I'm receiving on my controller some int which is parameter I'm using for getting entity.
This entity have List Collection which I need to load together with my entity.
I cannot access Fetch method in session.Get so I dont know how to achive.
When in my view I tried to access to my collection like entity.Collection it throws an error, no session or session was closed
Here is my code
public ActionResult Details(int id)
{
MyDomain.Property data = null;
using (//open session)
{
using (//using transaction)
{
data = session.Get<MyDomain.Property>(id);
//I need to load Photo() collection.
transaction.Commit();
}
}
return PartialView("DetailsPartial", data);
}
Your entity has a collection's property with a proxy (not real collection). When you close session you can't use lazy load, so, you need to get real collection objects.
You should get it with query:
Session.QueryOver<Entity>()
.Where(entity => entity.Id == id)
.Fetch(entity => entity.CollectionProperty).Eager
.SingleOrDefault<Entity>();
Related
Before I go creating my own SQL scripts by hand for this, I have a scenario where I want to get the ids of a foreign key, but not the entirety of the foreign entities, using EF Core.
Right now, I'm getting the ids manually by looping through the related entities and extracting the ids one at a time, like so:
List<int> ClientIds = new List<int>();
for (var i = 0; i < Clients.length; i++){
ClientIds.add(Clients.ElementAt(i).Id);
}
To my understanding, this will either cause data returns much larger than needed (my entity + every related entity) or a completely separate query to be run for each related entity I access, which obviously I don't want to do if I can avoid it.
Is there a straightforward way to accomplish this in EF Core, or do I need to head over the SQL side and handle it myself?
Model:
public class UserViewModel {
public UserViewModel(UserModel userModel){
ClientIds = new List<int>();
for (var i = 0; i < UserModel.Clients.length; i++){
ClientIds.add(Clients.ElementAt(i).Id);
}
//...all the other class asignments
}
public IEnumerable<int> ClientIds {get;set;}
//...all the other irrelevant properties
}
Basically, I need my front-end to know which Client to ask for later.
It looks like you are trying to query this from within the parent entity. I.e.
public class Parent
{
public virtual ICollection<Client> Clients { get; set; }
public void SomeMethod()
{
// ...
List<int> ClientIds = new List<int>();
for (var i = 0; i < Clients.length; i++)
{
ClientIds.add(Clients.ElementAt(i).Id);
}
// ...
}
}
This is not ideal because unless your Clients were eager loaded when the Parent was loaded, this would trigger a lazy load to load all of the Clients data when all you want is the IDs. Still, it's not terrible as it would only result in one DB call to load the clients.
If they are already loaded, there is a more succinct way to get the IDs:
List<int> ClientIds = Clients.Select(x => x.Id).ToList();
Otherwise, if you have business logic involving the Parent and Clients where-by you want to be more selective about when and how the data is loaded, it is better to leave the entity definition to just represent the data state and basic rules/logic about the data, and move selective business logic outside of the entity into a business logic container that scopes the DbContext and queries against the entities to fetch what it needs.
For instance, if the calling code went and did this:
var parent = _context.Parents.Single(x => x.ParentId == parentId);
parent.SomeMethod(); // which resulted in checking the Client IDs...
The simplest way to avoid the extra DB call is to ensure the related entities are eager loaded.
var parent = _context.Parents
.Include(x => x.Clients)
.Single(x => x.ParentId == parentId);
parent.SomeMethod(); // which resulted in checking the Client IDs...
The problem with this approach is that it will still load all details about all of the Clients, and you end up in a situation where you end up defaulting to eager loading everything all of the time because the code might call something like that SomeMethod() which expects to find related entity details. This is the use-case for leveraging lazy loading, but that does have the performance overheads of the ad-hoc DB hits and ensuring that the entity's DbContext is always available to perform the read if necessary.
Instead, if you move the logic out of the entity and into the caller or another container that can take the relevant details, so that this caller projects down the data it will need from the entities in an efficient query:
var parentDetails = _context.Parents
.Where(x => x.ParentId == parentId)
.Select(x => new
{
x.ParentId,
// other details from parent or related entities...
ClientIds = x.Clients.Select(c => c.Id).ToList()
}).Single();
// Do logic that SomeMethod() would have done here, or pass these
// loaded details to a method / service to do the work rather than
// embedding it in the Entity.
This doesn't load a Parent entity, but rather executes a query to load just the details about the parent and related entities that we need. In this example it is projected into an anonymous type to hold the information we can later consume, but if you are querying the data to send to a view then you can project it directly into a view model or DTO class to serialize and send.
