多条件动态LINQ 组合查询

 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);

                }

            }