Class v.c.a.i.Placeholder(object):

Wrap an existing Item type to provide a different name for it.

This can be used to join a table against itself which is useful for flattening normalized data. For example, given a schema defined like this:

   class Tag(Item):
       taggedObject = reference()
       tagName = text()


   class SomethingElse(Item):
       ...

It might be useful to construct a query for instances of SomethingElse which have been tagged both with "foo" and "bar":

   t1 = Placeholder(Tag)
   t2 = Placeholder(Tag)
   store.query(SomethingElse, AND(t1.taggedObject == SomethingElse.storeID,
                                  t1.tagName == u"foo",
                                  t2.taggedObject == SomethingElse.storeID,
                                  t2.tagName == u"bar"))

Method	__init__	Undocumented
Method	__cmp__	Provide a deterministic sort order between Placeholder instances.
Method	__getattr__	Undocumented
Method	getSchema	Undocumented
Method	getTableName	Undocumented
Method	getTableAlias	Undocumented