Hi!
Some time ago we discussed whether we could add extra information on an
Association. At the time we concluded no, but I have had a discussion
about it again with a fellow Jaywayer. Here's an alternative syntax that
might work.
Instead of making specialized subtypes of ManyAssociation and
Association we could simply introduce something that can be referenced
and which includes both the associated object and the properties for the
association. Example:
interface Movie
{
ManyAssociation<AssociationRole<Actor,ActorRole>> actors();
}
interface ActorRole
{
Property<String> roleName();
}
with this one could do:
Actor superstar = ...;
ActorRole villain = ...;
movie.actors().add(new AssociationRole(superstar,villain));
where AssociationRole looks something like
public final class AssociationRole<A,R>
{
A association;
R role;
public AssociationRole(A a, R r)
{
association = a;
role = r;
}
public A association();
public R role();
}
Making it a class instead of an interface makes it easy for EntityStores
to detect it during storing and create new instances of it during
loading, and also makes it trivial to instantiate new roles in client
code as above. If the R side points to another Entity it is even
possible to update that without having to "re-set" the AssociationRole.
If it points to a value-object the owning association would have to be
set again whenever it is to be updated. Both have pros and cons.
What say ye? Emil, how would this map to Neo for example?
Also, what would this do to indexing/querying? How hard would it be to
make it work do you think?
/Rickard
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