Entity Framework Core is trying to insert duplicated records when SaveChanges() is called

Question

My Entities are:

public class Customer
{
   ...
   public virtual ICollection<ShoppingCartItem> ShoppingCartItems { get; set; }
   ...
}

public class ShoppingCartItem
{
   public string CustomerId { get; set; }
   public int ProductId { get; set; }
   public virtual Customer { get; set; }
   public virtual Product{ get; set; }
   ...
}

The add method is:

public async Task AddAsync(TEntity entity)
{
    await Task.Factory.StartNew(() => this.entities.Add(entity));
}

The entity that I am adding is:

ShoppingCartItem()
{
    CustomerId = "xxxxx",
    ProductId = 1,
    Customer = null,
    Product = null 
}

When I call SaveChanges() the EF is trying to insert two identical records for ShoppingCartItem. The ShoppingCartItem is created and added to the context only once. Any ideas what possibly could be wrong?

EDIT:

This is how I call the AddSync method:

public async Task AddNewCartItem(ShoppingCartItem shopingCartItem)
    {
        await this.ShoppingCartItemRepository.AddAsync(shopingCartItem);
        await this.SmartStoreWorkData.CompleteAsync();
    }

EF can only do updates if you have a unique primary key. Otherwise it has no way of knowing what is a duplicate or not. — Sam Axe
– Sam Axe, Commented Dec 17, 2016 at 14:01
Why is the add method async? There's no point in that at all. — DavidG
– DavidG, Commented Dec 17, 2016 at 14:07
@SamAxe the the ShoppingCartItem has primary key. @DavidG either ways the EF is trying to add two records. — Kos
– Kos, Commented Dec 17, 2016 at 14:13

sellotape · Accepted Answer · 2016-12-17 16:24:00Z

3

DbContext is not thread safe. By - pointlessly, as noted in the comments - performing your .Add() in what is quite likely a different thread, you're confusing the DbContext. Add() is purely an in-memory operation; there is no reason to try to make it async. Change that and I reckon it will resolve the issue.

public void Add(TEntity entity)
{
    this.entities.Add(entity);
}

If you have any other similar usages that are not shown in your question, change those to sync too.

You can do "proper" async with DbContext but it is only for the methods that actually talk to the database, not the in-memory ones, and will not usually involve Task.<anything>, just the provided async methods.

Edit: for completeness, the link above is for EF6, but in EF Core, DbContext is also not thread-safe.

edited Dec 17, 2016 at 16:24

answered Dec 17, 2016 at 15:46

sellotape

8,4252 gold badges29 silver badges33 bronze badges

Sign up to request clarification or add additional context in comments.

10 Comments

Kos Over a year ago

Thank you for the clarification when async have to be used. But this does not solve the problem as I mentioned in the comments . I changed the Add method and the EF still tries to add second time the same record in the same SaveChanges() call.

sellotape Over a year ago

@Kos - you're not perhaps adding the item to the ShoppingCartItems collection and via this.entities.Add(entity) are you? If not, would you show us the code for CompleteAsync() please (by editing the original question). Also show us where your DbContext is created. In general we can help you better if you show quite a bit more code that might be relevant.

Kos Over a year ago

I do not add the ShoppingCartItem to the Customer.ShoppingCartItems collection. The CompleteAsync() method looks like await this.dbContext.SaveChangesAsync();. I am injecting the DbContext in here services.AddTransient<ISmartStoreWorkData, SmartStoreWorkData>(); which is my UnitOfWork. Seems like that double records insert happens with tables that have many-to-many relationship.

Kos Over a year ago

repository link

sellotape Over a year ago

You imply the primary key for ShoppingCartItem is the DB-generated ID, but in the fluent config (in your linked code) you actually set it to { CustomerId, ProductId }: builder.Entity<ShoppingCartItem>().HasKey(x => new { x.CustomerId, x.ProductId });. Can you confirm there is no other row in the table with that primary key?

|

Andrés Robinet · Accepted Answer · 2016-12-19 03:02:30Z

2

UPDATE: I did the following:

Cloned your repo link: SmartStoreNETCore
Migrated to .NET Core 1.1 with the new EF tooling (preview4)
Added the configuration as specified in EF ModelBuilder below
Applied Migration and updated database

Commands:

dotnet ef --startup-project ../SmartStoreNetCore.Web/ migrations add ChangeShoppingCartItemKey
dotnet ef --startup-project ../SmartStoreNetCore.Web/ database update

Removed the following duplicate tag in _Layout.cshtml

<script src="~/js/site.js" asp-append-version="true"></script>

site.js contains the click event handler for the Add To Cart functionality

Started the site and everything worked as expected, no duplicate shopping cart items and the quantity is updated as expected

In summary

I can fully confirm the following method was being called twice before removing the duplicate reference to site.js:

 public async Task AddNewCartItem(ShoppingCartItem shopingCartItem)
 {
     await this.ShoppingCartItemRepository.AddAsync(shopingCartItem);
     await this.SmartStoreWorkData.CompleteAsync();
 }

It is a mistery to me why you didn't catch this before via debugging

EF ModelBuilder

Your configuration should look like:

builder.Entity<ShoppingCartItem>().HasKey(x => x.Id); // Notice this!
builder.Entity<ShoppingCartItem>().Property(x => x.Id).ValueGeneratedOnAdd(); // Also this!
builder.Entity<ShoppingCartItem>().HasOne(s => s.Customer).WithMany(b => b.ShoppingCartItems).OnDelete(DeleteBehavior.Restrict);
builder.Entity<ShoppingCartItem>().HasOne(s => s.Product).WithMany().OnDelete(DeleteBehavior.Restrict);

Having a value generated automatically does not define it as the primary key

edited Dec 19, 2016 at 3:02

answered Dec 17, 2016 at 18:14

Andrés Robinet

1,53712 silver badges19 bronze badges

7 Comments

Kos Over a year ago

In this case I am getting the second duplicated record inserted into the database.

Andrés Robinet Over a year ago

Which DB engine are you using?

Kos Over a year ago

SQL Server Database. Just to clear that... duplicated record but with different Id.

Andrés Robinet Over a year ago

Mmm... can only think of a bug at this point. I don't know... Are you using the latest EF Core? Check this answer I gave the other day

Andrés Robinet Over a year ago

The latest version is 1.1.0, but I'm not sure if this what you are experiencing is a bug in previous EF Core versions, in the current version of EF or in your code :(, so I can't even tell you an upgrade will fix it

|

Collectives™ on Stack Overflow

Entity Framework Core is trying to insert duplicated records when SaveChanges() is called

2 Answers 2

10 Comments

In summary

EF ModelBuilder

7 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

10 Comments

In summary

EF ModelBuilder

7 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related