CoreData使用

1.如果想创建一个带有coreData的程序,要在项目初始化的时候勾选中

2.创建完成之后,会发现在AppDelegate里多出了几个属性,和2个方法 

<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>

managedObjectContext （被管理的数据上下文）操作实际内容（操作持久层）作用：插入数据，查询数据，删除数据

 

NSManagedObjectModel（被管理的数据模型）数据库所有表格或数据结构，包含各实体的定义信息 作用：添加实体的属性，建立属性之间的关系操作方法：视图编辑器，或代码

NSPersistentStoreCoordinator（持久化存储助理）相当于数据库的连接器 作用：设置数据存储的名字，位置，存储方式，和存储时机

方法saveContext表示：保存数据到持久层（数据库）

方法applicationDocumentsDirectory表示：应用程序沙箱下的Documents目录路径

3.如果想创建一个实体对象的话,需要点击.xcdatamodel,Add Entity,添加想要的字段

4.生成对象文件,command+n,然后选中CoreData里的NSManagerObjectSubClass进行关联,选中实体创建

5.添加数据 

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（实体结构）相当于表格结构

6.取出数据查询 

/* 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.删除数据 

/* 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 

    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;

    //  注意 ascending:YES 属性决定排序顺序