a4j:repeat, ui:repeat or any other similar JSF components will not work in such role. See my answer at http://jboss.com/index.html?module=bb&op=viewtopic&t=106113
rich:columnGroup is useful when you want to apply some attributes (style* or on*) on the set of columns.
rich:columnGroup is very useful to build complex header or footer (as soon as facets do not accept several rich:column as children).
See the beginning of an incomplete article about rich:dataTable :
You can mix rich:column and rich:columnGroup, as well as h:column, t:column, t:columns
thanks for your reply.
1) I have read your post. you suggest use c:foreach to replace t:columns? i dont like c:foreach very much. and In the developper guide of facelets they suggest "The repeat tag should be used in almost all cases instead of the c:forEach to iterate over content with JSF".
2)I think your model columngroup is a little complex to use. for nested column , the ADFFaces has a better approach. I will be happy if i could have same thing in rich:datatable.
<af:column> <f:facet name="header"> </f:facet> <af:column> <f:facet name="header"> </f:facet> ....... </af:column> <af:column> <f:facet name="header"> </f:facet> ...... </af:column> </af:column>