I am looking for a simple NHibernate example which will show me how iterate on an entire table. Here is what I have so far, but it is not working. I am getting an "System.InvalidOperationException: Operation is not valid due to the current state of the object.". What am I doing wrong?
public IEnumerable<EMPDATA> getEMPData()
{
using (ISession session = NHibernateHelper.OpenSession())
{
IEnumerable<EMPDATA> empData = session.CreateQuery("from EMPDATA").Enumerable<EMPDATA>();
return empData;
}
}
public static void Main(System.String[] args)
{
log.Debug("Entered main");
Console.WriteLine("Entered main");
try
{
IEMPDataRepository repository = new EMPDataRepository();
IEnumerable<EMPDATA> iterList = repository.getEMPData();
while( iterList.GetEnumerator().MoveNext())
{
EMPDATA emp = iterList.GetEnumerator().Current;
log.Debug(emp.EMP_ID);
}
}
catch (System.Exception ex)
{
log.Error("Exception occured reading emp data", ex);
}
Here is my mapping:
You request an Enumerable result, which probably relies on the session still beeing open.
since you Dispose the session after returning the Enumerable instance, you have closed the connection to the database.
EDIT: see NotSupportedException on IQuery's Enumerable when using statelesssession
Short answer: use .List instead of .Enumerable.
Longer answer:
1. I agree with Phill- looks like a job for a SP
2. Diego is (obviously) right, but if I were you i'd use SetFirstResult() and SetMaxResult() in order to control the amount of data you load into memory in each iteration (don't forget to sort by something when using this method, of course).
Related
I have a scenario similar to this:
Asp.NET MVC 4 website using nHibernate Session Per Request.
The session is injected using Ninject onto a Repository with the Get and Save methods.
There are a lot of articles talking about Session Per Request and saying that is the way to do things on a web application.
But i'm having problems implementing logic like this one:
Read Data From Database
Alter Entity information
Save to Database
Read another entity
Alter entity
Save ... but an EXCEPTION OCCURS
I want to show my view with a message to the user. But i have also to refresh the resulting web page,
so i have also to read some information from the database.
According to nHibernate documentation, the session with the exception must be discarded Documentation Here
But i can't find any articles about the best way to proceed here.
What's the best approach for this situation?. I will have to inject a new Session to my repository object?.
Thanks.
You can create a new session from the SessionFactory property of the original session. You can access the original session object by either exposing it in the repository class or injecting it into the controller. Then you can create a new repository with the new session.
I do this in some of my Actions where I expect unique key violations to occur and I have to reload lookup data in the model. Here's an example:
public ActionResult Create(MeasuresEditView model)
{
if (ModelState.IsValid)
{
using (var txn = _session.BeginTransaction())
{
try
{
var measure = new Measure { Code = model.Code };
_session.Save(measure);
txn.Commit();
return RedirectToAction("Index");
}
catch (UniqueKeyException)
{
txn.Rollback();
var msg = string.Format("A measure with the code '{0}' already exists, please enter a different code or cancel.", model.Code);
ModelState.AddModelError("Code", msg);
}
catch (Exception ex)
{
if (txn.IsActive)
{
txn.Rollback();
}
log.Error("Create", ex);
throw;
}
}
}
// have to rebuild selectlist on post in new txn in case it was rolled back
using (var session = _session.SessionFactory.OpenSession())
using (var txn = session.BeginTransaction())
{
SetProductGroupSelectList(session, model, manualId);
txn.Commit();
}
return View(model);
}
I am trying to write a test for my NHibernate mappings that will automatically pick up and test any new mappings that get added.
At the moment I have a test that opens a session to a known test database then attempts to load the first entity of each type and asserts that it is not null.
This all works fine but it means that every time I add a new entity mapping, I need to remember to update the test.
So, what I want to do is to inspect the mappings and try to load one of each of the mapped entities, but the NHibernate Configuration object that the sessionfactory is built from is not visible to my test so I was wondering if there is a way to access a list of mapped entities from the session or do I need to expose the original Configuration instead?
