以下代码：
#pragma mark - Core Data stack
@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
//存储在沙盒里的具体位置
- (NSURL *)applicationDocumentsDirectory {
// The directory the application uses to store the Core Data store file. This code uses a directory named eims.CoreDatatest in the application's documents directory.
return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}
//托管对象
- (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:@CoreDatatest withExtension:@momd];
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
return _managedObjectModel;
}
//持久化存储协调器
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
// The persistent store coordinator for the application. This implementation creates and return 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:@CoreDatatest.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;
}
//托管上下文
- (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] init];
[_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();
}
}
}
这些代码知道具体作用就好，如果想自己手动建立起来coredata文件，也可以自己手动写
下面就是在viewcontroller的具体操作，
先引入appdelegate和User，Department的头文件
在viewcontroller里添加
@property (strong, nonatomic)AppDelegate *myAppDelegate;属性
然后，
具体操作，
添加：
User*user = (User*)[NSEntityDescription insertNewObjectForEntityForName:@User inManagedObjectContext:self.myAppDelegate.managedObjectContext];
[user setName:_nametextfield.text];
[user setAge:[NSNumber numberWithInteger:[_agetextfield.text integerValue]]];
[user setSex:_sextextfield.text];
NSError*error;
BOOL isSaveSuccess = [myAppDelegate.managedObjectContext save:&error];//保存（容易忘）
if (!isSaveSuccess) {
NSLog(@Error:%@,error);
_attentiontextview.text = [NSString stringWithFormat:@Error:%@,error];
}else{
NSLog(@Save Successful!);
_attentiontextview.text = @Save Successful!;
}
查询：//数据请求（请求）：命令集
NSFetchRequest*request = [[NSFetchRequest alloc]init];
//NSEntityDescription（实体描述）：表
NSEntityDescription*user = [NSEntityDescription entityForName:@Department inManagedObjectContext:myAppDelegate.managedObjectContext];
[request setEntity:user];
NSError*error;
NSArray*mutablefetchResult = [myAppDelegate.managedObjectContext
executeFetchRequest:request error:&error];
if (mutablefetchResult == nil) {
NSLog(@Error: %@,mutablefetchResult);
}
NSLog(@the count of entry:%lu,[mutablefetchResult count]);
NSString*str = @;
for (Department*user in mutablefetchResult) {
// NSLog(@name:%@------age:%@-------sex:%@,user.name,user.age,user.sex);
// str = [str stringByAppendingFormat:@name:%@------age:%@-------sex:%@ ---depart:%@ ,user.name,user.age,user.sex,user.userrelationship.departmentname];
str = [str stringByAppendingFormat:@name:%@------ ,user.departmentname];
}
NSLog(@str:%@,str);
更新：//NSFetchRequest 数据请求（请求）：命令集
NSFetchRequest*request = [[NSFetchRequest alloc]init];
//NSEntityDescription（实体描述）：表
NSEntityDescription*user = [NSEntityDescription entityForName:@User inManagedObjectContext:myAppDelegate.managedObjectContext];
[request setEntity:user];
//设置查询条件 NSPredicate （谓词）：查询语句
NSPredicate*predicate = [NSPredicate predicateWithFormat:@name == %@,@lisi];
[request setPredicate:predicate];
NSError*error;
NSArray * mutablFetchResult = [myAppDelegate.managedObjectContext executeFetchRequest:request error:&error];
if (mutablFetchResult == nil) {
NSLog(@Error:%@,error);
_attentiontextview.text = [NSString stringWithFormat:@Error:%@,error];
}
NSLog(@the count of entry:%lu,[mutablFetchResult count]);
for (User*user in mutablFetchResult) {
[user setAge:[NSNumber numberWithInteger:999]];
}
//判断是否修改成功
BOOL isSaveSuccess = [myAppDelegate.managedObjectContext save:&error];//保存（容易忘）
if (!isSaveSuccess) {
NSLog(@Error:%@,error);
_attentiontextview.text = [NSString stringWithFormat:@Error:%@,error];
}else{
NSLog(@update Successful!);
_attentiontextview.text = @update Successful!;
}
删除：//数据请求（命令集）
NSFetchRequest*request = [[NSFetchRequest alloc]init];
//实体描述（表）
NSEntityDescription*user = [NSEntityDescription entityForName:@Department inManagedObjectContext:myAppDelegate.managedObjectContext];
[request setEntity:user];
//设置查询条件
NSPredicate* predicate = [NSPredicate predicateWithFormat:@departmentname == %@,@公共事业部];
[request setPredicate:predicate];
NSError*error;
NSArray*mutableFetchResult = [myAppDelegate.managedObjectContext executeFetchRequest:request error:&error];
if (mutableFetchResult == nil) {
NSLog(@Error:%@,error);
_attentiontextview.text = [NSString stringWithFormat:@Error:%@,error];
}
NSLog(@mutableFetchResult %lu,[mutableFetchResult count]);
for (User*user in mutableFetchResult) {
[myAppDelegate.managedObjectContext deleteObject:user];
}
//判断是否删除成功
BOOL isDeleteSuccess = [myAppDelegate.managedObjectContext save:&error];//保存（容易忘）
if (!isDeleteSuccess) {
NSLog(@Error:%@,error);
_attentiontextview.text = [NSString stringWithFormat:@Error:%@,error];
}else{
NSLog(@delete Successful!);
_attentiontextview.text = @delete Successful!;
}
coredata并非严格的说是对sqlite数据库的一个封装，也可以用其他的数据库，并不一定要使用sqlite3，当然了coredata的好处还是非常多的，高效，简介，能节省至少50%的代码量，条目清新
对于iOS开发者来说，会使用Core Data是一项必备技能。 没有它，很多app都不会存在。当在互联网上四处搜索Core Data学习教程，你很容易被各种各样的术语吓倒。事实上大部分学习教程都首先假定你已经知道了这些术语，而如果你不了解这些术语，那将会陷入困惑中。所以首先要知道关键的术语
