I'm using Fluent NHibernate and try to do many updates. First came in mind is code like this:
using (ISession s = OpenSession())
using (s.BeginTransaction())
{
IList<SomeType> items s.QueryOver<SomeType>()
.Where(someCondition)
.List();
items.ForEach(i => {
i.Foo = "bar";
s.Update(i);
});
s.Transaction.Commit();
}
But problem is in that every updating item must be loaded before do update. So database queried twice. In SQL it can be done with one query and i believe exist some way to do this with one query in NHibernate. And found doc for Load method that not actually load item from db and only work with some proxy instead and hit database only when i do update/delete.
Exist some method in NHibernate that load not items itself but proxy like Load?
For now for update large data best way is use HQL or raw SQL how mentioned #DavidOsborne.
I unfortunately not found any other methods that works lazy as Load method.
I would like to override the default lazy loading behavior which is set in mappings as 'lazy=false'. Can't change it as many parts of existing application depend on this setting.
After spent some hours on it I didn't find a solution so I'm asking here.
How to do this?
What I want to achieve is to fine tune my query to load only what is needed.
This is what I've tried already:
Using QueryOver api:
var properties = session.QueryOver<Property>()
.Fetch(prop => prop.Transactions).Eager
.Fetch(prop => prop.Districts).Eager
//I dont want to load those entities below so I mark
//them as lazy - IT DOESN'T WORK
//I can see in SQL that they are getting loaded in separate queries
.Fetch(prop => prop.Districts.First().Aliases).Lazy
.Fetch(prop => prop.Districts.First().PolygonPoints).Lazy
.Skip(i * pageSize)
.Take(pageSize)
.List();
Using Criteria api:
var criteria = session.CreateCriteria<Property>();
criteria.SetFetchMode("Transactions", NHibernate.FetchMode.Join);
criteria.SetFetchMode("Districts", NHibernate.FetchMode.Join);
criteria.SetFetchMode("Districts.Aliases", NHibernate.FetchMode.Select); // tried Lazy too
criteria.SetFetchMode("Districts.PolygonPoints", NHibernate.FetchMode.Select); // tried Lazy too
criteria.AddOrder(NHibernate.Criterion.Order.Asc("Id"));
criteria.SetFirstResult(i * pageSize);
criteria.SetMaxResults(pageSize);
var properties = criteria.List<Property>();
Using any of the above methods 'Aliases' and 'PolygonPoints' are always being loaded when calling List<>(). I don't need them in my process.
I'm using Nhibernate 4.0.
Any ideas?
We cannot override mapping in this case. We can do it opposite way - have lazy in place - and use eager fetching for querying.
The decision process (of reference loading) is done outside of the query, ex post. So it could be pre-loaded, but cannot be avoided.
Solution here could be of two types.
The first is preferred (by me) - do your best and make laziness the default: Ayende -
NHibernate is lazy, just live with it
Use projections. Instruct NHibernate to create just one query, use transformer to get expected object graph - without any proxies in it
There is pretty clear example how to (properly) use projection list even for references:
Fluent NHibernate - ProjectionList - ICriteria is returning null values
And we would also need Custom result transformer, which will ex-post create all the references from the returned data:
Custom DeepResultTransfomer
I am trying get a record updated from database with QueryOver.
My code initially creates an entity and saves in database, then the same record is updated on database externally( from other program, manually or the same program running in other machine), and when I call queryOver filtering by the field changed, the query gets the record but without latest changes.
This is my code:
//create the entity and save in database
MyEntity myEntity = CreateDummyEntity();
myEntity.Name = "new_name";
MyService.SaveEntity(myEntity);
// now the entity is updated externally changing the name property with the
// "modified_name" value (for example manually in TOAD, SQL Server,etc..)
//get the entity with QueryOver
var result = NhibernateHelper.Session
.QueryOver<MyEntity>()
.Where(param => param.Name == "modified_name")
.List<T>();
The previous statement gets a collection with only one record(good), BUT with the name property established with the old value instead of "modified_name".
How I can fix this behaviour? First Level cache is disturbing me? The same problem occurs with
CreateCriteria<T>();
The session in my NhibernateHelper is not being closed in any moment due application framework requirements, only are created transactions for each commit associated to a session.Save().
If I open a new session to execute the query evidently I get the latest changes from database, but this approach is not allowed by design requirement.
Also I have checked in the NHibernate SQL output that a select with a WHERE clause is being executed (therefore Nhibernate hits the database) but don´t updates the returned object!!!!
