web api 2 学习笔记 (OData Batch request)

之前介绍过OData 中实现RPC的写法，今天在来一个批量操作。

参考 : https://damienbod.wordpress.com/2014/08/14/web-api-odata-v4-batching-part-10/

http://www.odata.org/getting-started/advanced-tutorial/

public static void Register(HttpConfiguration config)
{
    DefaultODataBatchHandler odataBatchHandler = new DefaultODataBatchHandler(GlobalConfiguration.DefaultServer);
    odataBatchHandler.MessageQuotas.MaxOperationsPerChangeset = 10;
    odataBatchHandler.MessageQuotas.MaxPartsPerBatch = 10;
    config.MapODataServiceRoute("odata", "api", GetModel(), odataBatchHandler);           
}

填入DefaultODataBatchHandler就可以了.

前端js

var xhr = new XMLHttpRequest();
xhr.open("POST", "http://localhost:4274/api/$batch", true);
xhr.setRequestHeader("Content-Type", "multipart/mixed; boundary=batch_ebdc0b88-eeb1-4dd6-b170-74331f39bd03");
xhr.setRequestHeader("OData-Version", "4.0");
xhr.setRequestHeader("singleTransaction", "true");

var body = [];
//POST
body.push('--batch_ebdc0b88-eeb1-4dd6-b170-74331f39bd03');
body.push('Content-Type: multipart/mixed; boundary=changeset_54ac09ec-f437-4b08-9925-fd42ed7bd58f');
body.push('');
body.push('--changeset_54ac09ec-f437-4b08-9925-fd42ed7bd58f');
body.push('Content-Type: application/http');
body.push('Content-Transfer-Encoding: binary');
body.push('Content-ID: 1');
body.push('');
body.push('POST http://localhost:4274/api/products HTTP/1.1');
body.push('OData-Version: 4.0');
body.push('Content-Type: application/json;odata.metadata=minimal');
body.push('Accept: application/json;odata.metadata=minimal');
body.push('');
body.push('{"code":"mk100"}');
body.push('--changeset_54ac09ec-f437-4b08-9925-fd42ed7bd58f--');

//PUT
body.push('--batch_ebdc0b88-eeb1-4dd6-b170-74331f39bd03');
body.push('Content-Type: multipart/mixed; boundary=changeset_2346da5e-88c9-4aa5-a837-5db7e1368147');
body.push('');
body.push('--changeset_2346da5e-88c9-4aa5-a837-5db7e1368147');
body.push('Content-Type: application/http');
body.push('Content-Transfer-Encoding: binary');
body.push('Content-ID: 2');
body.push('');
body.push('PUT http://localhost:4274/api/products(1) HTTP/1.1');
body.push('OData-Version: 4.0');
body.push('Content-Type: application/json;odata.metadata=minimal');
body.push('Accept: application/json;odata.metadata=minimal');
body.push('');
body.push('{"id":1,"code":"mk100"}');
body.push('--changeset_2346da5e-88c9-4aa5-a837-5db7e1368147--');


//DELETE
body.push('--batch_ebdc0b88-eeb1-4dd6-b170-74331f39bd03');
body.push('Content-Type: multipart/mixed; boundary=changeset_2346da5e-88c9-4aa5-a837-5db7e1368142');
body.push('');
body.push('--changeset_2346da5e-88c9-4aa5-a837-5db7e1368142');
body.push('Content-Type: application/http');
body.push('Content-Transfer-Encoding: binary');
body.push('Content-ID: 3');
body.push('');
body.push('DELETE http://localhost:4274/api/products(1) HTTP/1.1');
body.push('OData-Version: 4.0');
body.push('Content-Type: application/json;odata.metadata=minimal');
body.push('Accept: application/json;odata.metadata=minimal');
body.push('');
body.push('--changeset_2346da5e-88c9-4aa5-a837-5db7e1368142--');
            
//GET
body.push('--batch_ebdc0b88-eeb1-4dd6-b170-74331f39bd03');
body.push('Content-Type: application/http');
body.push('Content-Transfer-Encoding: binary');
body.push('Content-ID: 4');
body.push('');
body.push('GET http://localhost:4274/api/products HTTP/1.1');
body.push('OData-Version: 4.0');
body.push('Content-Type: application/json;odata.metadata=minimal');
body.push('Accept: application/json;odata.metadata=minimal');
body.push('');

body.push('--batch_ebdc0b88-eeb1-4dd6-b170-74331f39bd03--');
body.push('');
var data = body.join("
");
xhr.send(data);

从上面代码可以看出，我们所有的请求需要通过一个大请求来包装，把所有的小请求用string写进大请求的body就可以了。

需要特别注意的事string的格式，连空行都是非常重要的哦！

参考 http://www.odata.org/documentation/odata-version-3-0/batch-processing/

虽然这是v3的但是可以看一下, 2.2 Batch Request Body 

请求分2中，一种叫changeset，一种叫 operation 

changeset 是指那些会改变资源的请求(e.g. POST,PUT,DELETE,ACTION)， operation 是指不会改变资源的请求 (e.g. GET,FUNCTION) 

代码中可以看出来，这2种写法会有不同。

通常我们在做批量操作时希望会有transaction

这时我们可以扩展 DefaulODataBatchHandle 

public class ODataBatchHandlerSingleTransaction : DefaultODataBatchHandler
{
    public ODataBatchHandlerSingleTransaction(HttpServer httpServer)
        : base(httpServer)
    {
    }

    public async override Task<IList<ODataBatchResponseItem>> ExecuteRequestMessagesAsync(IEnumerable<ODataBatchRequestItem> requests,CancellationToken cancellation)
    {
        if (requests == null) { throw new ArgumentNullException("requests"); }            
        IList<ODataBatchResponseItem> responses = new List<ODataBatchResponseItem>();
                         
        try
        {
            using (DB db = new DB())
            {
                using (DbContextTransaction trans = db.Database.BeginTransaction())
                {
                    foreach (ODataBatchRequestItem request in requests)
                    {
                        var changeSetResponse = (ChangeSetResponseItem)await request.SendRequestAsync(Invoker, cancellation);
                        responses.Add(changeSetResponse);
                    }
                    bool isAllOk = responses.All(response => ((ChangeSetResponseItem)(response)).Responses.All(r => r.IsSuccessStatusCode));
                    if (isAllOk)
                    {
                        trans.Commit();
                    }
                    else
                    {
                        trans.Rollback();
                    }
                }
            }
        }
        catch
        {
            foreach (ODataBatchResponseItem response in responses)
            {
                if (response != null)
                {
                    response.Dispose();
                }
            }
            throw;
        }
        return responses;
    }      
} 

拦截以后我们就可以在这一层创建 database Context 和 transaction ， controller 内就可以通过任何方式来获取到这里的 context 来做使用. 

比如可以使用 Request.Items 来保存传值. (注 : httpRequest 和 httpRequestMessage 是不同的，我们在controller使用的是 message 哦)  

还有一点要特别注意的是，如果你需要transaction就不应该有请求，因为GET 请求会在 ExecuteRequestMessagesAsync 之后才执行，如果这时我们释放掉了 database context 那么就会有问题了.