This is now supported in the Application Builder using the 'Custom Single and Multiple Answer Questions' add on. For more information about how to turn on this feature please see Feature Previews.
|The instructions below are for advanced users only; Dimagi may not be able to help if you attempt to make changes to xml by hand and make a mistake.|
|Full access to this feature is only available for projects on a Standard software plan or higher. For more information, see https://www.commcarehq.org/pricing/|
Inside your form, you want to display existing cases in a checklist or single select question. To do this, you need to turn enable an Add On called "Custom Single and Multiple Answer Questions". This allows you to display custom choice lists in forms (i.e. a list of case sharing groups) instead of just items from a Lookup Table.
instance('casedb')/casedb/case[@case_type='your_type'](Replacing your_type with the case type you want to display)
[index/parent = instance('commcaresession')/session/data/case_id]
See also: Updating case properties based on the outcome of a multiple choice question