title: Retrieving nested data from multiple records in a Firebase Database
body: <p>I'm trying to retrieve nested data from multiple records and display them in a ListView. My data is recorded like so: </p>
  
  <p><img src="https://i.stack.imgur.com/yQj2I.png" alt="The first ID is a groupID and the second is the groupVaccinationID"></p>
  
  <p>I want to display the GroupNumber and the GroupVaccinationDate of all GroupVaccinations recorded in a listView but at the moment the listView remains empty when I run the following code:</p>
  
  <pre><code>listView = (ListView)findViewById(R.id.listItemAllGroupVaccinations);
          databaseReference = FirebaseDatabase.getInstance().getReference("groupVaccinations");
          groupVaccinations = new ArrayList&lt;&gt;();
  
  protected void onStart(){
          super.onStart();
          databaseReference.addValueEventListener(new ValueEventListener() {
              @Override
              public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                  for(DataSnapshot groupVaccinationSnapshot : dataSnapshot.getChildren()){
                      GroupVaccination groupVaccination = groupVaccinationSnapshot.getValue(GroupVaccination.class);
                      groupVaccinations.add(groupVaccination);
                  }
                  AllGroupVaccinationList groupVaccinationInfoAdapter = new AllGroupVaccinationList(ActivityAllGroupVaccinations.this, groupVaccinations);
                  listView.setAdapter(groupVaccinationInfoAdapter);
  
              }
  
              @Override
              public void onCancelled(@NonNull DatabaseError databaseError) {
  
              }
          });
      }
  </code></pre>
  
  <p>Any help or suggestions would be greatly appreciated!</p>