I'm facing the same issue others already posted on SO: On reading objects from the database, NHibernate would update all the objects because the value of one field is not proper in the DB.
(In detail: A newly added date column contains "1/1/0001" in all rows, so on mapping, NHibernate replaces the date and, on tx.Commit(), updates every single row.)
[Edit: It turned out that this was wrong. Instead, these date fields were null but would be updated to 1/1/0001 by NHibernate. See Diego's answer for details.]
To prevent that, I found this post with an answer by Ben Scheirman as well as the blog comment referred to by the OP.
The commenter Christian says:
You can also disable automatic dirty checking and updating by disabling the snapshots in Hibernate with session.setReadOnly(o, true) or for all queried objects with query.setReadOnly(true).
(Note that this blog post is about Java Hibernate.)
query.SetReadOnly(true) was successful where I used queries. However, I also have code like this:
ISession session = this.NHibernateHelper.SessionFactory.OpenSession();
ITransaction tx = session.BeginTransaction();
try
{
BO resultBO = session.Get<BO>(id);
tx.Commit();
return resultBO;
}
catch (Exception ex)
{
tx.Rollback();
throw ex;
}
finally
{
session.Close();
}
In this case I don't have a query, and the said Session.SetReadOnly(resultBO, true) does not exist in NHibernate. Where has it gone?
I guess "evict" is basically not a good idea because it makes the object transient so I can't use it to update values in another session (at least it gets more complicated. I would also need to make sure all objects are always evicted so my generic update methods wouldn't need to differentiate between persistent and transient objects - or am I completely wrong?
Thanks and cheers,
chiccodoro
You are attacking the symptom instead of the disease.
What you have there is a ghost (see http://jfromaniello.blogspot.com/2010/02/nhibernate-ghostbuster-version-11.html)
Make the property nullable and you'll be fine.
Related
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 have the following code to create an in-memory SQLite DB for testing:
Configuration config = null;
FluentConfiguration fluentConfiguration = Fluently.Configure().Database(SQLiteConfiguration.Standard.InMemory().ShowSql()
).Mappings(m =>
{
m.FluentMappings.AddFromAssemblyOf<ReturnSourceMap>();
m.HbmMappings.AddFromAssemblyOf<ReturnSourceMap>();
m.FluentMappings.AddFromAssemblyOf<EchoTransaction>();
}).ExposeConfiguration(c => config = c);
ISessionFactory sessionFactory = fluentConfiguration.BuildSessionFactory();
_session = sessionFactory.OpenSession();
new SchemaExport(config).Execute(true, true, false, _session.Connection, Console.Out);
which seems to work fine for most things but unfortunately it is creating all the columns as not nullable.
For instance I have two classes:
InternalFund and ExternalFund. Both inherit from Fund and both persist to the same table.
ExternalFund has a column Manager_ID, InternalFund doesn't. Unfortunately this means that I can't persist an InternalFund as it throws a SQL Exception.
I don't need the referential integrity for my tests so would be happy if I could just make all columns nullable.
Does anyone know how to do this?
Thanks
Stu
You should try using the FluentNhibernate feature of Conventions. If you check out this link you will see the first example is of setting nullability as a default.
Oops, terribly sorry. It seems that the SQLite DB assumes nullability unless otherwise stated - unlike TSQL which requires it in the create statement.
In fact, I found hidden away in a sub-method that the particular property had a not null set on it in the mapping. Removing this sorted the problem.
Thanks for posting about conventions though, I'll have a look as I have another issue that they might sort.
Cheers
Stu
Ok, each and every time I get into this situation, I struggle back and forth until I find a way to solve it (and that is usually not the way I would have liked to solve it).
What I'm talking about is disconnected entities in EF that should update existing entities in the database.
I'll give an example of my problem here (this example is the last time I got into this problem that caused me to write this question).
I have a WCF service that uses Entity Framework as well. The other program that have added a service reference to my service have gotten proxy versions of the Entities as normal.
The case is that the consumer of the service now construct a object of this proxy class, and call the method UpdateEntity on the WCF service. This entity has a foreign key to another type of entities, and the primary key of the entity I want to link this new entity to is also sent as a parameter to this method. In this case, I want the entity with the same primary key in the database to be updated. It seems simple enough right?
My method looks something like this now:
public bool ChangeEntity(MyEntity entity, int otherTableForignKey)
{
//first I verify that the entity to update exist in the system
var entitytochange = entityContext.MyEntities.FirstOrDefault(e => e.Name == entity.Name);
if (systemtochange == null) return false;
try
{
entity.ForignEntity = entityContext.ForeignEntities.FirstOrDefault(f => f.Key == otherTableForignKey);
//code for updating the entity should go here, but I'm nor sure what
entityContext.SaveChanges();
return true;
}
catch (Exception exc)
{
return false;
}
}
I tried many different combinations of ApplyCurrentValues, Attach, setting ObjectState to Modified and so on, but I get either the error message that I can't add a new entity with the same key as an existing entity, that the object state of the new object can't be Added and so on.
