Selecting Items with Linq

Imar · April 7th, 2009, 01:23 PM

Can't you do both? That is, bind the Picttures collection to the Repeater and then execute another query against the same result to get the first picture? E.g. after the call to databind add another query that gets the first image as a string?

Imar

areed24 · April 8th, 2009, 12:03 PM

I'm sorry, but this just does not seem to be working. If I take the url out of the repeater, it won't be customizable with the rest of the information. Everything that I have tried results in the following error messages:

Quote:

An invalid data source is being used for Repeater1. A valid data source must implement either IListSource or IEnumerable.

or

Quote:

Sequence operators not supported for type 'System.String'

I really want to figure this out, but feel as though I am going in circles. All I want is a repeater with the Album Name and the First Picture in the Album beneath it. Is Linq the way to go or should I be looking elsewhere. I have lost a lot of valuable time working with this and can't find the right direction. Please help

Imar · April 8th, 2009, 01:00 PM

IMO, LINQ is the way to do it, but you need to know how to do it. You need to understand the data bound and you need to understand some LINQ and how it works. Also, clearly stating your requirements, and thinking a bit about your design up front really helps. I, for one, am a bit lost about what it is you want exactly. You say you want a single item, yet you query a collection and use a repeater.

The erorr message says you can't use a singular object for a repeating control. So, you either need to feed a collection to the Repeater, or drop the repeater in facor of some other control that can handle a single value like an Image, a HyperLink or something similar.

Which one is it? Whhat exactly are you trying to accomplish?

Imar

areed24 · April 8th, 2009, 01:56 PM

Instead of continuing in circles, I went back to the basics and wrote exaclty what I wanted to happen and tried to accomplish it step by step.

I created a page with a repeater that contains:
First Image in the Photo Album
Photo Album Name
Photo Album Id
Photo Album Owner

Code:

<div class="maintext">
       <asp:Repeater ID="Repeater1" runat="server">
        <ItemTemplate>
        <br/><asp:Image ID="Image1" ImageUrl="" runat="server" /><br />
        <br/><%#Eval("Name")%>
        <br/><%#Eval("Id")%>
        <br/><%#Eval("UserName")%> <br />
        </ItemTemplate></asp:Repeater>
        <p>
      <asp:Label ID="Label1" runat="server"></asp:Label> </p>
</div>

In the CB Page, I created the data source to get the Photo Album Name, ID, and Owner

Code:

Using myDatabaseContext As MyDataContext = New MyDataContext()
            Dim allAlbums = From albums In myDatabaseContext.PhotoAlbums _
                            Select albums.Name, albums.Id, albums.UserName
           
            Repeater1.DataSource = allAlbums
            Repeater1.DataBind()

This provided me with everything but the first picture in the photo album. So I went back and added a for each loop to see if I could correctly generate the first picture in the albums correctly:

Code:

 For Each album In allAlbums
                Dim albumId = album.Id
                Dim firstPic As String = (From pics In myDatabaseContext.Pictures _
                                          Where albumId = pics.PhotoAlbumId _
                                Select pics.ImageUrl).FirstOrDefault()
                Label1.Text += firstPic + "<br/>"

            Next

This produced a label with the url for the first picture in each album, exactly what I wanted.

What I can't do and haven't been able to do is find a way to bind the url's produced in the for each loop to the images in the repeater. Every time that I try to access the control using Repeater.FindControl("Image1") I an error. I apologize for the confusion. I am new to this and too stubborn to give up.

Imar · April 9th, 2009, 02:47 AM

Right, I think I finally understand your requirements. My initial example gave you the*first* albym, while you're after the first *picture* for each album. Something like this should work:

Code:

 
var albumWithFirstPic = from a in myDataContext.PhotoAlbums
     orderby a.Name
     select new { a.Name, FirstPicture = a.Pictures.FirstOrDefault() };

This selects the Album name and its first picture. You then get an anonymous type with a Name proeprty as a string and a FirstPicture property as a Picture which you can address in the Repeater like this:

Code:

 
<asp:Repeater ID="Repeater1" runat="server">
  <ItemTemplate>
    <h3><asp:Literal ID="Literal1" runat="server" Text='<%# Eval("Name") %>'></asp:Literal></h3>
    First Image: 
    <asp:Image ID="Image1" runat="server" ImageUrl='<%# Eval("FirstPicture.ImageUrl") %>' ToolTip='<%# Eval("FirstPicture.ToolTip") %>' />
  </ItemTemplate>
</asp:Repeater>

Notice statements like FirstPicture.ImageUrl to address the complex property type on the data item.

Hope this helps,

Imar

areed24 · April 9th, 2009, 07:26 AM

Thank you so much. I finally got the desired results. I used the first or default, but didn't assign a name to it. Thanks again!!!

Imar · April 9th, 2009, 12:30 PM

You're welcome...

Rather than (or in addition to) posting a Thank You message, you can also click the Thank You button at the bottom of the relevant posts.... ;-)

Cheers,

Imar