UPDATE
Here's the code in SaveEntity after to call session.Save: A call to Commit method is done
public virtual void Commit()
{
try
{
this.session.Flush();
this.transaction.Commit();
}
catch
{
this.transaction.Rollback();
throw;
}
finally
{
this.transaction = this.session.BeginTransaction();
}
}
The SQL generated by NHibernate for SaveEntity:
NHibernate: INSERT INTO MYCOMPANY.MYENTITY (NAME) VALUES (:p0);:p0 = 'new_name'.
The SQL generated by NHibernate for QueryOver:
NHibernate: SELECT this_.NAME as NAME26_0_
FROM MYCOMPANY.MYENTITY this_
WHERE this_.NAME = :p0;:p0 = 'modified_name' [Type: String (0)].
Queries has been modified due to company confidential policies.
Help very appreciated.
As far as I know, you have several options :
have your Session as a IStatelessSession, by calling sessionFactory.OpenStatelesSession() instead of sessionFactory.OpenSession()
perform Session.Evict(myEntity) after persisting an entity in DB
perform Session.Clear() before your QueryOver
set the CacheMode of your Session to Ignore, Put or Refresh before your QueryOver (never tested that)
I guess the choice will depend on the usage you have of your long running sessions ( which, IMHO, seem to bring more problems than solutions )
Calling session.Save(myEntity) does not cause the changes to be persisted to the DB immediately*. These changes are persisted when session.Flush() is called either by the framework itself or by yourself. More information about flushing and when it is invoked can be found on this question and the nhibernate documentation about flushing.
Also performing a query will not cause the first level cache to be hit. This is because the first level cache only works with Get and Load, i.e. session.Get<MyEntity>(1) would hit the first level cache if MyEntity with an id of 1 had already been previously loaded, whereas session.QueryOver<MyEntity>().Where(x => x.id == 1) would not.
Further information about NHibernate's caching functionality can be found in this post by Ayende Rahien.
In summary you have two options:
Use a transaction within the SaveEntity method, i.e.
using (var transaction = Helper.Session.BeginTransaction())
{
Helper.Session.Save(myEntity);
transaction.Commit();
}
Call session.Flush() within the SaveEntity method, i.e.
Helper.Session.Save(myEntity);
Helper.Session.Flush();
The first option is the best in pretty much all scenarios.
*The only exception I know to this rule is when using Identity as the id generator type.
try changing your last query to:
var result = NhibernateHelper.Session
.QueryOver<MyEntity>()
.CacheMode(CacheMode.Refresh)
.Where(param => param.Name == "modified_name")
if that still doesn't work, try add this after the query:
NhibernateHelper.Session.Refresh(result);
After search and search and think and think.... I´ve found the solution.
The fix: It consist in open a new session, call QueryOver<T>() in this session and the data is succesfully refreshed. If you get child collections not initialized you can call HibernateUtil.Initialize(entity) or sets lazy="false" in your mappings. Take special care about lazy="false" in large collections, because you can get a poor performance. To fix this problem(performance problem loading large collections), set lazy="true" in your collection mappings and call the mentioned method HibernateUtil.Initialize(entity) of the affected collection to get child records from database; for example, you can get all records from a table, and if you need access to all child records of a specific entity, call HibernateUtil.Initialize(collection) only for the interested objects.
Note: as #martin ernst says, the update problem can be a bug in hibernate and my solution is only a temporal fix, and must be solved in hibernate.
People here do not want to call Session.Clear() since it is too strong.
On the other hand, Session.Evict() may seem un-applicable when the objects are not known beforehand.
Actually it is still usable.
You need to first retrieve the cached objects using the query, then call Evict() on them. And then again retrieve fresh objects calling the same query again.
This approach is slightly inefficient in case the object was not cached to begin with - since then there would be actually two "fresh" queries - but there seems to be not much to do about that shortcoming...
By the way, Evict() accepts null argument too without exceptions - this is useful in case the queried object is actually not present in the DB.
var cachedObjects = NhibernateHelper.Session
.QueryOver<MyEntity>()
.Where(param => param.Name == "modified_name")
.List<T>();
foreach (var obj in cachedObjects)
NhibernateHelper.Session.Evict(obj);
var freshObjects = NhibernateHelper.Session
.QueryOver<MyEntity>()
.Where(param => param.Name == "modified_name")
.List<T>()
I'm getting something very similar, and have tried debugging NHibernate.
In my scenario, the session creates an object with a couple children in a related collection (cascade:all), and then calls ISession.Flush().
The records are written into the DB, and the session needs to continue without closing. Meanwhile, another two child records are written into the DB and committed.
Once the original session then attempts to re-load the graph using QueryOver with JoinAlias, the SQL statement generated looks perfectly fine, and the rows are being returned correctly, however the collection that should receive these new children is found to have already been initialized within the session (as it should be), and based on that NH decides for some reason to completely ignore the respective rows.
I think NH makes an invalid assumption here that if the collection is already marked "Initialized" it does not need to be re-loaded from the query.
It would be great if someone more familiar with NHibernate internals could chime in on this.
I couldn't find an answer to this issue so I assume it is something I am doing wrong.
I have a PersistenceModel set up where I have set a convention as follows: -
persistenceModel.Conventions.Add(DefaultLazy.Always());
However, for one of the HasManyToMany relationships in one of my entities I want eager loading to take place which I am setting up as follows: -
HasManyToMany(x => x.Affiliates).Not.LazyLoad();
Intuitively, I expect eager loading to take place as I am overriding the lazy load default that I have specified as a convention but it still lazy loads. If I set the DefaultLazy convention to never and then set LazyLoad on an individual relationship it doesn't work either.
Any ideas?
When you set Not.LazyLoad(), you tell NHibernate to load Affiliates when the parent loads. NHibernate will do this by performing another select on the Affliates many-to-many table regardless of whether you access the Affiliates collection or not. NHibernate is using another select because that is the default fetching mode. You want to override fetching mode as well, either in the query or in the mapping. To do it in the mapping, add the following:
HasManyToMany(x => x.Affiliates)
.Not.LazyLoad()
.Fetch.Join();
You might also want to include a ".Cascade.AllDeleteOrphan()" if you want NHibernate to persist new Affiliaites added to the collection and delete orphaned ones. If you do not do this, you will have to explicitly call session.Save(newAffiliate). Otherwise you'll receive a TransientObjectException when your Affiliates collection contains a new Affiliate.
It may be one stupid thing to ask, but have you execute the query inside your session? Say,
Using(var session = OpenSession())
{
session.Query<Entity>().ToList();
}
I had this problem before, and finally realized the objects that I was accessing hadn't been queried before disposing the session.
I have a product table that has a many-to-many relation to itself (using a two-column many-to-many table) and I have set it up in Fluent NHibernate with the following code:
public class ProductConfiguration : ClassMap<Product>
{
public ProductConfiguration()
{
Table("Product");
Id(p => p.Id).GeneratedBy.Guid();
Map(p => p.Name).Not.Nullable().Length(254);
Map(p => p.Description).Not.Nullable().Length(1000);
Map(p => p.CreatedAt).Not.Nullable();
HasManyToMany(p => p.CrossSell)
.Table("ProductCrossSell")
.ParentKeyColumn("Id")
.ChildKeyColumn("ProductId");
}
}
My MVC application has two pages that uses this setup:
Index - Uses a generic repository GetAll method to display all products.
Detail - Uses a generic repository GetById method to display one product and any related cross sell products setup in the many-to-many realation.
It looks like NHibernate is set to LazyLoad the many-to-many by default so when I fire up the application and watch it in profiler I can see that it does LazyLoad the many-to-many with the following alert "Use of implicit transactions is discouraged".
How do I get rid of this alert? I couldn't find any information on how to wrap a LazyLoad inside a transaction to get rid the alert. Is it even possible?
Is there a way to not lazyload this by telling NHibernate that whenever I ask for GetById make sure to join the tables a get everything in one query? I tried using .Fetch.Join() in the many-to-many mapping but that also affected my GetAll query which now displays a joined result set as well which is incorrect.
What is the best apprach for this kind of simple scenario?
Thanks
The way to get rid of the warning is to access the object graph and fully populate the UI elements inside a single transaction.
Not by configuration. You can create an HQL query that eager fetches the association and use that query for a specific view. I would stick with lazy loading and not make that optimization unless needed. The HQL would be:
return session.CreateQuery("from ProductionConfiguration pc join fetch pc.CrossSell where pc.Id = ?")
.SetGuid(0, id)
.List<ProductConfiguration>();
All collections are lazily loaded in NHibernate by default.
You must be triggering loading with a call of some kind (maybe even with the debugger watches)