LINQ TO SQL 中多表查询问题（急求）
class表：
CREATE TABLE CLASS(
classID INT IDENTITY(1,1) NOT NULL,
adress varchar(50) not null,
subject varchar(20) not null
primary key(classID)
)

students表：
CREATE TABLE student(
ID INT IDENTITY(1,1) NOT NULL,
sno int not null,
[sname] varchar(20) not null,
classID INT NOT NULL,
invID INT NOT NULL
PRIMARY KEY(ID),
foreign key(classID) REFERENCES CLASS(classID),
foreign key(invID) references teacher(invID)
)

teacher表：
create table teacher
(
invID INT IDENTITY(1,1) NOT NULL,
[name] varchar(20) not null,
primary key(invID),
)

要查询关键字 sno 显示为：
sno sname adress subject sname的形式。高手帮忙看下我哪里错了？？？

<asp:GridView ID="GridView2" runat="server" AutoGenerateColumns="False" 
  DataKeyNames="ID" onrowcommand="GridView2_RowCommand">
  <Columns>
  <asp:TemplateField HeaderText="学号" SortExpression="sno">
  <ItemTemplate>
  <asp:Label ID="Label_ID" runat="server" Text='<%#Eval("sno") %>'></asp:Label>
  </ItemTemplate>
  </asp:TemplateField>
  <asp:TemplateField HeaderText="考生名" SortExpression="sname">
  <ItemTemplate>
  <asp:Label ID="Label_load" runat="server" Text='<%#Eval("sname") %>'></asp:Label>
  </ItemTemplate>
  </asp:TemplateField>
  <asp:TemplateField HeaderText="教室" SortExpression="class">
  <ItemTemplate>
  <asp:Label ID="Label_price" runat="server" Text='<%#Eval("adress") %>'></asp:Label>
  </ItemTemplate>
  </asp:TemplateField>
  <asp:TemplateField HeaderText="科目" SortExpression="subject">
  <ItemTemplate>
  <asp:Label ID="Label_stay" runat="server" Text='<%#Eval("subject") %>'></asp:Label>
  </ItemTemplate>
  </asp:TemplateField>
  <asp:TemplateField HeaderText="监考" SortExpression="name">
  <ItemTemplate>
  <asp:Label ID="Label_traffic" runat="server" Text='<%#Eval("name") %>'></asp:Label>
  </ItemTemplate>
  </asp:TemplateField>
  </Columns>
  </asp:GridView>

cs内：

protected void GridView2_RowCommand(object sender, GridViewCommandEventArgs e)
  {
  var tr = from a in db.students
  join b in db.CLASS on a.classID equals b.classID
  join c in db.teacher on a.invID equals c.invID
  where a.sno == Session["sno"]
  select new
  {
  a.sno,
  a.sname,
  b.adress,
  b.subject,
  c.name,
  };
  GridView2.DataSource = tr;
  GridView2.DataBind();
  }
急求！！！！！！！！！！！！！！！

------解决方案--------------------
建议开启调试，查看TR中是否成功查询，以及SESSION中是否有对应的值。