EntityFrameworkCore无法生成表

Question

我在Asp.NetCore中实现了EntityFrameworkCore，但是下面的代码无法在SQL Express中生成表，它只生成身份表和文档，但没有Standard和Form。

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }
    public DbSet<Standard> Standard { get; set; }
    public DbSet<Form> Form { get; set; }
    public DbSet<MasterDocument> Document { get; set; }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);
        // Customize the ASP.NET Identity model and override the defaults if needed.
        // For example, you can rename the ASP.NET Identity table names and more.
        // Add your customizations after calling base.OnModelCreating(builder);
        //builder.Entity<Standard>().ToTable("Standard");
        //builder.Entity<Form>().ToTable("Form");
        //builder.Entity<MasterDocument>().ToTable("Document");

        builder.Entity<Form>()
            .HasOne(f => f.Standard)
            .WithMany(s => s.Forms)
            .HasForeignKey(k => k.StandardId)
            .OnDelete(DeleteBehavior.Restrict);

    }
}

模型

public class MasterDocument 
{
    public int ID { get; set; }
    [Required]
    [Display(Name = "EStandard")]
    [StringLength(50)]
    public string EStandard { get; set; }
    [Required]
    [Column("Betegnelse")]
    [Display(Name = "Betegnelse")]
    [StringLength(60)]
    public string Betegnelse { get; set; }
    [Display(Name = "Kommentar")]
    public string Comment { get; set; }
}
public class Standard : MasterDocument
{
    [Display(Name = "Dokumenter")]
    public ICollection<Form> Forms { get; set; }
}
public class Form : MasterDocument
{
    public String Status { get; set; }
    public int StandardId { get; set; }
    //[ForeignKey("StandardId")]
    public Standard Standard { get; set; }
}

任何帮助都将不胜感激。