Develop Reference

Generate and auto increment the Id in Entity Framework database first

I have a table CampaignLanguage. The primary key is Id. It should be auto increment.
So I have the code:
public partial class CampaignLanguage
{
public CampaignLanguage()
{
this.CampaignLanguageQuestions = new HashSet<CampaignLanguageQuestion>();
}
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int Id { get; set; }
Then in the controller, I want to save the generated object.
[HttpPost]
public ActionResult Save(int clientId, int campaignId)
{
var campaign = CampaignService.GetCampaignById(campaignId);
var campaignLanguage = campaign.CampaignLanguages.Where(x => x.CampaignId == campaignId).FirstOrDefault();
if (campaignLanguage != null)
{
campaignLanguage.WelcomeMessage = message;
CampaignService.Save(campaignLanguage);
}
else
{
campaignLanguage = new CampaignLanguage();
campaignLanguage.Id = 1;
CampaignService.Save(campaignLanguage);
}
return Redirect("/Campaign/Index/" + clientId);
}
However, I get the error.
{"Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries."}
I don't want to change my CampaignService.Save method. So how to fix it?
EDIT
public void Save(CampaignLanguage campaignLanguage)
{
_campaignLanguageRepository.Update(campaignLanguage);
_unitOfWork.Commit();
}
EDIT 1
public virtual void Add(T entity)
{
dbset.Add(entity);
}
public virtual void Update(T entity)
{
dbset.Attach(entity);
dataContext.Entry(entity).State = EntityState.Modified;
}

You should be calling Add instead of Update as this is a new instance you want to insert into the data store. Your Save method should check if the primary (auto incremented key) has a value greater than 0 to see if it is new or not. Alternatively you can also see if it is already attached. There is also no need to call Update, setting the entity to state modified does nothing except ensure that all properties will be written back to the DB but the DbContext implements change tracking on entities so this will already happen (unless you are working in a detached state).
public void Save(CampaignLanguage campaignLanguage)
{
if(campaignLanguage.Id == 0)
_campaignLanguageRepository.Add(campaignLanguage);
else
_campaignLanguageRepository.Update(campaignLanguage);
_unitOfWork.Commit();
}
On a side note: The type DbContext already implements a Unit of Work pattern and DbSet<T> is an implementation of a Repository pattern. There should not be any need to add another customer Unit of work and repository pattern around EF, you are just creating a whole abstraction layer for no reason that will problems with readability as well as issues later when you want to perform more complex operations like joining multiple tables together in a query.

Unfortunately, you need to change your CampaignService.Save. You are trying to update an inexistent campaignLanguage object.
The other problem is you are trying to force a key into an Identity column. You cannot do it with out first set insert_identy to the table.
Maybe, you need to ask for the correct method of CampaignService.

