blocks|key|2881038|text|来自URL的查询被翻译成一个LINQ表达式树，然后根据您的操作返回的IQueryable执行。您可以分析表达式并以任何您想要的方式提供结果。缺点是您需要实现IQueryable，这并不是非常容易。如果你感兴趣，可以看看这篇博文系列：http://blogs.msdn.com/b/vitek/archive/2010/02/25/data-services-expressions-part-1-intro.aspx。它谈到了WCF数据服务，但Web+API使用的筛选器表达式将非常相似。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2881039|entityMap|0|LINK|mutability|MUTABLE|url|http://blogs.msdn.com/b/vitek/archive/2010/02/25/data-services-expressions-part-1-intro.aspx^0|38|2K|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

The query from the URL gets translated into a LINQ expression tree which is then executed against the IQueryable your operation returns. You can analyze the expression and provide the results in any way you want. The downside is that you need to implement IQueryable which is not super easy. Take a look at this blog post series if you're interested: <a href="http://blogs.msdn.com/b/vitek/archive/2010/02/25/data-services-expressions-part-1-intro.aspx" rel="nofollow">http://blogs.msdn.com/b/vitek/archive/2010/02/25/data-services-expressions-part-1-intro.aspx</a>. It talks about WCF Data Services, but the filter expressions used by the Web API will be very similar.

blocks|key|227082|text|使用Web-api的一种方法是使用客户消息处理程序http://www.asp.net/web-api/overview/working-with-http/http-message-handlers|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|227083|编写一个自定义处理程序，如下所示：|style|BOLD|227084|public+class+CustomHandler+:+DelegatingHandler
++++{
++++++++protected+override+Task<HttpResponseMessage>+SendAsync(
++++++++++++HttpRequestMessage+request,+CancellationToken+cancellationToken)
++++++++{
++++++++++++return+base.SendAsync(request,+cancellationToken).ContinueWith(
++++++++++++++++(task)+=>
++++++++++++++++{
++++++++++++++++++++HttpResponseMessage+response+=+task.Result;
++++++++++++++++++++var+persons+=+response.Content.ReadAsAsync<IQueryable<Person>>().Result;
++++++++++++++++++++var+persons2+=+new+List<Person>();+//This+can+be+the+modified+model+completely+different
++++++++++++++++++++foreach+(var+item+in+persons)
++++++++++++++++++++{
++++++++++++++++++++++++item.Name+=+"changed";+//+here+you+can+change+the+data
++++++++++++++++++++++++//persons2.Add(....);+//Depending+on+the+results+modify+this+custom+model
++++++++++++++++++++}
++++++++++++++++++++//overwrite+the+response
++++++++++++++++++++response+=+new+HttpResponseMessage<IEnumerable<Person>>(persons2);+
++++++++++++++++++++return+response;
++++++++++++++++}
++++++++++++);
++++++++}
++++}|code-block|syntax|javascript|227085|global.asax.cs中的注册|227086|应用程序类中的方法：|227087|static+void+Configure(HttpConfiguration+config)
+{
+++++config.MessageHandlers.Add(new+CustomHandler());+
+}

protected+void+Application_Start()
{
+++++....
+++++.....
+++++//call+the+configure+method
+++++Configure(GlobalConfiguration.Configuration);
+}|227088|entityMap|0|LINK|mutability|MUTABLE|url|http://www.asp.net/web-api/overview/working-with-http/http-message-handlers^0|P|23|0|0|0|H|0|0|G|2|0|0|A|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|6|7|14|8|@$A|15|B|16|F|G]]|9|@]|C|$]]|$1|H|3|I|5|J|7|17|8|@]|9|@]|C|$K|L]]|$1|M|3|N|5|6|7|18|8|@$A|19|B|1A|F|G]]|9|@]|C|$]]|$1|O|3|P|5|6|7|1B|8|@$A|1C|B|1D|F|G]]|9|@]|C|$]]|$1|Q|3|R|5|J|7|1E|8|@]|9|@]|C|$K|L]]|$1|S|3|-4|5|6|7|1F|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]]]

One way With Web-api would be with customer message handler <a href="http://www.asp.net/web-api/overview/working-with-http/http-message-handlers" rel="nofollow">http://www.asp.net/web-api/overview/working-with-http/http-message-handlers</a>

Write a custom handler like below:

<pre><code>public class CustomHandler : DelegatingHandler
 {
 protected override Task&lt;HttpResponseMessage&gt; SendAsync(
 HttpRequestMessage request, CancellationToken cancellationToken)
 {
 return base.SendAsync(request, cancellationToken).ContinueWith(
 (task) =&gt;
 {
 HttpResponseMessage response = task.Result;
 var persons = response.Content.ReadAsAsync&lt;IQueryable&lt;Person&gt;&gt;().Result;
 var persons2 = new List&lt;Person&gt;(); //This can be the modified model completely different
 foreach (var item in persons)
 {
 item.Name = "changed"; // here you can change the data
 //persons2.Add(....); //Depending on the results modify this custom model
 }
 //overwrite the response
 response = new HttpResponseMessage&lt;IEnumerable&lt;Person&gt;&gt;(persons2); 
 return response;
 }
 );
 }
 }
</code></pre>

