If I understand correctly you have a hierarchical datasource and you have bound the Grid to the first level but when you are filtering you want to include the data from the inner level in the filtered data. Is that correct?
If this is the case I am afraid this is not available out of the box. The way to achieve your goal is to include both level into a single container. This could be done with Join if you are using SQL or Entity Framework or you could create a new array/list that will be filled with all the data.
Give these suggestions a try and you should succeed.
All the best,
the Telerik team
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