To display entity , use list view . Inside list view use group box to display values of an entity. Inside the group box widget, use one more list view to show cases associated with entity.
In this case I would place two datagrids on the page next to each other.
The first one being the datagrid with entities you already have.
The other one you set to show cases, but as a datasource you set listen to widget. This datagrid will now show the cases associated with the selected entity in the first datagrid. Alternatively you can use a listview instead of the second datagrid, depending on what you want to achieve.
Hope this helps!