PersistentQuery proxy for use in Collection or Sequence

QueryLinks are designed primarily for use with relational databases and other systems that implement one-to-many relationships via a pointer on the "one" side, and a query on the "many" side. The QueryLink is used on the "many" side, while the "one" side is implemented via a straightforward load/save on the "pointer" (foreign key).

A QueryLink is a proxy for use in an object's loaded state, to reference a persistent query whose contents represent the value of a collection or sequence property. Using a QueryLink keeps changes to the object from affecting the underlying query, and they also prevent execution of the query if the object is modified without actually looking at the results of the query.

In this way, if you have a collection with 10,000 things in it ("virtually"), it isn't necessary to load the list of 10,000 things to add an item to it. What happens is that if the query hasn't already executed, the QueryLink ignores the modification attempts (under the assumption that if you look at the collection later, the query will execute and be up-to-date). If the query has executed, the QueryLink makes a copy of the query results, and modifies the copy.

Last, but not least, whenever any operation (whether read or write) is performed on a QueryLink, it checks whether the data in the underlying query has been refreshed since the QueryLink made a copy of it, and if so, discards its local copy.

Normal usage looks like this (in a DM's _load() method):

        return {'someCollection': QueryLink(aQueryDM[foreignKey]), ...

__delitem__ ( self,  i )

__delslice__ (
        self,
        i,
        j,
        )

__iadd__ ( self,  other )

__init__ ( self,  query )

__isActive ( self )

__setitem__ (
        self,
        i,
        item,
        )

__setslice__ (
        self,
        i,
        j,
        other,
        )

append ( self,  item )

data ( self )

extend ( self,  other )

insert (
        self,
        i,
        item,
        )

remove ( self,  item )