Question

我正在开发一个iPhone应用程序，它通过json / rest api从服务器检索sqlite数据库。用户可以在本地向其表添加行，并可以在本地更新它。现在，当我向本地数据库中的表添加一些行时，我想从本地更新的数据库中仅将这些新行同步/插入到服务器数据库中。如果有人知道api方法（json / rest）或者如果有任何与之相关的教程，请帮助。

Answer 1

当您说您正在检索“sqlite”数据库时，您是指所有表及其行的“json”表示吗？我假设你实际上并没有发送“sqlite”db文件。

为了通过http发送和检索json，您可以使用NSURLConnection和NSURLRequest来简化，因为它们是内置的。如果要强制映射到核心数据，可以使用RestKit框架进行连接和数据处理。

以下是前一个解决方案的示例实现 - 它假设您是ARC，否则您将需要添加适当的retain和release语句。

1）声明您正在使用的类作为适当的委托

    @interface ClassName : NSObject <NSURLConnectionDelegate>

2）声明将用于接收数据的responseData对象

    //interface
    @property (nonatomic, strong) NSMutableData *responseData;      

    //implementation
    @synthesize responseData;

3）创建发送json请求的函数

    - (void)sendRequest
{
    responseData = [NSMutableData data];

    //whatever your server address is
    NSURL *url = [NSURL URLWithString:@"http://www.resturl.com/whatever"];

    //just sample data - create this dictionary with what you want to send
    NSMutableDictionary *params = [[NSMutableDictionary alloc] init];
    [params setObject:@"SomeValue" forKey:@"SomeKey"];


    NSError *jsonError;
    //NSJSONSerialization is Apple's new json serialization class so we can use it to convert to and from json and foundation objects
    NSData *requestdata = [NSJSONSerialization dataWithJSONObject:params options:0 error:&jsonError];

    NSMutableURLRequest *request;
    request = [NSMutableURLRequest requestWithURL:url];
    [request setHTTPMethod:@"POST"];
    [request setValue:[NSString stringWithFormat:@"%d", [requestdata length]] forHTTPHeaderField:@"Content-Length"];
    [request setValue:@"application/json" forHTTPHeaderField:@"Accept"];
    [request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
    [request setHTTPBody:requestdata];

    //this kicks off the request asynchronously
    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];

    //if you'd rather send a synchronous request, you can use the static NSURLConnection function
    //sendSynchronousRequest:returningResponse:error:
}

4）实现委托函数以接收我们的数据

//any time a piece of data is received we will append it to the responseData object
    - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
    {
        [self.responseData appendData:data];
    }

    //some sort of error, you can print the error or put in some other handling here, possibly even try again but you will risk an infinite loop then unless you impose some sort of limit
    - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
    {
        // Clear the activeDownload property to allow later attempts
        self.responseData = nil;

    }

    //connection has finished, thse requestData object should contain the entirety of the response at this point
    - (void)connectionDidFinishLoading:(NSURLConnection *)connection
    {
        NSError *jsonError;
        NSDictionary *responseDict =
        [NSJSONSerialization JSONObjectWithData:responseData
                                        options:NSJSONWritingPrettyPrinted
                                          error:&jsonError];
        if(responseDict)
        {
            NSLog(@"%@", responseDict);
        }
        else
        {
            NSLog(@"%@", [jsonError description]);
        }

        //clear out our response buffer for future requests
        self.responseData = nil;
    }

如果要使用一些新信息更新远程数据库，只需在本地跟踪新行（而不是仅将它们与完整数据集合并），并将仅包含这些行的新请求发送到将添加的端点他们。这是在不强制实际映射的情况下执行此操作的最简单方法。

如何通过json api更新服务器db上的数据？

1 个答案: