[Hibernate] New laziness rules

[Gavin King]

As you guys probably know, I have been doing a lot of thinking about how to orthogonalize the notion of eager/lazy from the notion of fetch strategy (the actual SQL). And I want to do this in a way which allows a good implementation of EJB3 fetching contract, and remains reasonably compatible with what we have today. Oh, and I want to also try and reduce the number of newbie forum posts.   The basic concept is that association mappings have both:   fetch attribute lazy attribute   For single-valued associations:   fetch = “select|join” lazy = “true|false|proxy”   where lazy = “true” means use instvar interception, and lazy = “proxy” means use the proxy of the associated class (if it has one).   For collection-valued associations:   fetch = “select|join|subselect” lazy = “true|false”   where lazy = “true” is the usual lazy collection fetching we know and love (or hate).   For the second join of a many-to-many   fetch = “select|join” lazy = “false|proxy”   Note that this is a special case, since fetch = “join” is the default!   So, here are the new rules:   (1)   if lazy is specified, use the specified laziness semantics (2)   if lazy is not specified and fetch = “join”, assume lazy = “false” (3)   if lazy is not specified and not fetch = “join” a.      for collections, assume the default-lazy (almost always “true”) b.      for single-valued associations, assume “proxy”   Only rule (2) is suspect. We don’t need it, and I can get rid of it if you guys like. I’ve added it because I think it might help reduce the number of forum questions from people who wonder “why do I get lazy fetching when fetch=join?”.   Note that the association-level lazy setting is now *completely respected*. if I run a HQL query and some of the objects in the result set have non-lazy associations, those associations will be *immediately fetched*.