is it possible in Fluent NHibernate to enable or disable Lazy loading in execution time?
In some cases when I retrieve an object I need the Many relation to be lazy loaded and in other cases I don't want.
Thanks in advance
Short answer: no.
You should map the association as lazy (this is the default), and when required, use a fetch load query.
Related
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
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.
When must we use eager loading in NHibernate? What is it's usage?
One usage is when you will cache or store an object graph (in ASP.NET Cache for instance). If you don't store the whole graph, you would be missing information on a detached object. You can reattach objects of course, but that would probably be a new roundtrip to the database anyway.
If you don't eager load your collections, you would need to touch every one of the to invoke the lazy fetch. In those cases, an eager fetch is much more useful.
Maybe this presentation by Udi can help you decide.
http://www.infoq.com/presentations/Making-Roles-Explicit-Udi-Dahan
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