LINQ动态查询库 [英] LINQ Dynamic Query Library

问题描述

我建立与实体框架4.一个ASP.Net MVC 3应用程序当code两片下面执行时，这两个变量（QUERY1和QUERY2）有一个返回类型

I am building an ASP.Net MVC 3 application with Entity Framework 4. When the two pieces of code below are executed, both variables (query1 and query2) have a return type of

System.Data.Objects.ObjectQuery<Asset.Model.Equipment>

查询1使用的ObjectContext的直接实例，但是，QUERY2使用存储库模式，也就是说，它在EquipmentService，这反过来调用设备库名称相同的方法调用GetEquipment。无论是在服务和回报库方法

Query1 uses a direct instance of the ObjectContext, however, Query2 uses a repository pattern, ie, it calls GetEquipment in EquipmentService, which in turns calls the same named method in Equipment Repository. Both the methods in the Service and Repository return

IQueryable<Equipment>

怎么样，这里是我的问题，怎么就QUERY2只会工作，当我包括

How, here's my question, how come query2 will only work when I include

using System.Linq.Dynamic;

在我的控制器顶部

At the top of my controller

using (AssetEntities context = new AssetEntities())
        {
            var query1 = context.Equipments
            .OrderBy("it." + sidx + " " + sord)
            .Skip(pageIndex * pageSize)
            .Take(pageSize);
        }


        var query2 = equipService.GetEquipment()
            .OrderBy(sidx + " " + sord)
            .Skip(pageIndex * pageSize)
            .Take(pageSize);

如果我从我的控制器omitt System.Linq.Dynamic，我得到内​​QUERY2一个错误在

If I omitt System.Linq.Dynamic from my controller, I get an error within Query2 at

.OrderBy(sidx + " " + sord)

其中规定

The type arguments for method 'System.Linq.Queryable.OrderBy<TSource,TKey>(System.Linq.IQueryable<TSource>, System.Linq.Expressions.Expression<System.Func<TSource,TKey>>)' cannot be inferred from the usage. Try specifying the type arguments explicitly

有谁知道为什么QUERY1可以不必使用System.Linq.Dynamic工作，但需要QUERY2它来执行？

Does anyone know why query1 can work without having to use System.Linq.Dynamic, but that query2 needs it to execute?

谢谢大家。

推荐答案

在第一个查询 context.Equipments 的类型的ObjectQuery＆LT;设备＆GT; 。在的ObjectQuery＆LT; T＆GT; 有方法的的OrderBy（串）其中一个需要 .OrderBy（吧。+ SIDX ++ SORD）。所以第一个查询的工作。

In the first query context.Equipments has type ObjectQuery<Equipment>. The ObjectQuery<T> has the method OrderBy(string) which one need for .OrderBy("it." + sidx + " " + sord). So the first query work.

在你使用 equipService.GetEquipment（）类型的第二个查询的IQueryable＆LT;设备＆GT; 。在的IQueryable＆LT; T＆GT; 只有扩展方法的排序依据与防爆pression＆LT; Func键＆LT; T，TKEY的＆GT;＆GT; 作为参数，而不是字符串。因此，要使用排序依据与的IQueryable＆LT;设备＆GT; 你必须写像

In the second query you use equipService.GetEquipment() of the type IQueryable<Equipment>. The IQueryable<T> has only extension method OrderBy with Expression<Func<T, TKey>> as the parameter instead of string. So to use OrderBy with IQueryable<Equipment> you have to write something like

equipService.GetEquipment().OrderBy(e => e.equipmentID)

但它不是你可以使用的东西。为了你需要另一个分机方法，它可以为您提供LINQ动态查询库中的形式 System.Linq.Dynamic 。

在很多情况下，LINQ到实体拥有诸多限制的，但在你的情况下，它有更多的优点的LINQ to SQL。所以，我建议你留在LINQ到实体在您的案件。我相信，在路上你会收到，因为直接在您使用实体框架的原生支持所有功能更​​好的性能。

In many cases LINQ to Entities has many restrictions, but in your case it has more advantages as LINQ to SQL. So I recommend you to stay by LINQ to Entities in your case. I am sure that in the way you will receive better performance because of native support of all function directly in the Entity Framework which you use.

由于LINQ到实体或的ObjectQuery＆LT;设备＆GT; 支持其中（串）方法（以完全相同<一个HREF =htt​​p://msdn.microsoft.com/en-us/library/bb338811.aspx相对=nofollow> ObjectQuery.Where（字符串predicate，则params ObjectParameter []参数）方法），你可以比较容易实现过滤/在jqGrid的搜索。 。凡的用法可能是

Because LINQ to Entities or ObjectQuery<Equipment> supports Where(string) method (to be exactly ObjectQuery.Where(string predicate, params ObjectParameter[] parameters) method) you can relatively easy implement filtering/searching in jqGrid. The usage of .Where can be

.Where("it.equipmentID < 100")

或

.Where("it.equipmentID < @maxId", new ObjectParameter ("maxId", 100))

例如（maxId的用法，而不是@maxId中的 ObjectParameter 不是打字错误）。

for example (the usage of "maxId" instead of "@maxId" in the ObjectParameter is not typing error).

更新时间：：的the回答你可以找到 足见例如如何实现过滤/搜索在jqGrid的基础上，我上面描述的想法。

UPDATED: In "UPDATED" part of the answer you can find the example which shows how to implement filtering/searching in jqGrid based on the idea which I described above.

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