How to group a second datasource by the inventory dimensions set on the form

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I have a form with a grid and inventory dimensions button.
The form displays the ItemId, ItemName, UnitId and AvailPhysical, RelatedItemIds grouped by the active dimensions (for example Site and Location).

I’ve added an 2^nd grid that must show the additional data from the selected record (based on the values that are in the RelatedItems column) in the 1^st grid. This grid is bound to an temp table that is filled by a class when a record in the 1^st grid is selected (Active method on datasource 1^st grid).

The problem is that in the 1^st grid, there are dimensions set by the button (inventory dimensions) for example Site and Location. The result in the 2^nd grid isn’t grouped by the selected dimensions.

How can I achieve that?