Question

我在使用rawQuery获取游标以在ExpandableListView中使用时遇到了一些麻烦。我有一个名为ExpandableDataAdapter的适配器类，它扩展了SimpleCursorTreeAdapter。以下是我必须创建ExpandableDataAdapter实例的行：

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 }
      );

在ExpandableDataAdapter类定义中，我有以下方法来获取组游标的子游标：

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;
}

以上查询有效，并显示ExpandableListView。但是，当然，上面是我想要执行的实际查询的更简单版本。当我用实际（并且稍微复杂一点）的查询替换它时，我得到一个例外。首先，查询：

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;
}

我得到的例外是：列'房间'不存在。这个最新的查询在数据库提示符下运行正常，所以我猜测在android引擎执行时会发生一些事情。此外，异常声明也让我感到难过。我用了太多桌子吗？ group_concat函数是否会造成麻烦？有什么指针吗？

更多注意事项：从适配器的构造函数抛出异常，其定义如下。我正在调用构造函数，如本文的第一个片段所示。

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

这是你的SQL的一个问题。您只能选择Group By子句中的字段。 SELECT子句中的所有其他字段必须是聚合。因此，如果您的数据集可以实现，则可能必须将t2.TrackName和t1.Room添加到Group By子句中。

Answer 2

想出来 - 看起来我必须在第二个查询中显式声明列名。坦率地说，我不确定这是否确实是问题，或者这是否是正确的解决方案，但在列表中，ExpandableListView正在显示。工作片段是：

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")) });

SimpleCursorTreeAdapter中来自rawQuery的Cursor问题：表太多了？

2 个答案: