This is not necessarily needed for 5.3.0, but I would like to get it into the 5.3 branch.
So far, there is one change to an SPI, Queryable#lazyGroupSelectFragment is added: public String lazyGroupSelectFragment( String tableAlias, String suffix, String fetchGroupName); The method gets implemented in AbstractEntityPersister. I don't think it's possible to create a default method in Queryable because the method needs access to private/protect methods in AbstractEntityPersister. If I don't get HHH-11223 in for 5.3.0, should I at least push the SPI change for 5.3.0? On Thu, Mar 1, 2018 at 9:55 PM, Gail Badner <gbad...@redhat.com> wrote: > Hi, > > Currently, when a lazy group is loaded that has associations, there are 2 > SQL statements executed. > > For example, suppose the DEFAULT lazy group contains the following: > > * Order#customer is a lazy many-to-one association; > > * Order#text is a lazy LOB. > > > When one of these properties is referenced, Hibernate loads both of them. > > > Currently, it takes 2 SQL statements to get the association loaded. > > > 1) Loads #text and the FK value for #customer (select o.text, > o.customer_id from orders o where o.id = ?) > > 2) Loads the state for #customer (select ... from customers c where c.id = > ?) > > > In other words, FetchMode.SELECT is used to load associations in a lazy > group. > > > HHH-11223 involves combining the 2 SQL statements into a single statement > using a join (i.e., using FetchMode.JOIN), but only when at least one of > the following is true: > > > * caching is disabled for the SessionFactory (e.g., > hibernate.cache.use_second_level_cache=false; > > * caching is not enabled for "get" operations (i.e., > session.getCacheMode().isGetEnabled() == false); > > * the associated entity type (and subclasses?) is not cached > > HHH-11223 only mentions to-one associations, but I think collections in a > lazy group could also be loaded using a join as well. > > I think I'm pretty close, but I need to do a lot more testing to ensure it > covers things like: > > * lazy association in composite ID > * lazy association in an embeddable > * lazy association in a secondary table > * lazy association in a subclass > * too many bags > > This is what I have implemented so far: https://github.com/ > hibernate/hibernate-orm/pull/2170 > > At the moment, I'm not looking for a comprehensive review. I'm just > looking for a review of the overall design. > > I don't want to get into the nitty-gritty here, but, basically, I've > created a new type of AbstractLoadPlanBasedEntityLoader, LazyGroupLoader, > which loads the lazy group properties into the existing entity. > > If caching is disabled for the SessionFactory, then one loader is > constructed per lazy group, and associations will be loaded using > FetchMode.JOIN. > > If caching is enabled for the SessionFactory, then 2 loaders are > constructed per lazy group. One loader is used when caching is enabled for > "get" operations (using Fetch.SELECT for cached associated > entities/collections; Fetch.JOIN for other associations). The other loader > is used when caching is disabled for "get" operations. > > Here are some of the changes to the default behavior (described above) > that could be useful: > > 1) Change all associations in lazy groups to be loaded using > FetchMode.SELECT (as is currently done without the fix), or using > FetchMode.JOIN (regardless of caching). A new configuration property could > be added: > > hibernate.bytecode.lazyGroup_association_fetchMode=(default | select | > join ) > > 2) Allow the FetchMode to be configured for a particular lazy association. > According to the documentation [1], @Fetch can't be used for this because, > "... FetchMode.JOIN acts as a FetchType.EAGER strategy. Even if we mark the > association as FetchType.LAZY, the FetchMode.JOIN will load the association > eagerly." > > A new annotation could be introduced: @LazyFetch. > > Comments or suggestions? > > Thanks, > Gail > > [1] http://docs.jboss.org/hibernate/orm/5.2/userguide/html_ > single/Hibernate_User_Guide.html#fetching-fetchmode-join > _______________________________________________ hibernate-dev mailing list hibernate-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev
