How to use a LinkButton inside gridview to delete selected username?

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C#

ASP.NET

Gridview

I have a "UserDetail" table in my "JobPost.mdf".
I have a "Gridview1" showing the column from "UserDetail" table,which has a primary key "UserName".
This "UserName" is originally saved using Membership class function.
Now I add a "Delete" linkbutton to the GridView1. This "Delete" is not autogenerate button,I dragged inside the column itemtemplate from ToolBox.
The GridView1's columns now become "Delete_LinkButton"+"UserName"(within the UserDetail table)+"City"(within the UserDetail table)+"IsAdmin"(within the UserDetail table)

What I need is that by clicking this "delete_linkButton",it will ONLY delete the entire User Entity on the same row (link by the corresponding "UserName") from the "UserDetail" table,as well as delete all information from the AspNetDB.mdf (User,Membership,UserInRole,etc).

I would like to fireup a user confirm,but not mandatory. At least I am trying to make it functional in the correct way.

for example:

Command UserName    City           IsAdmin
delete  ken         Los Angles       TRUE
delete  jim         Toronto         FALSE

When I click "delete" on the first row, I need all the record about "ken" inside the "UserDetail" table to be removed. Meanwhile, all the record about "ken" in the AspNetDB.mdf will be gone, including UserinRole table.

I am new to asp.net, so I don't know how to pass the commandargument of the "Delete_LinkButton" to the code-behind file LinkButton1_Click(object sender, EventArgs e), because I need one extra parameter "UserName".

My partial code is listed below:

<asp:TemplateField>
                 <ItemTemplate>
                     <asp:LinkButton ID="Delete_LinkButton" runat="server" onclick="LinkButton1_Click1" CommandArgument='<%# Eval("UserName","{0}") %>'>LinkButton</asp:LinkButton>
                 </ItemTemplate>
             </asp:TemplateField>

protected void Delete_LinkButton_Click(object sender, EventArgs e)
     {
      ((LinkButton) GridView1.FindControl("Delete_LinkButton")).Attributes.Add("onclick", "'return confirm('Are you sure you want to delete {0} '" + UserName);
      Membership.DeleteUser(UserName);
      JobPostDataContext db = new JobPostDataContext();
      var query = from u in db.UserDetails
                   where u.UserName == UserName
                   select u;
         for (var Item in query)
         {
              db.UserDetails.DeleteOnSubmit(Item);
         }
      db.SubmitChanges();
     }

Please do help!
Thanks in advance.