Updating an Entity in EF with a 1:1 relationship

I have an application with 4 layers:
-Core (Models)
-Repository (EF DbContext actions)
-Service (Business logic)
-Web (MVC)
I'm trying to update an object with a 1:1 relationship with EF using the following method:
public async Task<bool> UpdateProductTicketing(ProductTicketing ticketing)
{
var product = await GetProductByIdAsync(ticketing.ProductId);
// Validation removed for simplicity
// 'ticketing' passed validation so let's
// just replace it with the existing record.
product.Ticketing = ticketing;
_repo.ProductRepository.Update(product);
return await _repo.SaveAsync();
}
This works for an initial insert, but it doesn't work as I'd expect when I'm updating the record:
A first chance exception of type 'System.Data.Entity.Infrastructure.DbUpdateException' occurred...
The actual error message is:
Violation of PRIMARY KEY constraint 'PK_dbo.ProductTicketing'. Cannot insert duplicate key in object 'dbo.ProductTicketing'. The statement has been terminated.
Obviously the PK and FK "ProductId" doesn't change - so why does EF try to drop and insert my record instead of just updating it, and why does it fail?
But more importantly - how can I prevent this. I know I can manually map the object values and then update it - that works but it's tedious mapping two identical objects together and doesn't feel correct.
My repository for retrieving the Product object is in my Repository layer, while the method above is in my Service layer.
This is how I'm currently resolving this - and it looks as dirty as it feels:
public async Task<bool> UpdateProductTicketing(ProductTicketing ticketing)
{
var product = await GetProductByIdAsync(ticketing.ProductId);
// Validation removed for simplicity
if (product.Ticketing == null)
{
product.Ticketing = ticketing;
}
else
{
product.Ticketing.AllowEventBooking = ticketing.AllowEventBooking;
// Doing the same for all other properties etc
// etc
// etc
}
_repo.ProductRepository.Update(product);
return await _repo.SaveAsync();
}
How can I achieve this without doing all this horrible mapping an object to an identical object?
Edit
Here are the two models referred to above:
[Table(#"Products")]
public class Product
{
[Key]
public int Id { get; set; }
public virtual ProductTicketing Ticketing { get; set; }
// Removed others for clarity
[Timestamp]
public byte[] RowVersion { get; set; }
}
[Table(#"ProductTicketing")]
public class ProductTicketing
{
[Key, ForeignKey("Product")]
public int ProductId { get; set; }
public bool AllowEventBooking { get; set; }
// Removed others for clarity
public virtual Product Product { get; set; }
}
It's also probably worth noting that the "ProductTicketing" object I'm passing into the UpdateProductTicketing method is a new object created from values in my controller - but the ID is the same so I assume it should work.

I think I see the problem now - when you do product.Ticketing = ticketing;, EF treats this as a new insert.
To avoid this, you can do one of these things:
Continue using the workaround (which is not a wokaround actually but just the way EF expects you to tell when to insert vs. when to update).
Now this depends on rest of your code and design, but instead of fetching the product, you can fetch the ticket and update its properties. Of course, this means that if the ticketing is not found, you need to insert it which then kinda looks like what you're already doing with UpdateProductTicketing.
Use the InsertOrUpdate pattern (I made some assumptions about your code but hopefully it gives you the idea - the main thing here is the InsertOrUpdate method):
public class ProductRepository : IRepository
{
private SomeContext context;
public void InsertOrUpdate(ProductTicketing ticketing)
{
context.Entry(ticketing).State = ticketing.ProductId == 0 ?
EntityState.Added :
EntityState.Modified;
context.SaveChanges();
}
}
// And a generic version
public void InsertOrUpdate<T>(T entity) where T : class
{
if (context.Entry(entity).State == EntityState.Detached)
context.Set<T>().Add(entity);
context.SaveChanges();
}

You are getting that error because ef thinks that the ProductTicket is a new entity and is trying to insert the entity into the db. I don't know about the _repo.ProductRepository.Update(product) call but how about you attach the ProductTicket to the context and set the entity state to modified

NHibernate: Generate Custom Primary Key in OnPreInsert

In my OData service I have to create a custom primary key in the OnPreInsert event handler.
I know I can't use #event.Id to assign the key because it doesn't expose the setter property.
I used the reflection to set the value of this property as shown below:
public bool OnPreInsert(PreInsertEvent #event)
{
if(#event.Entity is MyEnity)
{
var myEntity = #event.Entity as MyEnity;
string newKey = GetCustomKey(...);
myEntity.myId = newKey;
var property = typeof(AbstractPreDatabaseOperationEvent).GetProperty("Id");
if (property != null)
{
property.SetValue(#event,newKey);
}
}
return false;
}
During the debug mode I can see that the value of #event.Id is initialized properly, however the key saved in the database is not the one I generated in the OnPreInsert event handler.
What am I doing wrong here?

Please, try to check this recent Q&A:
NHibernate IPreUpdateEventListener, IPreInsertEventListener not saving to DB
The point is, that as described here:
NHibernate IPreUpdateEventListener & IPreInsertEventListener
...Here comes the subtlety, however. We cannot just update the entity state. The reason for that is quite simple, the entity state was extracted from the entity and place in the entity state, any change that we make to the entity state would not be reflected in the entity itself. That may cause the database row and the entity instance to go out of sync, and make cause a whole bunch of really nasty problems that you wouldn’t know where to begin debugging.
You have to update both the entity and the entity state in these two event listeners (this is not necessarily the case in other listeners, by the way). Here is a simple example of using these event listeners...

