动态拼接LINQ 查询条件

Posted 2020-08-31 Rookie_lee

本文章转载：http://www.cnblogs.com/wangiqngpei557/archive/2013/02/05/2893096.html

参考：http://dotnet.9sssd.com/entfwk/art/960

 http://www.cnblogs.com/killuakun/archive/2008/08/03/1259389.html

http://www.cnblogs.com/snowdream/archive/2008/07/18/1246308.html

 

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);                  }              }