[SQLObject] related join design?

[Tracy S. R. <tr...@re...>]

This may be a broader question about relational information design, but 
I thought I'd put this out anyway.

I would like to build an object, say a 'node', that has a number of 
related 'items' based upon a particular 'context'.  In one context, for 
example, one particular node may 'contain' a certain of items, but 
contain other items in a different context.

Here's how I have it defined in SQLObject.  Does anyone see a better 
way to do this? Or, is there a better way to design associations 
between two sets of things that depends on the settings of a 3rd thing?

	class node(SQLObject):
		name = StringCol(length=32)
		itemAssociations = MultipleJoin('itemAssociation')
	
		def getItems(self, context):
			return [ia.item for ia in self.itemAssociations if ia.context == 
context]
		
		def getItems_ALT(self, context):
			# note: 'getItems' is 5-10% faster for small sets of items
			return [iaq.item for iaq in itemAssociation.select(AND(
					itemAssociation.q.nodeID==self.id,
					itemAssociation.q.contextID==context.id))]
	
		def associateItem(self, item, context):
			return itemAssociation.new(node=self, item=item, context=context)
	
	class itemAssociation(SQLObject):
		node = ForeignKey('node')
		item = ForeignKey('item')
		context = ForeignKey('context')
	
	class item(SQLObject):
		name = StringCol(length=32)
	
	class context(SQLObject):
		name = StringCol(length=32)

For now, I have a 'compile' method in 'node' that takes a context 
object as its first arg and returns a node and its information/items 
into a dictionary where its 'items' key is a list of item dictionaries, 
too.

Thanks,
--T