有没有使用LINQ动态创建一个过滤器的模式？ [英] Is there a pattern using Linq to dynamically create a filter?

问题描述

有没有使用LINQ动态创建一个过滤器的模式？

Is there a pattern using Linq to dynamically create a filter?

我需要创建自定义筛选名单上，在过去，我只想动态创建SQL ...这似乎不像这是可能使用LINQ。

I have the need to create custom filtering on a list, in the past I would just dynamically create the SQL...it doesn't seem like this is possible with Linq.

推荐答案

退房的<一个href="http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx">Dynamic LINQ的图书馆从ScottGu的博客：

例如，下面是一个标准的类型安全的LINQ to SQL VB查询检索数据从Northwind数据库，并在ASP.NET GridView控件中显示出来：

For example, below is a standard type-safe LINQ to SQL VB query that retrieves data from a Northwind database and displays it in a ASP.NET GridView control:

Dim Northwind As New NorthwindDataContext
Dim query = From q In Northwind.Products Where p.CategoryID = 2 And p.UnitPrice > 3 Order By p.SupplierID Select p

Gridview1.DataSource = query
GridView1.DataBind()

使用LINQ DynamicQuery库，我可以重新写上面的查询EX pression，而不是像这样

Using the LINQ DynamicQuery library I could re-write the above query expression instead like so

Dim Northwind As New NorthwindDataContext
Dim query = Northwind.Products .where("CategoryID=2 And UnitPrice>3") . OrderBy("SupplierId")
Gridview1.DataSource = query
GridView1.DataBind()

请注意条件，where子句和排序，排序依据子句现在采取的字符串前pressions代替code EX pressions。因为它们是后期绑定字符串，我可以动态地构建它们。例如：我可以用我的应用程序，使他们能够构造查询自己（包括任意的条件子句）提供用户界面，最终用户业务分析师。

Notice how the conditional-where clause and sort-orderby clause now take string expressions instead of code expressions. Because they are late-bound strings I can dynamically construct them. For example: I could provide UI to an end-user business analyst using my application that enables them to construct queries on their own (including arbitrary conditional clauses).

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