So my question is: What is the best way to do this without writing code that looks like a big hack.
The only way I got this working now was to just set the properties of entitytochange manually with the properties of entity, but it is a bad solution since any added properties to MyEntity will break the code if I don't remember to add code in this method as well, and it seems there really should be another way that is better.
EDIT
When I put entityContext.MyEntities.ApplyCurrentValues(entity); where my comment is put above, I get the following exception on this line:
The existing object in the ObjectContext is in the Added state. Changes can only be applied when the existing object is in an unchanged or modified state.
However, if I remove this line above entity.ForignEntity = entityContext.ForeignEntities.FirstOrDefault(f => f.Key == otherTableForignKey); then the ApplyCurrentValues works without any problems.
Why would me setting the ForeignEntity of the object set it to Added state? So it seems that setting a Property on the Detached entity, attaches it to the context with a state of added?
I've got an Account model object and a UNIQUE constraint on the account's Name. In Domain Driven Design, using nHibernate, how should I check for the name's unicity before inserting or updating an entity?
I don't want to rely on a nHibernate exception to catch the error. I'd like to return a prettier error message to my user than the obscure could not execute batch command.[SQL: SQL not available]
In the question Where should I put a unique check in DDD?, someone suggested using a Specification like so.
Account accountA = _accountRepository.Get(123);
Account accountB = _accountRepository.Get(456);
accountA.Name = accountB.Name;
ISpecification<Account> spec = new Domain.Specifications.UniqueNameSpecification(_accountRepository);
if (spec.IsSatisfiedBy(accountObjA) == false) {
throw new Domain.UnicityException("A duplicate Account name was found");
}
with the Specification code as:
public bool IsSatisfiedBy(Account obj)
{
Account other = _accountRepository.GetAccountByName(obj.Name);
return (other == null);
}
This works for inserts, but not when doing an update because. I tried changing the code to:
public bool IsSatisfiedBy(Account obj)
{
Account other = _accountRepository.GetAccountByName(obj.Name);
if (obj == null) { // nothing in DB
return true;
}
else { // must be the same object.
return other.Equals(obj);
}
}
The problem is that nHibernate will issue an update to the database when it executes GetAccountByName() to recover a possible duplicate...
return session.QueryOver<Account>().Where(x => x.Name == accntName).SingleOrDefault();
So, what should I do? Is the Specification not the right way to do it?
Thanks for your thoughts!
I'm not a fan of the specification pattern for data access, it always seems like jumping hoops to get anything done.
However, what you've suggested, which really just boils down to:
Check if it already exists.
Add if it doesn't; Show user-friendly message if it does.
... is pretty much the easiest way to get it done.
Relying on database exceptions is the other way of doing it, if your database and it's .NET client gracefully propagates the table & column(s) that were infringing the unique constraint. I believe most drivers don't do so (??), as they just throw a generic ConstraintException that says "Constraint XYZ was violated on table ABC". You can of course have a convention on your unique constraint naming to say something like UK_MyTable_MyColumn and do string magic to pull the table & column names out.
NHibernate has a ISQLExceptionConverter that you can plug into the Configuration object when you set NHibernate up. Inside this, you get exposed to the exception from the .NET data client. You can use that exception to extract the table & columns (using the constraint name perhaps?) and throw a new Exception with a user friendly message.
Using the database exception way is more performant and you can push a lot of the detecting-unique-constraint-violation code to the infrastructure layer, as opposed to handling each one case by case.
Another thing worth pointing out with the query-first-then-add method is that to be completely transaction safe, you need to escalate the transaction level to serializable (which gives the worst concurrency) to be totally bullet proof. Whether you need to be totally bullet proof or not, depends on your application needs.
You need to handle it with Session.FlushMode mode to set to FlushMode.Commit and use transaction to rollback if at all update fired.
With my only ORM knowledge being L2S/EF, I was surprised when the following code inserted a row into the database before I called repo.Save:
var repo = new UserRepository();
var user = new User { Name = "test" }
repo.Add(user);
//repo.Save();
Repo looks like this:
public void Add(T entity)
{
session.Save(entity);
}
public void Save()
{
session.Flush();
}
After some digging, it seems NHibernate needs to make the insert happen right away in order to get the ID of the new entity (since it's using an auto increment ID). But L2S/EF doesn't work like this; I can add many entities and save them all at the end.
Question is: is there a way to achieve the same thing with NHibernate, while still using auto increment IDs, and out of interest does anyone know why it works like this?
Fabio Maulo already blogged about the usage of identity generator a few times. The answer is: use hilo, guid.comb or something like this.
NHibernate needs the identity because every entity in the session (they are called "persistent entities") needs to be identified. The identity is also normally used to determine if the record already exists in the database (unsaved value).
session.Save actually only makes a transient entity persistent. When the database is generating the id, it needs to be stored to get the id. If NH can create the id itself (eg using hilo), it could be stored next time when the session gets flushed.