how to customize plone 4 collection to sort by multiple fields

I'm building a Plone 4.1 based site and am trying to find the best way to either sort a collection by multiple sort criteria, or at least customize a collection portlet to do so for the font page of the site. I believe the portlet uses the collection sort settings unless you choose random. Here is the section of code from the standard results in the portlet:

def _standard_results(self):
    results = []
    collection = self.collection()
    if collection is not None:
        limit = self.data.limit
        if limit and limit > 0:
            # pass on batching hints to the catalog
            results = collection.queryCatalog(batch=True, b_size=limit)
            results = results._sequence
        else:
            results = collection.queryCatalog()
        if limit and limit > 0:
            results = results[:limit]
    return results

For example, I would like to be able to sort by Expiration Date if present, if not then use the Creation Date for example. Or sort by tags and Creation Date. Any feedback on the best approach to this would be appreci开发者_如何学Cated.

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as ross said you'll need AdvancedQuery to sort on multiple criteria. if you just need this for the frontpage i'd suggest do create a custom portelt based on the collectionportlet.

where the collectionportlet calls collection.queryCatalog() you'll want to add some additional logic for your sorting:

>>> uids = [brain.UID for brain in collection.queryCatalog()]
>>> query = AdvancedQuery.In('UID', uids)
>>> results = catalog.evalAdvancedQuery(query, (('sortable_title', 'asc'), ('date', 'desc')

then you can use results instead of the results in your code sample above

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As in this answer, multiple sort is only available through AdvancedQuery an there's no integration of AdvancedQuery into collections that I'm aware of. So basically this isn't possible unless you integrate AdvancedQuery into collections yourself, which would be a non-trivial task.

A hackish workaround might be to use plone.indexer to write an indexer that returns the right sort value according to your logic, create a new FieldIndex in the catalog (profiles/default/catalog.xml), register that new index as valid for sort criterion in profiles/default/portal_atct.xml, then use that as your sort index.