title: firebase, how to update data at a key
body: <p>I have some difficulties in updating an object at a bucket (key). 
  At the time of persistence, I <code>push()</code> a list of objects (in this case, Trip) to a node. 
  Later, I retrieved it, and make an update (in this case, updating the bid info) when a button is clicked. I can't seem to find an easy way to do that, unless when I had pushed the trip before, I had to manually call <code>getkey()</code> and then update the auto-generated uid to the object Trip itself. Any idea to get it done easily? thanks</p>
  
  <pre><code>mFirebaseAdapter = new FirebaseRecyclerAdapter&lt;Trip,
              TripViewHolder&gt;(
              Trip.class,
              R.layout.item_message,
              TripViewHolder.class,
              mFirebaseDatabaseReference.child(CHILD_TRIPS)) {
  
          @Override
          protected void populateViewHolder(TripViewHolder viewHolder, final Trip model, int position) {
  
              viewHolder.btnTakeNow.setOnClickListener(new View.OnClickListener() {
                   @Override
                   public void onClick(View v) {
  
                       Bid bidAtReserved = new Bid(mDriverCarInfo, model, MY_PRICE);
  
                       mFirebaseDatabaseReference.child(CHILD_TRIPS)
                               //here, I want to update the bidding to this trip, but 
                               //I can't get the uid of the trip, unless I had 
                               //manually recorded at the time of pushing the trip
                               .child(model.getUid()) 
                                .child("bids").push().setValue(bidAtReserved);
  
  
                   }
              });
          }
      };
  </code></pre>