动态拼接LINQ 查询条件

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);

 

                }

 

            }