Question

我有两张桌子 -

 1. Account 

 2. Users

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

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，但根据我的原始计划，它们在数据库中被定义为非空。谁能知道如何将外键定义为可空？

Answer 1

如果您想拥有 nullable 外键，为什么要将其定义为 required ：

this.HasRequired

改为使用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key-property，这首先是代码的想法：）

根据this article by Microsoft，删除外键属性应该足够了。看看文章中图1和图2之间的差异。（密钥当然会在数据库级别生成，但你真的需要在模型中使用它们吗？）

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

2 个答案: