I am looking for a way to get the entire object graph back from one of my nhibernate persisted entities. Is there a way to turn off lazy loading in a sessionfactory,session or query?
I have tried setting the FetchMode but it does not eagerly load the entity and child collections.
I just need this for one object to export it out of the database.
You can use CreateMultiQuery or CreateMultiCriteria and keep the default behavior to lazy loading in your mapping.
Take a look at this article for details.
Related
I am not understanding the following scenario. I have a situation where I need to load children and grandchildren along with an entity. I have specified that collections are lazyloaded, but eagerly fetch all rows using detached criteria and setfetchmode to eager. I have the following problem:
NHibernate is taking very long to hydrate the objects - the actual queries run quickly though.
I place the list of results into .net MemoryCacheManager object and seems that after a while the grandchildren seem to drop out the object and I get a lazyload exception.
How to I ensure that the entire graph returned by the results remains in tact in the MemoryCacheManager object? Does session.Evict help me?
Ended up using QueryOver future queries and flattened the results into a DTO and ended up caching the DTO.
I have set NHibernate to not lazy load for my entities. But sometimes when I do queries I don't want all the children of the children to be loaded. The mapping is set up by Fluent NHibernate.
Is there any way when writing the sql for the query to specify which columns to lazy load?
I believe, you're using the wrong approach. Set all mappings to lazy load, and then in the queries eager load only what you really need. This way you won't kill the app.
You can override all the mappings defined in Fluent Mappings in conventions either in class mappings.
There also are different scenarios where NHibernate does the trick (for instance if you load / get one instance all the properties will be fetched as defined in mapping. If you get a list of items it will not happen unless you use Fetch method explicitly).
So could you provide some more details on your question to give an answer that is more precise?
I have entities which I would like to eagerly load , and on other ocassions lazy (or even extra lazy) load.
My mappings have no fetch mode declared in my YAML- so they use the default (lazy loading).
Currently the only way to eagerly load is to by constructing the DQL manually - and I need to update this every time I add a new entity.
Ideally I would just load the root entity and the force eager loading all the associated objects. Is there any way I can do this?
If not why (is there a reason beyond it being an unimplemented feature)?
If you want to use built-in repository methods (find(), findAll()), you're probably out of luck unless you set things to eagerly load in your annotations.
You'll probably want to use the query builder (or raw DQL) in some custom repository's method to force eager loading where you want it. Yes, you'll have to update that method as you add entities, but at least you'll always know what's going on in regards to lazy/eager loading, and you'll only need to maintain it all in one place.
I suppose the reason there's not some $eagerLoad flag to find(), etc, is because those are convenience methods for simple tasks. If you wanted to add such a flag, you'd have quickly get into situations where you'd want to limit recursive eager loading by depth. You'd also probably have to start worrying about cyclical references (any bidirectional association, for instance).
You can use setFetchMode() method of DQL to set mode.
See the documentation:
https://web.archive.org/web/20120601032806/http://readthedocs.org/docs/doctrine-orm/en/latest/reference/dql-doctrine-query-language.html
How can I get NHibernate to hook up child objects automatically or bulk load children rather than lazy loading for each parent?
I have a large number of parent objects all of the same type. Each of them has two bags of child objects. As I need to load all the parents and children objects as quickly as possible, I use NHibernate to load all the objects and then loop all child objects and add them to relevant parent in code. I'm sure NHibernate has a much better way of doing this - but what is it?
You can always use eager loading behavior of NHibernate to override its default behavior (Lazy Loading).
Here is an article that discuss lazy loading and eagerly loading
Take a look at the "Eagerly loading with HQL" part that shows how you can use HQL to eagerly load an object graph.
However using eager loading can have a negative impact on performance specially if you are working with a lot of objects.
I'm using nhibernate to load parent class in a not lazy way
and I have many-to-many set of child class that I want to determine in run time rather to load it lazy or not.
I'm using .hbm.xml mapping and I tried to change the set "lazy" property after loading the assemblies, is it possible?
I think the best (only) way is to set lazy=false and then in your HQL use "join fetch" or in criterias use SetFetchMode on a collection that needs to be eagerly retrieved.
Read more here: http://ayende.com/Blog/archive/2006/05/02/CombatingTheSelectN1ProblemInNHibernate.aspx
/Asger