How to bind a column to a child data object that is a list?

[Jonathan]

I have a grid that binds a number of child data objects to columns with no issue, using the syntax defined at http://www.telerik.com/help/aspnet-ajax/grdbindingtosubobjects.html.

What I cannot figure out, however, is how to aggregate a child object that is a list or collection. For example, if I have a Customer object and I want to get the customer's first street address, I would use DataField="Customer.Addresses[0].Street" on a standard GridBoundColumn.

How can I get the count of the addresses? I have tried all sorts of GridCalculatedColumn DataFields and Expressions, to no avail. I am looking for something along the lines of this:

<telerik:GridCalculatedColumn DataFields="Customer.Addresses"
Expression="Count( Child )" >

That doesn't work, of course. In fact, if I try to do a Count on any dotted data field, I get an exception of "System.Data.SyntaxErrorException: Syntax error in aggregate argument: Expecting a single column argument with possible 'Child' qualifier." For example, just trying to use an expression of "Count({0})" with DataFields set to "Customer.FirstName" (of which there is only one), causes that exception to be thrown at runtime. Doing the same thing with a non-dotted data field, such as SendDate, does not cause the same exception.

[Nikolay Rusev]

Hello Jonathan,

I am afraid that RadGrid does not support collections as DataFiled. The type that RadGrid binds must be  one of the following:
http://www.telerik.com/help/aspnet-ajax/grdbindablepropertytypes.html

Regards,
Nikolay
the Telerik team

[Jonathan]

Thanks for your reply. Does that mean it's not possible to do a Count off a child collection, as technically that data type would be an int?

[Nikolay Rusev]

Hello Jonathan,

The result of Count will be int. However DataField is not one of the bindable types, it is collection which is not supported.

Regards,
Nikolay
the Telerik team

[Jonathan]

Any thoughts on what alternative method I might employ to get that information? Can I create a column that's not actually databound and manually set it's value in something like the Page_Load? If so, how?

[Rosen]

Hi Jonathan,

You may consider using a TemplateColumn and call a custom function to retrieve and visualize the needed information from the current DataItem. Similar to the following:

 <telerik:GridTemplateColumn>
     <ItemTemplate>
         <%#CalculateAddressesCount((Customer)Container.DataItem)%>
     </ItemTemplate>
 </telerik:GridTemplateColumn>

code-behind:

protected string CalculateAddressesCount(Customer cust)
{
    return cust.Addresses.Count();
}

All the best,
Rosen
the Telerik team

[Daniel]

Hi,


And if I want to sort by that column, how can I do? I was thinking in something like:

SortExpression="<%#CalculateAddressesCount((Customer)Container.DataItem)%>"

but it doesn't work.

[Mark]

I am in the same situation.
Using Model Binding i am trying to count one of the relationships.
This works fine in a template field to get the value like so.
                <telerik:GridTemplateColumn HeaderText="Total Members" >
                    <ItemTemplate>
                        <%# Item.Member.Count() %>
                    </ItemTemplate>
                </telerik:GridTemplateColumn>

But i cant figure out how to get the sorting to work on this column.

[Radoslav]

Hello,

To achieve the desired functionality you need to add additional property into the datasource which returns the inner collection count. For example:

public class Helper
{
    public int ID { get; set; }
    public string Item { get; set; }
    public List<Helper1> Member { get; set; }
    public int MembersCount
    {
        get
        {
            return Member.Count;
        }
    }
}

public class Helper1
{
    public int ID1 { get; set; }
}

Then you can use this field as a sort expression:

<telerik:GridTemplateColumn HeaderText="Total Members" SortExpression="MembersCount">
                    <ItemTemplate>
                        <%# Item.Member.Count() %>
                    </ItemTemplate>
                </telerik:GridTemplateColumn>

Additionally I am sending you a simple example which demonstrates this approach.

I hope this helps.

Regards,
Radoslav
Telerik

 

 

[Mark]

The issue is I am using entity framework.
So using the above method gives me the following error:
The specified type member "MembersCount" is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.

any ideas?

Thanks

[Radoslav]

Hi Matt,

In this case you need to add additional column into the database and re-generate the Entity Framework model. This column can be populated with a TRIGGER where when a row is added it can update the values. More information about triggers you can find here:
http://msdn.microsoft.com/en-us/library/ms189799.aspx

I hope this helps.

Regards,
Radoslav
Telerik

 

 

[Raph]

I want to add a custom property in radgrid SP webpart that lets me choose  the data source as another SP list. Is that customization possible?

[Radoslav]

Hello Raph,

Please check the following forum thread which elaborate on the same matter:
http://www.telerik.com/forums/radgrid-from-sp2010-webpart-column-aggregates

I hope this helps.

Regards,
Radoslav
Telerik