Enum resets to default value on insert. It can't differentiate between null and 0.

[gabrielheming]

I encountered this issue while working on my project.
It is a bit specific, and as far as I could investigate, it is related to directly to npgsql/efcore.pg than to dotnet/efcore itself.

The summarized scenario is the following:
When inserting an entity that has an enum as a property, this property has a default value that is different than the enum member that has 0 as value, it is not possible to insert the entity setting the property to the enum member that corresponds to 0.

I have encountered only one entry about this issue on stackoverflow. Also, I have look it up here on the issues, and I haven't found anything related.

I've made a repo to test/reproduce this behaviour. It test against PostgreSQL and InMemory database.
https://github.com/gabrielheming/enum-default-value-error

I hadn't time to test on different databases to be sure that it is specific here, but I think it can give you everything that is necessary.

To exemplify:

Entity

public class MyEntity
{
    public int MyEntityId { get; set; }
    public MyEnum MyEnum { get; set; }
}

Enum

public enum MyEnum
{
    First, // implicit value = 0
    Second // implicit value = 1
}

DbContext

public class AppDbContext : DbContext
{
    public DbSet<MyEntity> MyEntities { get; set; }

    public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
    {
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<MyEntity>()
            .Property(_ => _.MyEnum)
            .HasDefaultValue(MyEnum.Second)
            .HasConversion<string>();
    }
}

Ps.: I don't think converting to string adds any difference to the output, but I replicate as I had been using on my project.

Execution

var entity = new MyEntity()
{
     MyEnum = MyEnum.First
 };

context.MyEntities.Add(entity);
context.SaveChanges();

Expected result:
entity.MyEnum // First

Actual result:
entity.MyEnum // Second

Workaround to solve this problem

Change the MyEnum order to make sure that the default value is 0:

public enum MyEnum
{
    Second, // implicit value = 0
    First // implicit value = 1
}

Set the first item of the Enum as value 1:

public enum MyEnum
{
    First = 1,
    Second // implicit value = 2
}

[roji]

Duplicate of dotnet/efcore#15070

[roji]

See also dotnet/efcore#15070 which is specifically about warning for enums; that issue contains lots of explanations about what's going on and possible workarounds.

[gabrielheming]

May I ask you where I can find about #15070, there is no link about it. Also, I couldn't find the relation between this issue and the #701. I'm not saying that this isn't a duplication, it is just seems unrelated.

[roji]

Sorry, I messed up the links above - they should have been to the EF Core repo. I've corrected them.