多條件動態LINQ 組合查詢

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

參考：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

 

以往我們都是通過判斷的方式來拼接查詢的SQL字符串，但是現在我們面對是強類型的LINQ查詢，是否可以很方便的進行類似查詢。

 

eg:

 string _UserID = string.Empty;
            _UserID = "E351D301-F64B-412C-B9EF-573F41235AF2";

            string _UserName = string.Empty;
            _UserName = "admin";

            string _employyName = string.Empty;
            _employyName = "測試1";

            using (var xj = new XJGasBottles_testDataContext())
            {
                //Linq寫法
                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寫法
                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);

                }

            }