❔ How to join 3 collections?

var territoriesIDs = _parameters.TerritoriesIDs;

var accessGroups = await _accessGroupClient.GetByTerritoriesIds( territoriesIDs );
var accessGroupsIds = accessGroups.Select( accessGroup => accessGroup.Id );

var departments = await _departmentClient.GetByAccessGroupsIds( accessGroupsIds );
var departmentsIds = departments.Select( department => department.Id );

var subjects = await _subjectClient.GetByDepartmentsIds( departmentsIds );