Replace default table sort with order by on the view object

Question

The Jdeveloper help for af:table says:
If the underlying model is not a CollectionModel , the Table automatically examines the actual data to determine which properties are sortable. Any column that has data that implements java.lang.Comparable is sortable. This automatic support cannot be nearly as efficient as coding sorting directly into a CollectionModel (for instance, by translating the sort into an "ORDER BY" SQL clause), but is sufficient for small data sets.
I have a database table with varchar2 columns that can contain string, date or number values. So in the af:table I want to sort the columns either in string, date or number order.
I tried creating a sort listener and in that listener set the view object order by clause and execute the query, but it does not affect the row order - it is always sorted as a string. I assume that the collection is doing its sort after I do the query, and overwriting the query order. I have tried disabling the sort in the listener by setting the sortcriteria to null but it has no effect.
Can anyone suggest how to stop the default sort re-ordering the rows, or else how to code sorting directly into the CollectionModel as suggested in the help.
Hugh Nelson

Answer 1

By running in debug I discovered that when you click on a column heading to sort by the column values it actually sets the order by clause on the view object and executes a query. The help says that the default sorting is not as efficient as setting the order by clause - perhaps the help is out of date because default sorting does set the order by clause.
This means that you cannot do a column sort on a transient attribute. The attribute being sorted on must exist in the table/query.
The easiest solution is to override the setOrderByClause method on the view object. The string parameter is the column to order by eg "COLUMNA". If this column holds date values I can change it to something like "TO_CHAR(TO_DATE(COLUMNA,'DD-MON-YYYY'),'YYYYMMDD')". For numbers I do "LPAD(COLUMNA,10,'0')".
This works OK.
Hugh Nelson