Dynamic动态数据类型（例如如何设置IQueryable的类型为函数返回的类型？？ ）

private IQueryable<Dynamic> GetArticleQueryByColumnID(long columnID)
{
string sqlStr = "";
if (columnID > 0)
{
sqlStr = string.Format(ExSql, string.Format(" and COLUMN_ID={0} ", columnID));
}
else
{
sqlStr = string.Format(ExSql, "");
}
switch (GetColumn(columnID).REFER_TYPE)
{
case 0:
return _db.ExecuteQuery<V_ARTICLE_SHOW_ALL>(sqlStr).AsQueryable();
case 1:
return _db.ExecuteQuery<V_ARTICLE_SHOW_REFER>(sqlStr).AsQueryable();
case 2:
return _db.ExecuteQuery<V_ARTICLE_SHOW_REFER>(sqlStr).AsQueryable();
case 3:
return _db.ExecuteQuery<V_ARTICLE_SHOW_DUTYTREE>(sqlStr).AsQueryable();
default:
return _db.ExecuteQuery<V_ARTICLE_SHOW_REFER_ALL>(sqlStr).AsQueryable();
}
}