Register in global.asax.cs

Method in application class: 

<pre><code>static void Configure(HttpConfiguration config)
 {
 config.MessageHandlers.Add(new CustomHandler()); 
 }

protected void Application_Start()
{
 ....
 .....
 //call the configure method
 Configure(GlobalConfiguration.Configuration);
 }
</code></pre>

blocks|key|3095081|text|我用WCF+Data+Services和asp.net+MVC3.5做了类似的事情，但它有点杂乱无章。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3095082|第一步是重写路径，以便跳过和顶部选项不会应用两次，一次由您应用，一次由运行时应用。|3095083|我用HttpModule进行了重写。在你的BeginRequest方法中，你会有这样的代码：|3095084|HttpApplication+app+=+(HttpApplication)sender;
if+(HttpContext.Current.Request.Path.Contains(YOUR_SVC))
{
++++if+(app.Request.Url.Query.Length+>+0)
++++{
++++++++//skip+questionmark
++++++++string+queryString+=+app.Request.Url.Query.Substring(1)+
++++++++++++++++++++.Replace("$filter=",+"filter=")
++++++++++++++++++++.Replace("$orderby=",+"orderby=")
++++++++++++++++++++.Replace("$top=",+"top=")
++++++++++++++++++++.Replace("$skip=",+"skip=");

++++++++++++++++HttpContext.Current.RewritePath(app.Request.Path,+"",+queryString);
++++}
}|code-block|syntax|javascript|3095085|然后，只需检查查询字符串并提取所需的参数。|3095086|if+(HttpContext.Current.Request.QueryString["filter"]+!=+null)
++++var+filter+=+HttpContext.Current.Request.QueryString["filter"]+as+string;|3095087|然后拆分过滤器字符串，并将其解析为sql语句或任何其他db命令。在我的案例中我使用的是NHibernate。我还能够限制我支持的过滤器命令，这使得事情变得更容易。例如，我没有进行分组。主要是比较运算符。|3095088|在OData.org上有一个过滤器操作符的列表。用"+and“和"or”将字符串拆分成单独的子句。用一个空格拆分每个子句，您应该得到一个3元素数组，其中属性名称在运算符1中，值在2中。|offset|length|3095089|这些子句是针对一个人的，但我假设你能够将它们转换成能从数据库中提取正确结果的东西。|3095090|我最终放弃了这种方法，因为它不适用于帖子。我必须编写自己的Linq提供程序，但编写自己的过滤器字符串解析器更容易理解。|3095091|entityMap|0|LINK|mutability|MUTABLE|url|http://www.odata.org/documentation/uri-conventions#FilterSystemQueryOption^0|0|0|0|0|0|0|0|1|9|0|0|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|17|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|18|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|19|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|1A|8|@]|9|@]|A|$]]|$1|M|3|N|5|H|7|1B|8|@]|9|@]|A|$I|J]]|$1|O|3|P|5|6|7|1C|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1D|8|@]|9|@$S|1E|T|1F|1|1G]]|A|$]]|$1|U|3|V|5|6|7|1H|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1I|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1J|8|@]|9|@]|A|$]]]|Z|$10|$5|11|12|13|A|$14|15]]]]

I did something like this with WCF Data Services and asp.net mvc 3.5 but it was a bit of a kludge. 

The first step is to rewrite the path so that the skip and top options don't get applied twice, once by you and once by the runtime. 

I did the rewriting with an HttpModule. In your BeginRequest method you'd have code like this:

<pre><code>HttpApplication app = (HttpApplication)sender;
if (HttpContext.Current.Request.Path.Contains(YOUR_SVC))
{
 if (app.Request.Url.Query.Length &gt; 0)
 {
 //skip questionmark
 string queryString = app.Request.Url.Query.Substring(1) 
 .Replace("$filter=", "filter=")
 .Replace("$orderby=", "orderby=")
 .Replace("$top=", "top=")
 .Replace("$skip=", "skip=");

 HttpContext.Current.RewritePath(app.Request.Path, "", queryString);
 }
}
</code></pre>

Then just examine the query string and pluck out the parameters you need. 

<pre><code>if (HttpContext.Current.Request.QueryString["filter"] != null)
 var filter = HttpContext.Current.Request.QueryString["filter"] as string;
</code></pre>

Then split the filter string and parse it into a sql statement or any other db commands. I was using NHibernate in my case. I was also able to limit what filter commands I supported which made things easier. I didn't do groupings for example. Mostly just the comparison operators.

There's a list of filter operators at <a href="http://www.odata.org/documentation/uri-conventions#FilterSystemQueryOption" rel="nofollow">OData.org</a>. Split the string by "and" and "or" into individual clauses. Split each clause by a space and you should get a 3 element array with the property name in [0] the operator in [1] and the value in [2].

The clauses will be in terms of a Person but I'm assuming you'll be able to convert them into something that will pull the right results out of the db. 

I ended up abandoning this approach since it won't work for POSTS. I had to write my own Linq provider but writing my own filter string parser made that easier to understand.

blocks|key|223738|text|我只是偶然发现了这篇旧文章，我添加了这个答案，因为现在自己处理OData查询非常容易。下面是一个例子：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|223739|[HttpGet]
[ActionName("Example")]
public+IEnumerable<Poco>+GetExample(ODataQueryOptions<Poco>+queryOptions)
{
++++var+data+=+new+Poco[]+{+
++++++++new+Poco()+{+id+=+1,+name+=+"one",+type+=+"a"+},
++++++++new+Poco()+{+id+=+2,+name+=+"two",+type+=+"b"+},
++++++++new+Poco()+{+id+=+3,+name+=+"three",+type+=+"c"+}
++++};

++++var+t+=+new+ODataValidationSettings()+{+MaxTop+=+2+};
++++queryOptions.Validate(t);

++++//this+is+the+method+to+filter+using+the+OData+framework
++++//var+s+=+new+ODataQuerySettings()+{+PageSize+=+1+};
++++//var+results+=+queryOptions.ApplyTo(data.AsQueryable(),+s)+as+IEnumerable<Poco>;

++++//or+DIY
++++var+results+=+data;
++++if+(queryOptions.Skip+!=+null)+
++++++++results+=+results.Skip(queryOptions.Skip.Value);
++++if+(queryOptions.Top+!=+null)
++++++++results+=+results.Take(queryOptions.Top.Value);

++++return+results;
}

public+class+Poco
{
++++public+int+id+{+get;+set;+}
++++public+string+name+{+get;+set;+}
++++public+string+type+{+get;+set;+}
}|code-block|syntax|javascript|223740|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I just stumbled across this old post and I'm adding this answer as it's now very easy to handle the OData queries yourself. Here's an example:

<pre><code>[HttpGet]
[ActionName("Example")]
public IEnumerable&lt;Poco&gt; GetExample(ODataQueryOptions&lt;Poco&gt; queryOptions)
{
 var data = new Poco[] { 
 new Poco() { id = 1, name = "one", type = "a" },
 new Poco() { id = 2, name = "two", type = "b" },
 new Poco() { id = 3, name = "three", type = "c" }
 };

 var t = new ODataValidationSettings() { MaxTop = 2 };
 queryOptions.Validate(t);

 //this is the method to filter using the OData framework
 //var s = new ODataQuerySettings() { PageSize = 1 };
 //var results = queryOptions.ApplyTo(data.AsQueryable(), s) as IEnumerable&lt;Poco&gt;;

 //or DIY
 var results = data;
 if (queryOptions.Skip != null) 
 results = results.Skip(queryOptions.Skip.Value);
 if (queryOptions.Top != null)
 results = results.Take(queryOptions.Top.Value);

 return results;
}

public class Poco
{
 public int id { get; set; }
 public string name { get; set; }
 public string type { get; set; }
}
</code></pre>

I have a Web Service made using the WebAPI provided by ASP .NET MVC 4.
I know that the layer on top of which WebAPI works automatically handles OData Queries (such as <code>$filter</code>, <code>$top</code>, <code>$skip</code>), but what if I want to handle the filtering by myself?

<a href="https://i.stack.imgur.com/Bgv8W.jpg" rel="noreferrer">I don't simply return data from my database</a>, but I have another layer which adds some properties, makes some conversions etc. So querying ALL of my data, converting them and returning them to the WebAPI class for OData filtering isn't just good enough. It's of course terribly slow, and generally a crappy idea.

So is there a way to propagate the OData query parameters from my WebAPI entry point to the functions I call to get and convert the data?

For example, a GET to <code>/api/people?$skip=10&amp;$top=10</code> would call on the server:

<pre><code>public IQueryable&lt;Person&gt; get() {
 return PersonService.get(SomethingAboutCurrentRequest.CurrentOData);
}
</code></pre>

And in <code>PersonService</code>:

<pre><code>public IQueryable&lt;Person&gt; getPeople(var ODataQueries) {
 IQueryable&lt;ServerSidePerson&gt; serverPeople = from p in dbContext.ServerSidePerson select p;
 // Make the OData queries
 // Skip
 serverPeople = serverPeople.Skip(ODataQueries.Skip);
 // Take
 serverPeople = serverPeople.Take(ODataQueries.Take);
 // And so on
 // ...

 // Then, convert them
 IQueryable&lt;Person&gt; people = Converter.convertPersonList(serverPeople);
 return people;
}
</code></pre>

ASP .NET MVC 4 WebApi: Manually handle OData queries

数据库

服务器

我有一个使用ASPMVC4提供的 WebAPI 创建的Web服务。我知道WebAPI工作在其上的层会自动处理OData查询(如$filter、$top、$skip)，但如果我想自己处理过滤怎么办？，但我有另一个层，它添加了一些属性，进行了一些转换等。所以查询我的所有数据，转换它们，并将它们返回到WebAPI类以进行OD...

问ASP .NET MVC 4 WebApi:手动处理OData查询
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