在xcode 4.2.1中通过RHManagedObject 和RHManagedObjectContextManager 来简化 CoreData的处理

项目源码下载 ： 在我的资源里面。

RHManagedObjectContextManager 和 RHManagedObject 来自与 https://github.com/chriscdn/RHManagedObject 在项目中加入 CoreData.framework的框架

在项目中 加入 RHManagedObjectContextManager.h 和 RHManagedObjectContextManager.m ，RHManagedObject.h ,RHManagedObject.m 4个文件。
通过 xcode 4.2 新建一个文件，文件类型是 CoreData 下的Data Model 。命名为
test.xcdatamodeld
然后点击 这个 test.xcdatamodeld 文件，在主视图里面 加入一个 Entity ，名字 叫 ：Customer。增加2个 Attribute ：1 ： name ，2 age


点击其他文件，取消选中这个 test.xcdatamodeld 文件
新建一个文件，类型是CoreData下的NSManagedObject subclass

然后界面上会显示 Data Model的名称，这里显示 test。选中这个test，点击next按钮 ，出现这个 test.xcdatamodeld 文件中定义的Entities ，这里显示 Customer.选中这个Customer ,点击next 按钮。然后在选择保存文档的目录。按按钮 create。这样在项目中就会建立 Customer.h 和 Customer.m文件。
修改 Customer.h文件

#import "RHManagedObject.h"
把原来的基类由 NSManagedObject 修改 为 RHManagedObject. @interface Customer : RHManagedObject

修改RHManagedObjectContextManager.h，这只 2个 define值

#define kDatabaseName @"test.sqlite"

#define kModelName @"test"
kDatabaseName指定的是sqlite数据库的名称，可以任意命名，生成后文件保存在Documents目录下

kModelName指的是数据模型的名称，必须和在项目中创建的.xcdatamodeld文件的文件名前缀名称一致.

修改 Customer.m 的源码 ，加入以下代码：

+(NSString *)entityName
{
return @"Customer";
}
// This returns the name of your xcdatamodeld model, without the extension+(NSString *)modelName {    return @"test";  // 这里要放入xcdatamodeld文件名。不需要后缀}

编写数据库 访问功能

//****************** 数据保存 begin

Customer * customer = (Customer *) [Customer newEntity];
customer.name =@"asdfsf";
customer.age = [[ NSNumber alloc] initWithFloat: 13.4f];

[RHManagedObject commit];

//****************** 数据保存 end

-(NSArray * ) allRecords
{
NSLog(@"获取所有记录");
//NSPredicate *predicate = [NSPredicate predicateWithFormat:@"1=1"];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"smount" ascending:YES];
return [[NSArray alloc] initWithArray:[CustomerInfo fetchWithSortDescriptor:sortDescriptor]];

}

官网的例子：

Examples

Once you have setup RHManagedObject it becomes easier to do common tasks. Here are some examples.

Add
a new employee

Employee *employee = [Employee newEntity];
[employee setFirstName:@"John"];
[employee setLastName:@"Doe"];

Fetch
all employees

NSArray *allEmployees = [Employee fetchAll];

Fetch
all employees with first name "John"

NSArray *employees = [Employee fetchWithPredicate:[NSPredicate predicateWithFormat:@"firstName=%@", @"John"]];

Fetch
all employees with first name "John" sorted by last name

NSArray *employees = [Employee fetchWithPredicate:[NSPredicate predicateWithFormat:@"firstName=%@", @"John"] sortDescriptor:[NSSortDescriptor sortDescriptorWithKey:@"lastName" ascending:YES]];

Get
a specific employee record

The

+getWithPredicate:

method will return
the first object if more than one is found.

Employee *employee = [Employee getWithPredicate:[NSPredicate predicateWithFormat:@"employeeID=%i", 12345]];

Count
the total number of employees

NSUInteger employeeCount = [Employee count];

Count
the total number of employees with first name "John"

NSUInteger employeeCount = [Employee countWithPredicate:[NSPredicate predicateWithFormat:@"firstName=%@", @"John"]];

Get
all the unique first names

NSArray *uniqueFirstNames = [Employee distinctValuesWithAttribute:@"firstName" withPredicate:nil];

Get
the average age of all employees

NSNumber *averageAge = [Employee aggregateWithType:RHAggregateAverage key:@"age" predicate:nil defaultValue:nil];

Fire
all employees

[Employee deleteAll];

Fire
a single employee

Employee *employee = [Employee get ...];
[employee delete];

Commit
changes

This must be called in the same thread where the changes to your objects were made.

[Employee commit];

Completely
destroy the Employee model (i.e., delete the .sqlite file)

This is useful to reset your Core Data store after making changes to your model.

[Employee deleteStore];

Get
an object instance in another thread

Core Data doesn't allow managed objects to be passed between threads. However you can generate a new object in a separate thread that's valid for that thread. Here's an example using the

-objectInCurrentThreadContext

method:

Employee *employee = [Employee getWithPredicate:[NSPredicate predicateWithFormat:@"employeID=%i", 12345]];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

// employee is not valid in this thread, so we fetch one that is:
Employee *employee2  = [employee objectInCurrentThreadContext];

// do something with employee2

[Employee commit];});