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Question

Answer 1

A:

Try binding the DropDownList DataSource to Pages property of your user object

<asp:GridView ID="GridView1" runat="server" DataSourceID="LinqDataSourceUsers" AutoGenerateColumns="false">
    <Columns>
        <asp:CommandField ShowSelectButton="True" />
        <asp:BoundField DataField="UserID" HeaderText="UserID" />
        <asp:BoundField DataField="Name" HeaderText="Name" />
        <asp:BoundField DataField="PageID" HeaderText="PageID" />
        <asp:TemplateField HeaderText="Pages">
        <ItemTemplate
            <asp:DropDownList ID="DropDownList1"
             DataSource='<%#Eval("Pages") %>'
             SelectedValue='<%#Bind("PageID") %>'
             DataTextField="Url"
             DataValueField="PageID"
             runat="server">
            </asp:DropDownList>
        </ItemTemplate>
        </asp:TemplateField>           
    </Columns>
</asp:GridView>

alejandrobog 2010-05-27 19:53:49

Thanks, but it didn't work. I got a message saying "Pages" doesn't exist. It came to me that I'm probably not setting up the relationship right. I think it has to be a many-to-many relationship. I'll edit the question...

Anders Svensson 2010-05-27 22:41:26

One to many works also, just verify the name of property in your linqToSql class and replace it in the DDL

alejandrobog 2010-05-27 22:45:33

Well, there was a "Page" property (since this was the "one" side of the relationship), but if I changed it to that I got the error message that the datasource has to be set to an IEnumerable, which makes sense I guess... I can't set the datasource to a property that returns a single Page object...

Anders Svensson 2010-05-27 22:56:52

Answer 2

A:

I've run into similar situations before with a ListView and LinqDataSources. The only solution i've found is to set the datasource for the DropDownlist in the OnRowCreated or OnRowDatabound events.

You can still use the LinqDataSource for your BoundFields but I suspect you might need to do the TemplateField in the code behind in this case.

Code:

<asp:GridView ID="GridView1" runat="server" OnRowCreated="GridView1_OnRowCreated" DataSourceID="LinqDataSource1" AutoGenerateColumns="false">
<Columns>
    <asp:CommandField ShowSelectButton="True" />
    <asp:BoundField DataField="UserID" HeaderText="UserID" />
    <asp:BoundField DataField="Name" HeaderText="Name" />
    <asp:BoundField DataField="PageID" HeaderText="PageID" />
    <asp:TemplateField HeaderText="Pages">
    <ItemTemplate>
        <asp:DropDownList ID="DropDownList1"
         DataSource='<%#Eval("Pages") %>'
         SelectedValue='<%#Bind("PageID") %>'
         DataTextField="Url"
         DataValueField="PageID"
         runat="server">
        </asp:DropDownList>
    </ItemTemplate>
    </asp:TemplateField>           
</Columns>

C#:

protected void GridView1_OnRowCreated(object sender, EventArgs e)
{
   //Create int variable with the UserId value
   //Create new Linq query to be used as datasource.  must get pages and filter by userid.
   //FindControl DropDownList1
   //use the linq query mentioned in the second comment  as the datasource for DropDownList1
   //DataBind DropDownList1

   //Example: 
int userId = /*get userid logic*/;
var userPages = from t in dc.Pages
                where t.UserId = userId
                select t;
((DropDownList)/*Find drop down list*/).DataSource = userPages;
((DropDownList)/*Find drop down list*/).DataBind()
}

Abe Miessler 2010-05-27 23:00:06

Right, I actually already got something working similar to this (but using only codebehind). I assume you mean using the one-to-many relationship here, though, right? Because otherwise I get the message I mentioned in my edit above, that the property Name doesn't exist on the junction object. I would really have wanted it to work with binding in the aspx page though, and I assume it should be done with many-to-many because that makes sense right? A user can hit many pages, and each page can have many users...

Anders Svensson 2010-05-27 23:28:06

I may not be understanding you correctly but take a look at the updated comments in my C# section and see if that resolves the problem. I'm suggesting that you create a new linq query for your dropdownlist on every RowCreated event. Does this make sense?

Abe Miessler 2010-05-28 00:01:14

Well, what I meant was that I had already accomplished this using codebehind, but what I wanted was to be able to do the binding directly in the control, and preferably using a many-to-many relationship, since I realized that is in fact the correct relationship. I was going to accept this and accept this as the answer even though it wasn't really what I was after, but I've seen a couple of web pages describing this problem, and I'm going to look into that first. Thanks anyway!

Anders Svensson 2010-05-28 13:48:35

Answer 3

+1 A:

Well, it seems I found the answer myself. This page explains the problems with many-to-many relationships and LINQ: http://blogs.msdn.com/b/mitsu/archive/2007/06/21/how-to-implement-a-many-to-many-relationship-using-linq-to-sql.aspx. Using that information I could modify the User class so that it has a property to return an IEnumerable collection. I added this to the class User (in the codebehind for the Linq context):`

    public IEnumerable<Page> Pages
    {
        get { return UserPages.Select(u => u.Page); }
    }

That way I could have the many-to-many relationship, and I could simply refer to the new Pages property in the aspx directly:

    <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="ManyToMany._Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt;
<html xmlns="http://www.w3.org/1999/xhtml"&gt;
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:GridView ID="GridView2" runat="server" DataSourceID="LinqDataSourceUsers" AutoGenerateColumns="false">
            <Columns>
                <asp:CommandField ShowSelectButton="True" />
                <asp:BoundField DataField="UserID" HeaderText="UserID" />
                <asp:BoundField DataField="Name" HeaderText="Name" />
                <asp:TemplateField HeaderText="Pages">
                    <ItemTemplate>
                        <asp:DropDownList ID="DropDownList1" DataSource='<%#Eval("Pages") %>' DataTextField="Url"
                            runat="server">
                        </asp:DropDownList>
                    </ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>
        <asp:LinqDataSource ID="LinqDataSourceUsers" runat="server" ContextTypeName="ManyToMany.UserPageDBDataContext"
            TableName="Users">
        </asp:LinqDataSource>
    </div>
    </form>
</body>
</html>

I hope this helps someone else who has been struggling with this like I did!

Anders Svensson 2010-05-28 13:58:10

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Databind gridview with LINQ

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