I have one property in an entity that is the type of Guid it’s unique but nullable.

Since null GUID is equal to 00000000-0000-0000-0000-000000000000, the PostgreSQL disallows me from inserting a second record where the Guid is null (all zeroes) as it violates the index constraint.

Because of this I’ve tried to configure NULLS NOT DISTINCT by adding AreNullsDistinct(false) to the index.

public class Employee
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public required Guid Id { get; set; }
    public required string FirstName { get; set; }
    public required string LastName { get; set; }
    public Guid? AdObjectId { get; set; } // Link employee back to identity in AD, can be null as some employee might not present in the AD
}

public class DatabaseContext : DbContext
{
    public DbSet<Employee> Employee { get; set; }

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

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Employee>().HasIndex(e => e.AdObjectId).IsUnique().AreNullsDistinct(false);
    }
}

However, when I inspect the DDL, the NULLS NOT DISTINCT are absent from the index:

create table "Employee"
(
    "Id"         uuid                           not null
        constraint "PK_Employee" primary key,
    "FirstName"  text                           not null,
    "LastName"   text                           not null,
    "AdObjectId" uuid                           not null,
);

create unique index "IX_Employee_AdObjectId"
    on "Employee" ("AdObjectId");

Below is the migration (only the index creation part) for reference:

migrationBuilder.CreateIndex(
    name: "IX_Employee_AdObjectId",
    table: "Employee",
    column: "AdObjectId",
    unique: true)
    .Annotation("Npgsql:NullsDistinct", false);

I am wondering, do I miss any additional configuration for the NULLS NOT DISTINCT to be present on the index?

Environment details:

• .NET Core 8
• PostgreSQL 16
• Microsoft.EntityFrameworkCore: 8.0.4
• Microsoft.EntityFrameworkCore.Design: 8.0.4
• Npgsql.EntityFrameworkCore.PostgreSQL: 8.0.4