多条件动态LINQ 组合查询

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。

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);

}

}