CoreData的简单使用

一.基础知识：

CoreData是对SQLite的封装，使用的时候比较方便，减少对SQL语句的使用。

CoreData中的核心对象

NSManagedObjectModel:代表Core Data 的模型文件，包含模型的数据结构;

NSManagedObjectContext:负责应用和数据库之间的交互(CRUD);

NSPersistentStoreCoordinator:添加持久的数据存储仓库,通常采用NSManagedObjectModel的对象来初始化，最经常用的是NSSQLiteStoreType;

NSEntityDescription:用来描述实体对象的;

Entity:定义一个实体;

Attribute:实体的一个属性;

Relationship:关联实体;

NSFetchRequest:用来设置一个查询的请求，可以指定查询顺序;

Predicate:设置查询的条件;

Sort Descriptor:设置排序。

二.具体步骤：

1.打开Xcode，按住shift+command+N新建一个工程，勾选 Use Core Data：

2.在Appdelegate.h和.m文件中  会自动生成以下文件：

#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;
@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;

- (void)saveContext;
- (NSURL *)applicationDocumentsDirectory;

@end

Appdelegate.m文件

#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.zhangyu.CoreDataTwo" 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:@"CoreDataTwo" withExtension:@"momd"];
    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    return _managedObjectModel;
}

- (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:@"CoreDataTwo.sqlite"];
    NSLog(@"---url:%@",storeURL);
    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] 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();
        }
    }
}

在工程文件中还会看到红色选框中的文件：然后单击打开创建一个model,我在这里创建一个Users，并添加相应的属性user_name,user_password两个属性，声明为字符串类型。

之后选择Editor-》Create NSManagedObject SubClass创建 会在工程里直接生成Users.h和Users.m文件。

4.准备条件完成后在Storyboard中设置两个Label和两个TextField、一个segmentControl控件，并拖拉控件在ViewControloler.h中：

@interface ViewController : UIViewController
@property (weak, nonatomic) IBOutlet UITextField *username;
@property (weak, nonatomic) IBOutlet UITextField *password;

- (IBAction)segmentControl:(UISegmentedControl *)sender;

之后在ViewController中编写相应的代码：

#import "ViewController.h"
#import "AppDelegate.h"
#import "Users.h"
@interface ViewController ()
@property (nonatomic,strong)AppDelegate *myDelegate;
@property(nonatomic,strong) NSMutableArray *users;
@property(nonatomic,assign)BOOL query;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    self.myDelegate = [UIApplication sharedApplication].delegate;
    self.query = NO;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)segmentControl:(UISegmentedControl *)sender {

    switch (sender.selectedSegmentIndex) {
        case 0:
             [self queryFromDB];
            break;
        case 1:[self addToDB];
            break;
        default:
            break;
    }
}

-(void)addToDB{
    //@prames entityForName参数要与所建的Entity保持一致，如建的实体是Users
    Users *us = [NSEntityDescription insertNewObjectForEntityForName:@"Users" inManagedObjectContext:self.myDelegate.managedObjectContext];
    us.user_name = self.username.text;//或者这种写法[us setValue:@"user_name" forKey:self.username.text];

        us.user_password = self.password.text;

    NSError *error;
    //托管对象准备好后，调用托管对象上下文的save方法将数据写入数据库
    BOOL isSaveSuccess = [self.myDelegate.managedObjectContext save:&error];
    if (!isSaveSuccess) {

        [NSException raise:@"访问数据库错误" format:@"%@",[error localizedDescription]];
        NSLog(@"Error: %@,%@",error,[error userInfo]);
    }else{
        NSLog(@"Save successful!");
    }
}
#pragma mark - 从数据库中查询数据
-(void)queryFromDB{

    //创建取回数据请求
    NSFetchRequest *request = [[NSFetchRequest alloc]init];
    //设置要查询哪种实体的实体对象
    //@prames entityForName参数要与所建的Entity保持一致
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Users" inManagedObjectContext:self.myDelegate.managedObjectContext];
    //设置请求实体
    [request setEntity:entity];

    //指定按照什么的排序方式，无排序
    NSSortDescriptor *sort = [[NSSortDescriptor alloc]initWithKey:@"user_name" ascending:NO];
    NSArray *sortDescriptions = [[NSArray alloc]initWithObjects:sort, nil];
    [request setSortDescriptors:sortDescriptions];

    NSError *error;
    //执行获取数据请求，返回数组
    NSMutableArray *mutableFetch = [[self.myDelegate.managedObjectContext executeFetchRequest:request error:&error]mutableCopy];
    if (mutableFetch == nil) {
        NSLog(@"Error: %@,%@",error,[error userInfo]);
    }
    self.users = mutableFetch;
    NSLog(@"the count of users:%lu",(unsigned long)self.users.count);
    for (Users *user in self.users) {
        if ([self.username.text isEqualToString:user.user_name]) {
            if ([self.password.text isEqualToString:user.user_password]) {
                self.query = YES;
                break;
            }
        }        NSLog(@"--name:%@---password:%@--",user.user_name,user.user_password);
    }
    if (!self.query) {
        [self showAlert:@"用户名或密码错误,请重新输入"];
    }

}
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    [self.username resignFirstResponder];
    [self.password resignFirstResponder];
}
-(void)showAlert:(NSString*)infomation{
    UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"提示:" message:infomation delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
    [alert show];
}
@end

　　

效果如图所示：

点击Add按钮会输出:Save successful     点击query会输出如下图所示：

之所以有五条数据是因为之前添加了四条数据，已经保存在CoreDataTwo.sqlite数据库中

附上源码