LINQ TO SQL如何实现动态查询？？？

梦在旅途 2014-08-27 01:11:29

LINQ TO SQL如何实现动态查询，也就是类似SQL查询拼接的模式！
之所以想实现在这样功能，主要是考虑到多条件查询，查询的字段及内容都不是确定的，
哪位高手有做过，还请指教，谢谢！

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宝_爸 2014-08-28

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有库的 System.Linq.Dynamic Project Description Extends System.Linq.Dynamic to support Execution of Lambda expressions defined in a string against Entity Framework or any provider that supports IQueryable. I originally came across this source code on Scott Guthrie's Blog while searching for a mechanism to execute dynamic linq statements against entity framework. While this code partially fulfilled my need both it and the assembly System.Linq.Dynamic.dll available for download from NuGet lacked the exact functionality I required. Specifically it did not allow me to execute a full lambda expression represented as a string against my entity objects. In addition it lacked support for Take and Union as well as many other extension functions, though these were the only two with which I was interested. As a consequence I extended the code to support these features. I thought my efforts might benefit someone else so I have decided to host it on codeplex. The original code is licensed under Ms-PL and in accordance with this license the derived codebase I have created is licensed similarly. http://dynamiclinq.codeplex.com/

effun 2014-08-28

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public Person[] QueryPersons(string name, int? gender)
{
  MyDataContext dc = new MyDataContext();
  IQueryable<Person> q = dc.Persons;

  if (!String.IsNullOrEmpty(name))
    q = q.Where(person => person.Name.Contains(name));

 if (gender.HasValue)
    q = q.Where(person => person.Gender = gender);

  return q.OrderBy(person => person.Name).ToArray();
}

threenewbee 2014-08-27

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google dynamic linq 使用这个库，可以把查询写成类似sql那样的字符串，以及得到dynamic结果的查询。

以专业开发人员为伍 2014-08-27

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引用楼主 wheeky 的回复:

LINQ TO SQL如何实现动态查询，也就是类似SQL查询拼接的模式！之所以想实现在这样功能，主要是考虑到多条件查询，查询的字段及内容都不是确定的，哪位高手有做过，还请指教，谢谢！

首先，查询是可以“自身跟自身”组合的。毕竟是延迟执行的，而Linq to SQL 和 SQL Server 系统都会分别对查询先进性几十种可能性的分析，最后只取最优化的查询计划去执行。不过最重要地是，你为啥不同时使用 ADO.NET 呢？为什么刚学会用两天什么 Linq to SQL 就不用了 ADO.NET 了呢？真是没有长性啊，学什么都是半途而废。跟那种抱着ADO.NET 不敢去尝试 LINQ Provider的人有什么两样呢？