How do we manage the order of updates when using a filtered unique index?

[sebdesalvador]

The question

I have a filtered unique index defined as:

builder
    .HasIndex(e => new { e.UserId, e.IsDefault })
    .HasFilter($"[{nameof(MyEntity.IsDefault)}] = 1")
    .IsUnique()
    .HasDatabaseName($"UX_{nameof(MyEntity)}_{nameof(MyEntity.UserId)}_{nameof(MyEntity.IsDefault)}");

It translates into:

CREATE UNIQUE NONCLUSTERED INDEX [UX_MyEntity_UserId_IsDefault] ON [dbo].[MyEntity]
(
    [UserId] ASC,
    [IsDefault] ASC
)
WHERE ([IsDefault]=(1))

Because I can only have 1 record with the flag IsDefault set to true, the order of updates is important, I first need to set non default records to false, and then set the default one. Since the EF Core doesn't really know the condition/filter, it doesn't order the updates correclty and I often get an error with the message:

Cannot insert duplicate key row in object 'dbo.MyEntity' with unique index 'UX_MyEntity_UserId_IsDefault'.

Example

In the database I have:

Id	UserId	IsDefault
1	5	0
2	5	1
3	5	0

In the code we have a Parent and a Child object, the Parent has a collection of Children and it goes like this:

var parent = await parentEfRepository.GetByIdAsync(5, cancellationToken);
var newDefaultChild = parent.Children.Where(c => ...);
newDefaultChild.SetAsDefault();
await context.SaveChangesAsync(cancellationToken);

The SetAsDefault() method contains the logic to set other Children as non default and the result is that only 1 Child is marked as being the default one.
When we get to SaveChanges(), EF generates a SQL script that contains the updates which look like this:

SET NOCOUNT ON;
UPDATE [MyEntity] SET [IsDefault] = @p0
OUTPUT INSERTED.[PeriodEnd], INSERTED.[PeriodStart]
WHERE [Id] = @p1;
UPDATE [MyEntity] SET [IsDefault] = @p2
OUTPUT INSERTED.[PeriodEnd], INSERTED.[PeriodStart]
WHERE [Id] = @p3;

Because it's trying to update record with ID 1 first, we would end up with the following:

Id	UserId	IsDefault
1	5	1
2	5	1
3	5	0

And that's when the unique constraint kicks in and throws an error.
I have started experimenting with interceptors but it's getting dirty, surely someone had this issue before me?

Thanks!

Provider and version information

EF Core version: 8.0.11
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET 8.0
Operating system: Windows
IDE: Rider