You can get SessionFactory from Session and SessionFactory has method GetAllClassMetadata() which returns list of IClassMetadata. And from IClassMetadata you can get MappedClass (GetMappedClass())
But you will need some extra work to get subclasses. This code can help:
var metaData = this.session.SessionFactory.GetClassMetadata(baseClass);
if (metaData != null && metaData.HasSubclasses)
{
foreach (string entityName in ((NHibernate.Persister.Entity.IEntityPersister)metaData).EntityMetamodel.SubclassEntityNames)
{
var metadata = this.session.SessionFactory.GetClassMetadata(entityName);
result.Add(metadata.GetMappedClass(EntityMode.Poco));
}
}
I expose the configuration object and do a mapping that queries all of my entities like this. It will output all errors from each of my mappings.:
[TestMethod()]
public void AllNHibernateMappingsAreOkay()
{
bool failed = false;
log4net.Config.XmlConfigurator.Configure();
using (ISession session = SessionFactory.GetCurrentSession())
{
foreach (var s in SessionFactory.GetConfig().ClassMappings)
{
try
{
SessionFactory.GetCurrentSession().CreateQuery(string.Format("from {0} e", s.MappedClass.Name))
.SetFirstResult(0).SetMaxResults(50).List();
}
catch (Exception ex)
{
failed = true;
log.ErrorFormat("\r\n\r\n {0} \r\n {1} \r\n\r\n", ex.Message, ex.InnerException.Message);
}
}
}
Assert.IsFalse(failed, "One or more mappings have errors in them. Please refer to output or logs.");
}
if you have only one row per entity then you could issue session.QueryOver<object>().List();
I am trying to find the perfect way to handle this exception and force client changes to overwrite any other changes that caused the conflict. The approach that I came up with is to wrap the call to Session.Transaction.Commit() in a loop, inside the loop I would do a try-catch block and handle each stale object individually by copying its properties, except row-version property then refreshing the object to get latest DB data then recopying original values to the refreshed object and then doing a merge. Once I loop I will commit and if any other StaleObjectStateException take place then the same applies. The loop keeps looping until all conflicts are resolved.
This method is part of a UnitOfWork class. To make it clearer I'll post my code:
// 'Client-wins' rules, any conflicts found will always cause client changes to
// overwrite anything else.
public void CommitAndRefresh() {
bool saveFailed;
do {
try {
_session.Transaction.Commit();
_session.BeginTransaction();
saveFailed = false;
} catch (StaleObjectStateException ex) {
saveFailed = true;
// Get the staled object with client changes
var staleObject = _session.Get(ex.EntityName, ex.Identifier);
// Extract the row-version property name
IClassMetadata meta = _sessionFactory.GetClassMetadata(ex.EntityName);
string rowVersionPropertyName = meta.PropertyNames[meta.VersionProperty] as string;
// Store all property values from client changes
var propertyValues = new Dictionary<string, object>();
var publicProperties = staleObject.GetType().GetProperties();
foreach (var p in publicProperties) {
if (p.Name != rowVersionPropertyName) {
propertyValues.Add(p.Name, p.GetValue(staleObject, null));
}
}
// Get latest data for staled object from the database
_session.Refresh(staleObject);
// Update the data with the original client changes except for row-version
foreach (var p in publicProperties) {
if (p.Name != rowVersionPropertyName) {
p.SetValue(staleObject, propertyValues[p.Name], null);
}
}
// Merge
_session.Merge(staleObject);
}
} while (saveFailed);
}
The above code works fine and handle concurrency with the client-wins rule. However, I was wondering if there is any built-in capabilities in NHibernate to do this for me or if there is a better way to handle this.
Thanks in advance,
What you're describing is a lack of concurrency checking. If you don't use a concurrency strategy (optimistic-lock, version or pessimistic), StaleStateObjectException will not be thrown and the update will be issued.
