动态拼接LINQ 查询条件

最新推荐文章于 2025-05-10 13:32:49 发布

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本文展示了如何使用LINQ查询和Lambda表达式进行条件筛选，通过具体的代码实例介绍了如何根据不同的参数灵活地构建查询条件。

以往我们都是通过判断的方式来拼接查询的SQL字符串，但是现在我们面对是强类型的LINQ查询，是否可以很方便的进行类似查询。

eg:

string _UserID = string.Empty;
           _UserID = "E351D301-F64B-412C-B9EF-573F41235AF2";
 
           string _UserName = string.Empty;
           _UserName = "admin";
 
           string _employyName = string.Empty;
           _employyName = "测试1";
 
           using (var xj = new XJGasBottles_testDataContext())
           {
               //Linq写法
               var usersLinq = from us in xj.Users
                               where (string.IsNullOrEmpty(_UserID) || us.UserID.ToString() == _UserID)
                                      && (string.IsNullOrEmpty(_UserName) || us.UserName == _UserName)
                                      || (us.EmpName == _employyName)
                               //where string.IsNullOrEmpty(_UserID) || us.UserID.ToString()==_UserID
                               //where string.IsNullOrEmpty(_UserName) || us.UserName==_UserName
                               select us;
               foreach (var item in usersLinq)
               {
                   Console.WriteLine("Linq:");
                   Console.WriteLine(item.UserID + "_" + item.UserName);
 
               }
 
               //Lamda写法
               var usersLamda = xj.Users.Where(s => (string.IsNullOrEmpty(_UserID) || s.UserID.ToString() == _UserID) &&
                                               (string.IsNullOrEmpty(_UserName) || s.UserName == _UserName) ||
                                               (s.EmpName==_employyName)
                                         )
                                   .Select(s => s);
 
               foreach (var item in usersLamda)
               {
                   Console.WriteLine("Lamda:");
                   Console.WriteLine(item.UserID + "_" + item.UserName);
 
               }
 
           }