I couldn't find some way to use the reflection to achieve what I described in my question above. I tried to use reflection because I didn't know about the Generators available in NHibernate (as I am new to NHibernate).
I have a table named sys_params which holds the next key values for different tables. My target was to fetch the next key for my table my_entity, assign it to the primary key of the new record, increment the next key value in the sys_params table and save the new record into the database.
To achieve this first I defined following classes.
public class NextIdGenerator : TableGenerator
{
}
public class NextIdGeneratorDef : IGeneratorDef
{
public string Class
{
get { return typeof(NextIdGenerator).AssemblyQualifiedName; }
}
public object Params
{
get { return null; }
}
public Type DefaultReturnType
{
get { return typeof(int); }
}
public bool SupportedAsCollectionElementId
{
get { return true; }
}
}
And then in my mapping class I defined the generator like below:
public class MyEnityMap : ClassMapping<MyEnity>
{
public MyEnityMap()
{
Table("my_entity");
Id(p => p.myId,
m=>{
m.Column("my_id");
m.Generator(new NextIdGeneratorDef(), g =>g.Params( new
{
table = "sys_params",
column = "param_nextvalue",
where = "table_name = 'my_entity'"
}));
});
.......
}
}
Hope this will help someone else. Improvements to this solution are highly appreciated.

Entity framework attach: object with same key exists

I am building a windows form application, and I use multiple DBContext instances (mostly one per Business layer call).
After literally days of dealing with an issue (while inserting new entities, the ones they referred to were added as new ones, instead of using the existing entities), I found out that the problem was I had to attach the existing entities to the context.
All was good for about 2 hours, when I then got errors while attaching: the entity with the same key exists in the context.
I tried testing before attaching (similar method for every entity type):
private void attachIfNeeded(POCO.Program myObject, myContext context)
{
if (!context.Set<POCO.Program>().Local.Any(e => e.ID == myObject.ID))
{
context.programs.Attach(myObject);
return true;
}
else
{
myObject = context.Set<POCO.Program>().Local.Single(e => e.ID == myObject.ID);
return false;
}
}
But the tests return false, but it still fails when attaching.
So basically, if I don't attach, it will add a new entity instead of using the existing (and intended) one. If I do attach, there's an error I can't figure out.
I have looked around (doing this the whole day now) and I actually (think I) know what the problem is:
The entity I am trying to add has multiple relationships, and other entities can be reached by multiple paths. Could that cause the problem?
Please help with this, solutions out there really make no sense to me and haven't worked.
I am really close to the point where I will try-catch around the attach statement and be done with it. But I will hate doing it.
Here are my entities (not all of them, but this should be enough):
public class Word
{
[Key]
public int ID {get;set;}
[Required]
public string word { get; set; }
public WordCategories category { get; set; }
public Word parent {get;set;}
public List<Unit> units { get; set; }
public Program program { get; set; }
public List<Lesson> lessons { get; set; }
public Word()
{
units = new List<Unit>();
lessons = new List<Lesson>();
}
}
public class Unit
{
[Key ]
public int ID { get; set; }
[Required]
public string name { get; set; }
public string description { get; set; }
public List<Lesson> lessons { get; set; }
public Program program {get;set;}
public List<Word> words { get; set; }
public Unit()
{
lessons=new List<Lesson>();
words = new List<Word>();
}
}
And here is where I am calling the attach method. The error is thrown on the first attach:
public int addWords(List<POCO.Word > words,int programID, int unitID,int lessonID)
{
CourseHelperDBContext context = getcontext();
int result;
foreach(POCO.Word a in words)
{
foreach (POCO.Unit b in a.units)
attachIfNeeded(b, context);
foreach(POCO.Lesson c in a.lessons )
attachIfNeeded(c,context);
attachIfNeeded(a.program,context);
if (a.parent != null)
attachIfNeeded(a.parent,context);
}
context.words.AddRange(words);
result = context.SaveChanges();
return result;
}
I cannot believe I'm having so many issues with this. I just want to store those entities, add some (I haven't gotten to the point where I would change them) and save it.
So far I've figured:
Some words are new, some exist and some are changed (mostly parent property);
All units exist, as do programs and lessons (so I need to attach them);
The object graph contains multiple paths to entities, some of which exist, some of which are new;
I am using a new context for every request. I run into other issues when I was using the same all the time. I found solutions that pointed to this pattern, and I think it's OK since that's what you'd do on an ASP MVC project.
All these could be causing problems, but I don't know which and how to work around them.
I think I can make this work by adding one word at a time, and pulling programs, lessons and units every time... but that means many many round trips to the DB. This can't be the way.

