为linq中使用查询字符串的where语句提供默认值

lets first see my codes

让我们先看看我的代码

protected void dsVsl_Selecting(object sender, LinqDataSourceSelectEventArgs e)
{
    string query;
    if (Request.QueryString["[VARIABLE]"] != "" && Request.QueryString["[VARIABLE]"] != null)
    {
        query = "";
    }
    else
    {
        query = Request.QueryString["vslCat"];
    } 
    e.Result = (from b in context.tblVessels
                where b.vApproval == true
                where b.vCat == query
                select new
                {
                    b.vAdType,
                    b.vCat,
                    b.vID,
                    b.vAdTitle,
                    b.vAdDesc,
                    b.vBuilder,
                    b.vBuildYear,
                }).ToList();
}
protecte