EF Core TPT为何同时生成基类与派生类的外键？

我有一个模型，其中Company和NaturalPerson均继承自Person（公司属于法人）。公司和自然人都可以拥有资产，因此我创建了Ownership对象来关联Person，该Person可以是Company或NaturalPerson。

使用TPT生成模型时，已生成Person、Company、NaturalPerson表，这部分正常。但Ownership表中，我预期仅存在指向Person表的1个外键，却额外生成了指向Company和NaturalPerson表的2个外键，总计3个。请问这是否正常？若正常，原因是什么？还是我配置出错了？

代码示例 #

public class MyContext : DbContext
{
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<Person>().ToTable("Person");
        modelBuilder.Entity<NaturalPerson>().ToTable("NaturalPerson");
        modelBuilder.Entity<LegalPerson>().ToTable("LegalPerson");
        modelBuilder.Entity<CompanyThatCannotOwnStuff>().ToTable("CompanyThatCannotOwnStuff");
        modelBuilder.Entity<Company>().ToTable("Company");
        modelBuilder.Entity<SharableGood>().ToTable("Good");
        modelBuilder.Entity<Ownership>()
            .HasOne(o => o.Owner)
            .WithMany()
            .HasForeignKey(o => o.OwnerId)
            .OnDelete(DeleteBehavior.NoAction);
        modelBuilder.Entity<Ownership>()
            .HasOne(o => o.SharableGood)
            .WithMany()
            .HasForeignKey(o => o.SharableGoodId)
            .OnDelete(DeleteBehavior.NoAction);
    }
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        base.OnConfiguring(optionsBuilder);
        optionsBuilder.UseSqlServer("Server=localhost;Database=Test;Trusted_Connection=True;");
    }
}

public abstract class Person
{
    public Guid Id { get; set; }
}

public class NaturalPerson : Person
{
    public List<Ownership> Ownerships { get; set; }
}

public class LegalPerson : Person { }

public class CompanyThatCannotOwnStuff : LegalPerson { }

public class Company: LegalPerson
{
    public List<Ownership> Ownerships { get; set; }
}

public class SharableGood
{
    public Guid Id { get; set; }
}

public class Ownership
{
    public Guid Id { get; set; }
    public Guid SharableGoodId { get; set; }
    public SharableGood SharableGood { get; set; }
    public Guid OwnerId { get; set; }
    public Person Owner { get; set; }
    public DateTime ImportantDate { get; set; }
}

生成的Ownership表迁移代码 #

migrationBuilder.CreateTable(
    name: "Ownership",
    columns: table => new
    {
        Id = table.Column<Guid>(type: "uniqueidentifier", nullable: false),
        SharableGoodId = table.Column<Guid>(type: "uniqueidentifier", nullable: false),
        OwnerId = table.Column<Guid>(type: "uniqueidentifier", nullable: false),
        ImportantDate = table.Column<DateTime>(type: "datetime2", nullable: false),
        CompanyId = table.Column<Guid>(type: "uniqueidentifier", nullable: true),
        NaturalPersonId = table.Column<Guid>(type: "uniqueidentifier", nullable: true)
    },
    constraints: table =>
    {
        table.PrimaryKey("PK_Ownership", x => x.Id);
        table.ForeignKey(
            name: "FK_Ownership_Company_CompanyId",
            column: x => x.CompanyId,
            principalTable: "Company",
            principalColumn: "Id");
        table.ForeignKey(
            name: "FK_Ownership_Good_SharableGoodId",
            column: x => x.SharableGoodId,
            principalTable: "Good",
            principalColumn: "Id");
        table.ForeignKey(
            name: "FK_Ownership_NaturalPerson_NaturalPersonId",
            column: x => x.NaturalPersonId,
            principalTable: "NaturalPerson",
            principalColumn: "Id");
        table.ForeignKey(
            name: "FK_Ownership_Person_OwnerId",
            column: x => x.OwnerId,
            principalTable: "Person",
            principalColumn: "Id");
    });

解答 #

这是配置错误导致的，核心原因是派生类的导航属性未与Ownership.Owner正确关联，EF Core误生成了额外的独立关联。

问题根源 #

你的NaturalPerson和Company类中都定义了List<Ownership>导航属性，但在OnModelCreating中，你仅配置了Ownership.Owner到Person的关联（且WithMany()未指定对应导航属性），EF Core会默认将派生类中的Ownerships视为全新的、独立的关联关系，因此为每个派生类生成了单独的外键列（CompanyId、NaturalPersonId），再加上你手动配置的OwnerId，最终出现三个外键。

修复方案 #

修改OnModelCreating，明确派生类的Ownerships导航属性与Ownership.Owner的关联：

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);

    modelBuilder.Entity<Person>().ToTable("Person");
    modelBuilder.Entity<NaturalPerson>().ToTable("NaturalPerson");
    modelBuilder.Entity<LegalPerson>().ToTable("LegalPerson");
    modelBuilder.Entity<CompanyThatCannotOwnStuff>().ToTable("CompanyThatCannotOwnStuff");
    modelBuilder.Entity<Company>().ToTable("Company");
    modelBuilder.Entity<SharableGood>().ToTable("Good");

    // 配置NaturalPerson与Ownership的关联
    modelBuilder.Entity<NaturalPerson>()
        .HasMany(n => n.Ownerships)
        .WithOne(o => o.Owner)
        .HasForeignKey(o => o.OwnerId)
        .OnDelete(DeleteBehavior.NoAction);

    // 配置Company与Ownership的关联
    modelBuilder.Entity<Company>()
        .HasMany(c => c.Ownerships)
        .WithOne(o => o.Owner)
        .HasForeignKey(o => o.OwnerId)
        .OnDelete(DeleteBehavior.NoAction);

    // 保留SharableGood的关联配置
    modelBuilder.Entity<Ownership>()
        .HasOne(o => o.SharableGood)
        .WithMany()
        .HasForeignKey(o => o.SharableGoodId)
        .OnDelete(DeleteBehavior.NoAction);
}

这样配置后，EF Core会将所有派生类的Ownerships导航属性映射到同一个OwnerId外键，不会再生成多余的CompanyId和NaturalPersonId列。

内容的提问来源于stack exchange，提问作者Seb