I have a DataContext created with the designer, that has some one-to-many associations between tables. When I try to access those entities in an Repeater control that gets data from a LINQ Data Source, I get a NullReferenceException. Here is an example of code:

<asp:Repeater runat="server" DataSourceID="LatestArticlesDataSource">
  <ItemTemplate>
    <li>
      <!-- This shows the title of the article -->
      <h1><%# ((Article)Container.DataItem).Title %></h1>

      <!-- This throws NullReferenceException -->
      <h2><%# (((Article)Container.DataItem).Category.Title %></h2>
    </li>
  </ItemTemplate>
</asp:Repeater>

'Article' is a LINQ entity and it's of form:

public partial class Advice : INotifyPropertyChanging, INotifyPropertyChanged
{
  ...

  [Association(Name="Category_Article", Storage="_Category", ThisKey="CategoryID", IsForeignKey=true)]
  public Category Category { get { ... } set { ... } }
  
  ...
}

The DataContext and the entity-related classes are written corectly, as I've tested directly in C# and LINQ the column associations, and it worked perfectly.

So, how can I solve this problem?

Thanks!
 

Hi:

  It's a tricky problem since LinqDataSource is relevant new for users. Please try something like this. In my sample there're two tables, "Student" and "Class". Student table has a foreign key ClassID that is the pk of Class table.

        public string Func(object o)
        {
            string result = "";

          Class c=  DataBinder.Eval(o, "Class") as Class;
          result += c.ClassName + "<br/>";
          IEnumerable list = DataBinder.Eval(o, "Students") as IEnumerable;

          foreach (Student st in list)
          {
              result += st.StudentName + "&nbsp;";
          }
            return result;
        }

  <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false"
            DataSourceID="LinqDataSource1">
            <Columns>
            <asp:TemplateField>
            <ItemTemplate>
            <%#Func(Container.DataItem)%>

</ItemTemplate></asp:TemplateField></Columns>
        </asp:GridView>

        <asp:LinqDataSource ID="LinqDataSource1" runat="server"
            ContextTypeName="WebApplication5.DataClasses3DataContext" GroupBy="Class"
            Select="new (key as Class, it as Students)" TableName="Students">
        </asp:LinqDataSource>

Student table:

 [Table(Name="dbo.Student")]
 public partial class Student : INotifyPropertyChanging, INotifyPropertyChanged
 {
  

...

 [Association(Name="Class_Student", Storage="_Class", ThisKey="ClassID", IsForeignKey=true)]
  public Class Class
  {

...

  }

Class table:

 [Table(Name="dbo.Class")]
 public partial class Class : INotifyPropertyChanging, INotifyPropertyChanged
 {
  

...

 [Association(Name="Class_Student", Storage="_Students", OtherKey="ClassID")]
  public EntitySet<Student> Students
  {

...

}

Regards