Back to this after quite some time, the problem in this case was that I needed to retrieve the entities that were present on my relationships.
The solution was neither attach (because it would fail if the entity is already attached) nor add (because it already existed on the DB).
What I should have done was to retrieve every entity related to the one I was adding.
This helped:
Entity Framework creating new entity with relationship to existing entity, results in attempt to create new copy of the existing entity

After attaching the entity, try setting the entity state to modified.
context.programs.Attach(myObject);
context.Entry(myObject).State = EntityState.Modified;
I think there's a mistake in your test logic.
If entity does not exist in database, you should be adding instead of attaching. Your code is attaching if it can't find an entity when it should really be adding.
Code to add a new entity (Create/Insert)
context.Set<T>.Add(entity);
Code to attach an entity (Update)
context.Set<T>.Attach(entity);
context.Entry(entity).State = EntityState.Modified;
If your code is failing on the first attach, that would be attachIfNeeded(b,context); ? I don't think you have shown us the code for this.

I share my experience with the same exception.
First, here is my code:
public void UpdateBulk(IEnumerable<Position> pDokumentPosition, DbDal pCtx)
{
foreach (Position vPos in pDokumentPosition)
{
vPos.LastDateChanged = DateTime.Now;
pCtx.Entry(vPos).State = EntityState.Modified;
}
pCtx.SaveChanges();
}
I got the same exception on the EntityState.Modified line.
In my case the problem was that, when set the vPos state to modified, then all the related objects (vPos.Document and vPos.Produkt) loaded in the context with unchanged state.
In the foreach first step it not makes any exception, just on the second step, because eg. the related Dokument entity has already been loaded in the memory/context (so the key property of the Dokument too).
And how i solve it? (maybe not the best solution):
I detach the related entites in every step with this lines:
if (vPos.Dokument != null)
{
pCtx.Entry(vPos.Dokument).State = EntityState.Detached;
}
if (vPos.Produkt!=null)
{
pCtx.Entry(vPos.Produkt).State = EntityState.Detached;
}
If you have better solution, I'm looking forward to it...

You can try this
context.words.Add(words);
result=context.SaveChanges();

"References" property not visible on the client's side

So as usual I have an issue with ria service + nhibernate. The question is how to make an entity property
, mapped using “references”, visible on the client side. The problem is that when you load an entity
without this field and try to save it , then missing values are updated as NULL inside db. Here’s class schema:
public class A
{
public virtual ComplexProperty property {get;set;}
}
public class AMap
{
public AMAP()
{
References(p=>p.property).Nullable().Column(“COMPLEX_PROPERTY_ID”);
}
}
(I've skipped parts with mapping/declaring key property as it's made inside underlying classes)
Usual trick with include and association attribute(like with HasMany) does not work as there is no real foreign_key property inside
class A

found a solution that's working for me. It's enough to add "fake" foreign key property to class A which is not mapped to database. It allows to define association:
public class A
{
[Include]
[Association("Relation1","ComplexPropertyId","Id")]
public virtual ComplexProperty property {get;set;}
public virtual int ? ComplexPropertyId {get;set;}
}
Last thing to do is to set ComplexPropertyId manually on the client side after retrieving objects from db(mappings remain as they were).
public IQueryable<A> GetA()
{
var item = repository.Query<A>();
foreach(var a in item) a.ComplexPropertyId = a.ComplexProperty.Id;
return item;
}