Okay, now I understand your use case. One important point is that the ISession should be discarded after an exception is thrown. You can use ISession.Merge to merge changes between a detached a persistent object rather than doing it yourself. Unfortunately, Merge does not cascade to child objects so you still need to walk the object graph yourself. So the implementation would look something like:
catch (StaleObjectStateException ex)
{
if (isPowerUser)
{
var newSession = GetSession();
// Merge will automatically get first
newSession.Merge(staleObject);
newSession.Flush();
}
}
The entities and mappings I'm talking about in this question can be found here :)
Here is the context:
I have a parent view-model which helps to manage some entities, and which has its own session.
From this VM, I open another view-model (with its own session too), do some changements to the entity (add and/or remove children), and when I validate the changements, I commit the session and warns the first view-model to refresh the display:
public void Validate()
{
using (var tx = Session.BeginTransaction())
{
try
{
SelectedTeam.ClearRoster();
foreach (var teamPlayer in TeamPlayers)
SelectedTeam.AddPlayer(teamPlayer);
teamsRepository.SaveOrUpdate(SelectedTeam);
tx.Commit();
}
catch (Exception ex)
{
tx.Rollback();
}
finally
{
if (tx.WasCommitted)
ServiceLocator.Current.GetInstance<Mediator>().NotifyColleagues(MediatorMessages.DisplayEntityInfos, SelectedTeam.Id);
}
}
}
Here is the faulted method of the parent VM:
public void RefreshEntitiesListAndDisplayEntityInfos(int selectedEntityId)
{
TEntity entity = entitiesRepository.Load(selectedEntityId);
Session.Refresh(entity);
//...
}
The exception is thrown at the Refresh line:
NHibernate.UnresolvableObjectException
And the message is:
No row with the given identifier exists[Emidee.CommonEntities.PlayerInTeam#3
I can open and change the entity multiple times, but it seems that the exception is thrown when I delete a children, then add another one, and finally delete another one.
After some readings on the web, it seems that's because when I refresh the entity, and because I changed the HasMany relationship (because I have deleted a player for example), NH tries to reload the deleted row.
I've tried to add a NotFound.Ignore statement on the HasMany in my mappings, I've tried to force a new query to the DB instead of a Load, but I still get this exception.
Does someone know how I could fix that?
Thanks in advance
Mike
This is a known behavior when refreshing objects with modified collections.
To force reload, change your method to do session.Evict with the entity as a parameter. This is the code we use in our base model class:
public T ReGet<T>(T entity) where T : IEntity
{
var id = entity.Id;
Session.Evict(entity);
return Session.Get<T>(id);
}
Well, I've just spotted the problem.
To update the players list of the team, I used to clear the list, and add the new players, before updating the entity.
Now, I update the list by removing and adding only the players who have been moved by the user, and I don't have any problems at all now.
That's weird. I don't know what was wrong before, but as least that works now.
Ayende has an article about how to implement a simple audit trail for NHibernate (here) using event handlers.
Unfortunately, as can be seen in the comments, his implementation causes the following exception to be thrown: collection xxx was not processed by flush()
The problem appears to be the implicit call to ToString on the dirty properties, which can cause trouble if the dirty property is also a mapped entity.
I have tried my hardest to build a working implementation but with no luck.
Does anyone know of a working solution?
I was able to solve the same problem using following workaround: set the processed flag to true on all collections in the current persistence context within the listener
public void OnPostUpdate(PostUpdateEvent postEvent)
{
if (IsAuditable(postEvent.Entity))
{
//skip application specific code
foreach (var collection in postEvent.Session.PersistenceContext.CollectionEntries.Values)
{
var collectionEntry = collection as CollectionEntry;
collectionEntry.IsProcessed = true;
}
//var session = postEvent.Session.GetSession(EntityMode.Poco);
//session.Save(auditTrailEntry);
//session.Flush();
}
}
Hope this helps.
