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?
Related
I want to delete a record from the DB that hasn't been retrieved from a breeze query. The entity hasn't been retrieved so it's not in the cache, but I know the KEY of the record from another operation. Here's what I've tried:
create a new entity from the manager:
manager.createEntity(entityNames.book);
setting the ID :
bookToDelete().bookID(1); // bookToDelete is a ko observable from step 1
updating the state:
bookToDelete().entityAspect.setDeleted();
When I save changes, this transaction is not included in the JSON
You almost have it. Calling entityAspect.setDeleted on an 'Added' entity moves it directly to a 'Detached' state, which in effect removes it from the EntityManager, and hence it cannot be saved. This is deliberate. It handles the case where you create an entity and later delete it. In this case, there is no entity to save.
So, in your case, you have to make the entity either 'Modified' or 'Unchanged' before you call entityAspect.setDeleted. You can do this by either calling entityAspect.setUnchanged or entityAspect.setModified before calling entityAspect.setDeleted or you can call entityAspect.acceptChanges.
Note that you will also have to insure that the 'clone' entity passes validation and if you have a concurrency field on the entity, you will need to set this appropriately as well.
UPDATE Dec 7th
You can create the book entity in the marked-for-delete state in a single step as shown:
var book = manager.createEntity(entityNames.book,
{ BookID: 1 }, // use initializer to set the key
breeze.EntityState.Deleted); // creates the entity in the Deleted state
Be sure to initialize it with all other properties that are necessary for the entity to pass validation and optimistic concurrency checks on the server.
No problem if you don't have these checks. Not sure how you'd get those values without querying the server if you did have such checks.
got it. cant delete entity while still in added state. I first setModified. then setdeleted. didnt see any side affects.
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've been banging my head off what should be a simple issue. I'm trying to do the following basic operation
1) Check if entity exists by a field other than ID
2) If not, create entity
Problem is this is in a console app that is multi-threaded, so I need to somehow get an entity by a field other than the ID and set the LockMode to Upgrade (or at least I think thats what needs to be done). From what I see there is no way to do that with ISession.
Any ideas?
in a single process use a global lockobject
lock(existsLocker)
{
var entity = session.Query<Entity>().Where(...).FirstOrDefault();
if (entity == null)
{
entity = new Entity();
session.Save(entity);
session.Flush();
}
}
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.
I'm developing a WCF Data Service with self tracking entities and I want to prevent clients from inserting duplicated content. Whenever they POST data without providing a value for the data key, I have to execute some logic to determine whether that data is already present inside my database or not. I've written a Change interceptor like this:
[ChangeInterceptor("MyEntity")]
public void OnChangeEntity(MyEntity item, UpdateOperations operations){
if (operations == UpdateOperations.Add)
{
// Here I search the database to see if a matching record exists.
// If a record is found, I'd like to use its ID and basically change an insertion
// into an update.
item.EntityID = existingEntityID;
item.MarkAsModified();
}
}
However, this is not working. The existingEntityID is ignored and, as a result, the record is always inserted, never updated. Is it even possible to do? Thanks in advance.
Hooray! I managed to do it.
item.EntityID = existingEntityID;
this.CurrentDataSource.ObjectStateManager.ChangeObjectState(item, EntityState.Modified);
I had to change the object state elsewhere, ie. by calling .ChangeObjectState of the ObjectStateManager, which is a property of the underlying EntityContext. I was mislead by the .MarkAsModified() method which, at this point, I'm not sure what it does.