How to filter Grid on a column that is a list?

[Jason]

I populate the Grid with ~5000 results from a database. The Grid does the paging, sorting, and filtering in memory, except it won't filter for this one column that is a List<string> CustomerNamesList. I'm attempting to use the FilterMenuTemplate -- I just need a textbox and a dropdown like "Contains" and "Does Not Contain" but I can't figure out how to filter the Grid.

<GridColumn Field="@(nameof(CustomerNamesList))" Title="Customers" Sortable="false" Filterable="true">
    <FilterMenuTemplate>
        <label for="NameMenuFilter">Customer Name:</label>
        <TelerikTextBox Id="NameMenuFilter" ValueChanged="@((value) => UpdateCustomerNameFilter(value))"> 
        </TelerikTextBox>
    </FilterMenuTemplate>
    <Template>
        @* display - loop thru List of customer names *@ 
    </Template>
</GridColumn>

 

This code gets hit, but it's not doing anything...

public void UpdateCustomerNameFilter(string itemValue)
{
        var filter1 = partyNamesFilterContext.FilterDescriptor.FilterDescriptors[0] as FilterDescriptor;
        filter1.Value = itemValue;
        filter1.Operator = FilterOperator.Contains;
}

When I click Filter, it gives me a blazor.server.js error
Error: System.ArgumentException: Provided expression should have string type (Parameter 'stringExpression')

 

Update

Here's what I'm using as the datasource to make things clearer: IEnumerable<Companies>
So what it appears to me is that the Grid doesn't know how to filter on a List of objects like this List<string> 

public class Companies
{
  public int Id {get; set;}
  public List<string> CustomerNamesList {get; set;} = new List<string>();
  // Other fields
}
   

[Hristian Stefanov]

Hi Jason,

I tried to reproduce the described scenario on my end. It seems I cannot get the same result.

The problem might come from those little parts missing (like the Template content) from the provided example. I have also changed a little bit the Filed of the column from "@(nameof(CustomerNamesList))" -> "@(nameof(Sample.CustomerNamesList))", but this might be just a typo.

In order for me to be on the same page as you, could you please try to send me a little reproduction or a little more code snippets? This will be really helpful for us, and I will be able to investigate further.

By the way, you can see an example of an approach using FilterMenuTemplate in our demo here: https://demos.telerik.com/blazor-ui/grid/custom-filter-menu. You may find really useful additional information about your case.

Thank you.

Regards,
Hristian Stefanov
Progress Telerik

[Jason]

I've updated the question to make source clearer. I'm trying to filter on a list of strings, so I'm wondering if that is supported or not. The examples all use predefine types like String, Int, Date, and Bool.

[John]

I'd also like to know if there's a recommended way to filter a column with a list<string> in it.

[Hristian Stefanov]

Hello Jason,

I apologize for the misunderstanding. You are correct that in a Grid column field we support only the predefined types like the ones we use in our examples (string, int, date, bool..). This is the reason that causes a System.ArgumentException error.

The desired result can be achieved with the following approaches:

• Use the OnRead event to perform the filtering inside of it. This will let you customize your filter.

• Use the FilteMenuTemplate like in the demo from my previous answer.

I hope this helps. If you have any other questions, please let me know.

Regards,
Hristian Stefanov
Progress Telerik

[Jason]

Thanks for that confirmation. But you are saying it IS possible to have Telerik Grid filter a List<string> in either approach? I understand OnRead allows me to go retrieve a newly filtered result from the database or even in memory, but I was hoping we could get Telerik to do its own filtering.

I would be intrigued if I could do it using FilterMenuTemplate to filter the List<string>, but your demo only shows using string, int, date, bool. The example shows the use of FilterDescriptors and I'm wondering if I'm only a couple lines of code away from filtering on a List<string> ??

My only viable option right now is to get rid of the List<string> which reduces the usefulness of the Grid.

[David]

I have this exact same need and can't figure it out either.

[Marin Bratanov]

There isn't a built-in solution for this, as there isn't one in the framework. Comparison is not defined for collections and so we can't execute a filter or sort on anything but primitive (value) types. You can read more about this and a few other notes here: https://docs.telerik.com/blazor-ui/components/grid/columns/bound#notes

So, you will need to implement that specific filtering entirely in the business application code and I can't say what the best way to do that is, as it depends heavily on the situation.

What the grid gives you is:

• filter template so you can get the proper UI for collecting the info you need from the user
• the OnRead event that fires with filters you can create based on that information so you can implement the needed data source operations in your app/service/database (generally - code)

 

[Dimo]

Hi all,

For anyone who is interested in filtering a list property in the Grid, please refer to the linked knowledge base article.

Regards,
Dimo
Progress Telerik