EF Code First 5 - 如何使用 Fluent API 定义可为空的外键？

Question

我有两张桌子-

 1. Account 

 2. Users

在Account表中，DefaultExpensePartner和AccountOwner是Users表的UserId字段的外键。我已经定义了如下类。

public class Account
{
    public int AccountId { get; set; }
    public string AccountName { get; set; }
    public int? AccountOwnerId { get; set; }
    public int? DefaultExpensePartnerId { get; set; }

    public virtual Users AccountOwner { get; set; }
    public virtual Users DefaultExpensePartner { get; set; }
}

public class AccountConfiguration : EntityTypeConfiguration<Account>
{
    public AccountConfiguration()
    {
        this.ToTable("Account");

        this.HasKey(c => c.AccountId);

        this.Property(c => c.AccountId)
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity)
            .IsRequired();

        this.Property(c => c.AccountName)
            .HasMaxLength(50)
            .IsRequired();

        this.Property(c => c.AccountOwnerId)
            .HasColumnName("AccountOwner")
            .IsOptional();

        this.Property(c => c.DefaultExpensePartnerId)
            .HasColumnName("DefaultExpensePartner")
            .IsOptional();

        this.HasRequired(c => c.DefaultExpensePartner)
            .WithMany()
            .HasForeignKey(c => c.DefaultExpensePartnerId)
            .WillCascadeOnDelete(false);

        this.HasRequired(c => c.AccountOwner)
           .WithMany()
           .HasForeignKey(c => c.AccountOwnerId)
           .WillCascadeOnDelete(false);
    }
}

public class Users
{
    public int UserId { get; set; }
    public string Email { get; set; }
    public string DisplayName { get; set; }
    public string PasswordSalt1 { get; set; }
    public string PasswordSalt2 { get; set; }
    public string PasswordHash { get; set; }
}

public class UsersConfiguration : EntityTypeConfiguration<Users>
{
    public UsersConfiguration()
    {
        this.ToTable("Users");

        this.HasKey(c => c.UserId);

        this.Property(c => c.UserId)
            .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity)
            .IsRequired();

        this.Property(c => c.Email)
            .HasMaxLength(80)
            .IsRequired();

        this.Property(c => c.DisplayName)
            .HasMaxLength(50)
            .IsRequired();

        this.Property(c => c.PasswordSalt1)
            .HasMaxLength(172)
            .IsRequired();

        this.Property(c => c.PasswordSalt2)
            .HasMaxLength(172)
            .IsRequired();

        this.Property(c => c.PasswordHash)
            .HasMaxLength(40)
            .IsRequired();
    }
}

虽然我能够为AccountOwner 和DefaultExpensePartner 字段建立外键关系，但它们在数据库中被定义为非空，这根据我的原计划是不正确的。谁能知道如何将外键定义为可为空的？

Answer 1

如果你想拥有 nullable 外键，为什么要将它定义为必需：

this.HasRequired

?

改用HasOptional：

        this.HasOptional(c => c.AccountOwner)
            .WithMany()
            .HasForeignKey(c => c.AccountOwnerId)
            .WillCascadeOnDelete(false);

Answer 2

除非你真的想要，否则你不必指定键属性，这有点代码优先的想法:)

根据this article by Microsoft 应该足以删除外键属性。看看文章中图1和图2的区别。 （密钥当然会在数据库级别生成，但模型中真的需要它们吗？）