Linq表达词典 [英] Dictionary of Linq Expression

问题描述

可能重复：

在T中声明func< Out结果>动态地

我正在使用linq-to-sql来构建一个查询为了提供排序功能，我写了这样一个例子：

I'm trying to build a query using linq-to-sql and, in order to provide sorting capabilities, I wrote something like this:

private Dictionary<string, Expression<Func<DataAccess.Auditing, object>>> OrderDict { get; set; }


OrderDict = new Dictionary<string,Expression<Func<Augeos.GereonWeb.DataAccess.Auditing, object>>>();
OrderDict.Add("Date", p => (DateTime)p.RequestDateTime);
OrderDict.Add("Username", p => (string)p.CdUsername);
OrderDict.Add("Portfolio", p => (string)p.CdPortfolio);
OrderDict.Add("Url", p => (string)p.RequestedUrl);
OrderDict.Add("Result", p => (bool)p.RequestResult);
OrderDict.Add("Duration", p => (float)p.RequestDuration);


private IQueryable<DataAccess.Auditing> SetOrder(string orderBy, bool orderDirection, IQueryable<DataAccess.Auditing> query)
{
    if (orderDirection)
    return query.OrderByDescending(OrderDict[orderBy]);
    else
    return query.OrderBy(OrderDict[orderBy]);
}

我的目标是使用SortOrder函数对查询进行排序。主要的问题是Func返回一个对象，而linq不能排序这个类型的元素。我真的需要使用对象作为返回类型，因为我必须按各种类型排序。实际上是否可以稍微修改此代码并使其正常工作？

My goal is to use the SortOrder function to sort the query. The main problem is that Func returns an object and linq cannot sort elements of this type. I truly need to use object as a return type because I have to sort by a wide range of types. Is it actually possible to slightly modify this code and make it to work?

谢谢，

Gio

推荐答案

如果你在查询的表达式树中必须要非常低级才能做这样的事情。一个更简单的方法是使用DynamicLinq库，您可以在其中执行.OrderBy（），其中列为字符串值。可以找到文档这里是Scott Guthrie的博客。

Hm you'd have to go very low-level in the expression tree of your query to do such a thing. A much easier way would be to use the DynamicLinq library, where you can do .OrderBy() with a column as string value. Documentation can be found here on Scott Guthrie's blog.

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