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 have a very strange issue that I cannot explain. I have my base mapping with this
//This will automatically cast the row into the correct object type based on the value in AccountType
DiscriminateSubClassesOnColumn<string>("AccountType")
.Formula(String.Format("CASE AccountType WHEN {0} THEN '{1}' WHEN {2} THEN '{3}' ELSE '{4}' END",
(int)PaymentMethodType.CheckingAccount,
typeof(ACH).Name,
(int)PaymentMethodType.SavingsAccount,
typeof(ACH).Name,
typeof(CreditCard).Name));
I have looked in the logs, I have executed the sql that nhibernate is generating, and all records have the same data. There is not difference in them that would denote why this should not work.
The base class is PaymentMethodBase. I have 2 subclasses, CreditCard and ACH, which inherit from PaymentMethodBase.
Then, I have this extension
public static string PaymentMethodName(this PaymentMethodBase paymentMethod)
{
if (paymentMethod is ACH)
{
var ach = (ACH)paymentMethod;
return String.Format("{0} {1}", ach.BankName, String.Format("XXXX{0}", ach.AccountNumber.Substring(ach.AccountNumber.Length - 4)));
}
if (paymentMethod is CreditCard)
{
var creditCard = (CreditCard)paymentMethod;
return String.Format("{0} {1}", creditCard.Name, creditCard.CreditCardNumber);
}
return "Unknown Payment Method";
}
Which I call like this.
public SelectList PaymentMethodsSelectList
{
get
{
var methods = (from p in PaymentMethods
where p != null
select new
{
id = p.PaymentMethodId,
name = p.PaymentMethodName()
}).OrderBy(x => x.name);
var results = methods.ToList();
results.Insert(0, new { id = (int)NewPaymentMethods.ACH, name = "<New eCheck Account...>" });
results.Insert(0, new { id = (int)NewPaymentMethods.CreditCard, name = "<New Credit Card...>" });
return new SelectList(results, "id", "name");
}
}
This code is used by 2 models. The collection of payment methods are all coming from the same object - a customer object. The collection is mapped like this.
HasMany<PaymentMethodBase>(x => x.PaymentMethods)
.KeyColumn("CustomerId")
.Where(y => y.AccountType < 10)
.Inverse()
.Cascade.All();
So, I get the customer 2 different ways. One is that I get the customer through another object (main site). The other has the object being pulled directly by id (in an iframe). The direct by id method works every time. The other method, where I get the customer through another object, causes only the first and last payment method to cast correctly. If there are more than 2, they are left in the base class and appear in the middle of the list after the sort.
I have tried changing the parent object to just mapping the id and then getting the customer record by the ID. Failure. There is something else in the way that is causing this to happen, but only on that one model.
I suspect that the issue here is Fetching issue.
Since the extension method is running on the .Net side rather than in the "NHibernate level" it cannot run properly when the collection of payment methods is not available.
Perhaps in the direct by Id methos you have Fetching set up for the payments whereas in the indirect method the automatic fetching goes only to the Customer object but stops short before fetching the Payment methods.
Try to instruct NHibernate to pre-fetch the Payment methods for you in the indirect method.
Something like:
Session.Query<SomeObject>.Where(.....).Fetch(x => x.Customer).ThenFetch(c => c.PaymentMethods)
The problem here appeared to be the usage of extension methods within a linq statement to return a value based on the type. The issue is that it would work some places but not others, probably due to some fetching issue, as suggested by Variant.
I solved this problem by making a property in my base class like this
public virtual string DisplayName { get { return "Unknown"; } }
Then I overrode the property in my child class and added the logic that was in the extension method for that type.
public override string DisplayName { get { return String.Format("{0} {1}", Name, AccountMask); } }
When calling Index method on FullTextSession with plain poco object throws the error below, works fine with proxied object.
Stacktrace:
[TransientObjectException: the instance was not associated with this session]
NHibernate.Impl.SessionImpl.GetIdentifier(Object obj) +500
I'm trying to squeeze the performance out of the nhibernate select method I've got the following code:
public virtual IList<T> LoadSearch()
{
return Adapater.Session.QueryOver<T>()
.SelectList(e =>
{
e.Select(x => x.Id);
e.Select(x => x.Title);
e.Select(x => x.Description);
return e;
}).List<object[]>()
.Select(props => new T
{
Id = (Guid)props[0],
Title = (string)props[1],
Description = (string)props[2]
}).ToList();
}
Is there way to return a proxied result? or some how adapt the list to a proxied list?
I think you can only index objects that are associated with a session, i.e. proxied entities.
The plain POCOs you are returning didn't come from NH - so aren't associated with a NH session.
You could try using ISession.Lock(instance, NHibernate.LockMode.None); on each entity to associate it with the session, but I really don't know if that'd work.
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.