public class TestContext : DbContext
{
  DbSet<ImplementClassOne> Ones { get; set; }
  DbSet<ImplementClassTwo> Twos { get; set; }

  protected void OnModelCreating(ModelBuilder builder)
  {
    modelBuilder.Entity<Base>().HasDiscriminator<string>("Type")
      .HasValue<ImplementClassOne>("one")
      .HasValue<ImplementClassTwo>("two");

    modelBuilder.Entity<Base>().Property(base => base.UniqueVal)
      .IsRequired();

    modelBuilder.Entity<Base>().Property(base => base.RequiredVal)
      .IsRequired();

    modelBuilder.Entity<ImplementClassOne>().HasIndex(one => one.UniqueVal)
      .IsUnique()
      .HasFilter("Type = 'one'");

    modelBuilder.Entity<ImplementClassTwo>().HasIndex(two => two.UniqueVal)
      .IsUnique()
      .HasFilter("Type = 'two'");
  }
}

protected override void Up(MigrationBuilder migrationBuilder)
{
  migrationBuilder.CreateTable(
    name: "Base",
    columns: table => new
    {
      Id = table.Column<int>(type: "int", nullable: false)
        .Annotation(...),
      UniqueVal = table.Column<string>(type: "nvarchar(max)", nullable: false,
      RequiredVal = table.Column<string>(type: "nvarchar(max)", nullable: false
    },
    constraints: table =>
    {
      table.PrimaryKey("PK_Base", x => x.Id);
    });

  migrationBuilder.CreateIndex(
    name: "IX_Base_UniqueVal_One",
    table: "Base",
    column: "UniqueVal",
    unique: true,
    filter: "Type = 'one'");
}