dbContext.<Entity>.Update() is creating new records

[DiegoZoracKy]

When i do something like:

var e = new Entity();
e.Id = 100;
e.Name = "Name 100";
dbContext.Entities.Update(e);
dbContext.SaveChanges();

a new record is created.

Is this the correct behaviour?

[rowanmiller]

@DiegoZoracKy it should attempt to update an existing record, not insert a new one. Can you share a full code listing that we can use to reproduce the issue? (i.e. the code for Entity and your context)

[DiegoZoracKy]

@rowanmiller i've created something simple to show the case. See:

using Microsoft.AspNet.Mvc;
using System.Linq;
using Microsoft.Data.Entity;
using Newtonsoft.Json.Linq;

public class TestUpdate
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class MyContext : DbContext
{
    public DbSet<TestUpdate> TestUpdates { get; set; }      
}           

[Route("api/[controller]")]
public class TestController : Controller
{
    private MyContext dbContext;

    public TestController(MyContext context)
    {
        dbContext = context;
    }

    [HttpGet]
    public IActionResult Get()
    {
        var e = new TestUpdate();
        e.Name = "Name 100";
        dbContext.TestUpdates.Update(e);
        dbContext.SaveChanges();

        return new ObjectResult(dbContext.TestUpdates.AsNoTracking().ToList());
    }
}   

Every time you hit api/test (GET) a new record will be saved.

[DiegoZoracKy]

@rowanmiller i've found what it seems to be another weird behavior on Update method. Let's suppose that in my previous example, AnotherClass exists on the project and it makes a reference to TestUpdate, like:

    public class AnotherClass
    {
        public int Id { get; set; }
        public virtual List<TestUpdate> TestUpdate { get; set; }
    }

Thinking about SQLServer, this will create a column AnotherClassId on the TestUpdate Table, with a reference to records on AnotherClass, right?

The problem is that when i do .Update on TestUpdate, this reference is being set to NULL.

[rowanmiller]

@DiegoZoracKy regarding the first issue you reported...

This situation is arising because TestUpdate.Id is assigned a value of 0. The fact that we are implying this means it is added (even though you called Update) is a bug and we will fix it. That said, do you actually have an existing row in the database with an Id of zero... or is that just a coding error where you are not setting the key property?

If having a key value of zero is a legitimate requirement, then you can workaround this until we fix the bug by explicitly setting the state (rather than calling Update).

dbContext.Entry(e).State = EntityState.Modified;

[rowanmiller]

@DiegoZoracKy can you open a new issue for the second case you mentioned (and include code that demonstrates the issue again).

[DiegoZoracKy]

@rowanmiller No, id 0 is not a requirement of my software. I've created this simple example for you to see that the Update method is creating new records. Good that it is a Bug and not its correct behavior.

I will create a new issue for sure, within some hours. This current issue is something easy to be avoided, just bringing a performance penalty by checking if the record exists for real before update it. But this last one can be a huge problem.

[rowanmiller]

@DiegoZoracKy just to be clear, it only inserts a row if the key is set to zero. If it is set to anything else then it will correctly update it.

i.e. this code

var e = new TestUpdate();
e.Name = "Name 100";
e.Id = 5;
dbContext.TestUpdates.Update(e);
dbContext.SaveChanges();

Produces this SQL

exec sp_executesql N'SET NOCOUNT OFF;
UPDATE [TestUpdate] SET [Name] = @p1
WHERE [Id] = @p0;
SELECT @@ROWCOUNT;
',N'@p0 int,@p1 nvarchar(4000)',@p0=5,@p1=N'Name 100'

Not saying that it's not a bug... but just that you'll only see the insert behavior if you are attempting to update an entity with a key set to zero.

[DiegoZoracKy]

@rowanmiller i just tried setting a value to Id, like that:

var e = new TestUpdate();
e.Id = 100;
e.Name = "Name 100";
dbContext.TestUpdates.Update(e);
dbContext.SaveChanges();

And a new record was created. But for this test i used inMemory (EntityFramework.InMemory: 7.0.0-rc1-final) instead of SQL Server.

[DiegoZoracKy]

@rowanmiller And, a new issue about the reference being lost during Update, that i commented above: #3948

[rowanmiller]

@DiegoZoracKy I was able to reproduce that issue with InMemory. It's different from the original bug on this issue (which is already fixed), so I opened #3953 for the new issue.

[DiegoZoracKy]

Thanks @rowanmiller. I will track this new issue.

[rowanmiller]

Re-opening as we still need this to track the issue where the entity being passed to Update is marked as added if it has no key value assigned.