Question

I am having some trouble in using a rawQuery to get a cursor for use in an ExpandableListView. I have an adapter class called ExpandableDataAdapter which extends SimpleCursorTreeAdapter. Here is the line I have to create an instance of the ExpandableDataAdapter:

ExpandableDataAdapter confDataAdapter = new ExpandableDataAdapter(
       this,
       groupCursor,
       R.layout.detaillist_group,
       new String[]{ "TrackName" },
       new int[]{ R.id.rowText },
       R.layout.detaillist_child,
       new String[]{ "Title", "Speakers", "TrackName", "Room" },
       new int[]{ R.id.sessionTitle, R.id.sessionSpeakers, R.id.sessionTrack, R.id.sessionRoom }
      );

Inside the ExpandableDataAdapter class definition, I have the following method to get the children cursor for a group cursor:

protected Cursor getChildrenCursor(Cursor groupCursor) 
{
     // Given a group, return a cursor for all the children in that group.
     Cursor talksCursor = _db.rawQuery("SELECT t1.TalkID as _id, t1.Title," +
     " 'None' as Speakers, t2.TrackName, t1.Room" +
     " from talks t1, tracks t2" +
     " where t1.TrackID = t2.TrackID" +
     " and t2.TrackID=?", new String[]{ groupCursor.getString(groupCursor.getColumnIndex("_id")) });   
   startManagingCursor(talksCursor);
   return talksCursor;
}

The above query works, and the ExpandableListView shows up. But, of course, the above is a simpler version of the actual query which I want to execute. When I replace it with the actual (and somewhat more complicated) query, I get an exception. First, the query:

protected Cursor getChildrenCursor(Cursor groupCursor) 
{
   // Given a group, return a cursor for all the children in that group.
   Cursor talksCursor = _db.rawQuery("SELECT t1.TalkID as _id, t1.Title," +
     " group_concat(t3.Speaker, ', ') as Speakers, t2.TrackName, t1.Room" +
     " from talks t1, tracks t2, talkspeaker t3" +
     " where t1.TalkID = t3.TalkID" +
     " and t1.TrackID = t2.TrackID" +
     " and t2.TrackID=?" +
     " group by _id, t1.Title, t2.TrackName, t1.Room", 
      new String[]{ groupCursor.getString(groupCursor.getColumnIndex("_id")) });
   startManagingCursor(talksCursor);
   return talksCursor;
}

The exception I get is: column ‘Room’ does not exist. This latest query works fine from a database prompt, so I am guessing that something is happening when being executed by android engine. Also, the exception statement has me stumped as well. Am I using too many tables? Is the group_concat function creating trouble?
Any pointers?

More notes: the exception is thrown from the constructor of the adapter, which is defined as follows. I am calling the constructor as shown in the first snippet in this post.

public ExpandableDataAdapter(Context context, Cursor cursor,
      int groupLayout, String[] groupFrom, int[] groupTo,
      int childLayout, String[] childFrom, int[] childTo) 
 {
       super(context, cursor, groupLayout, groupFrom, groupTo, 
                             childLayout, childFrom, childTo);
 }

Answer 1

Figured it out – looks like I had to explicitly declare the column names in the second query. Frankly, I am not sure if this was indeed the problem or if this is the correct solution, but at list, the ExpandableListView is showing up. The working snippet is:

Cursor talksCursor = _db.rawQuery("SELECT t1.TalkID as _id, t1.Title as Title," +
        " group_concat(t3.Speaker, ', ') as Speakers, t2.TrackName as TrackName, t1.Room as Room" +
    " from talks t1, tracks t2, talkspeaker t3" +
    " where t1.TalkID = t3.TalkID" +
    " and t1.TrackID = t2.TrackID" +
    " and t2.TrackID=?" +
    " group by _id, t1.Title, t2.TrackName, t1.Room", 
        new String[]{ groupCursor.getString(groupCursor.getColumnIndex("_id")) });