The fix should be the following. Create a new event listener class and derive it from NHibernate.Event.Default.DefaultFlushEventListener:
[Serializable]
public class FixedDefaultFlushEventListener: DefaultFlushEventListener
{
private static readonly log4net.ILog log = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
protected override void PerformExecutions(IEventSource session)
{
if (log.IsDebugEnabled)
{
log.Debug("executing flush");
}
try
{
session.ConnectionManager.FlushBeginning();
session.PersistenceContext.Flushing = true;
session.ActionQueue.PrepareActions();
session.ActionQueue.ExecuteActions();
}
catch (HibernateException exception)
{
if (log.IsErrorEnabled)
{
log.Error("Could not synchronize database state with session", exception);
}
throw;
}
finally
{
session.PersistenceContext.Flushing = false;
session.ConnectionManager.FlushEnding();
}
}
}
Register it during NHibernate configuraiton:
cfg.EventListeners.FlushEventListeners = new IFlushEventListener[] { new FixedDefaultFlushEventListener() };
You can read more about this bug in Hibernate JIRA:
https://hibernate.onjira.com/browse/HHH-2763
The next release of NHibernate should include that fix either.
This is not easy at all. I wrote something like this, but it is very specific to our needs and not trivial.
Some additional hints:
You can test if references are loaded using
NHibernateUtil.IsInitialized(entity)
or
NHibernateUtil.IsPropertyInitialized(entity, propertyName)
You can cast collections to the IPersistentCollection. I implemented an IInterceptor where I get the NHibernate Type of each property, I don't know where you can get this when using events:
if (nhtype.IsCollectionType)
{
var collection = previousValue as NHibernate.Collection.IPersistentCollection;
if (collection != null)
{
// just skip uninitialized collections
if (!collection.WasInitialized)
{
// skip
}
else
{
// read collections previous values
previousValue = collection.StoredSnapshot;
}
}
}
When you get the update event from NHibernate, the instance is initialized. You can safely access properties of primitive types. When you want to use ToString, make sure that your ToString implementation doesn't access any referenced entities nor any collections.
You may use NHibernate meta-data to find out if a type is mapped as an entity or not. This could be useful to navigate in your object model. When you reference another entity, you will get additional update events on this when it changed.
I was able to determine that this error is thrown when application code loads a Lazy Propery where the Entity has a collection.
My first attempt involed watching for new CollectionEntries (which I've never want to process as there shouldn't actually be any changes). Then mark them as IsProcessed = true so they wouldn't cause problems.
var collections = args.Session.PersistenceContext.CollectionEntries;
var collectionKeys = args.Session.PersistenceContext.CollectionEntries.Keys;
var roundCollectionKeys = collectionKeys.Cast<object>().ToList();
var collectionValuesClount = collectionKeys.Count;
// Application code that that loads a Lazy propery where the Entity has a collection
var postCollectionKeys = collectionKeys.Cast<object>().ToList();
var newLength = postCollectionKeys.Count;
if (newLength != collectionValuesClount) {
foreach (var newKey in postCollectionKeys.Except(roundCollectionKeys)) {
var collectionEntry = (CollectionEntry)collections[newKey];
collectionEntry.IsProcessed = true;
}
}
However this didn't entirly solve the issue. In some cases I'd still get the exception.
When OnPostUpdate is called the values in the CollectionEntries dictionary should all already be set to IsProcessed = true. So I decided to do an extra check to see if the collections not processed matched what I expected.
var valuesNotProcessed = collections.Values.Cast<CollectionEntry>().Where(x => !x.IsProcessed).ToList();
if (valuesNotProcessed.Any()) {
// Assert: valuesNotProcessed.Count() == (newLength - collectionValuesClount)
}
In the cases that my first attempt fixed these numbers would match exactly. However in the cases where it didn't work there were extra items alreay in the dictionary. In my I could be sure these extra items also wouldn't result in updates so I could just set IsProcessed = true for all the valuesNotProcessed.