EF Core 中必需到可选关系（一对零或一）的最佳方法是什么？

Question

我已经将EntityFramework 6的项目实现到EntityFramework Core中。我必须将 EF6 关系模式迁移到 EF 核心。 我在下面找到了一些参考资料：

1. Entity Framework Core zero-or-one to zero-or-one relation

但对 EF-Core 中的必需-可选关系没有任何想法。

Sample1.cs：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<StudentAddress>()
                .HasRequired(x => x.Student)
                .WithOptional(x => x.StudentAddress);
}

public class Student
{
    public int StudentId { get; set; }
    public string StudentName { get; set; }
    public virtual StudentAddress StudentAddress { get; set; }
}

public class StudentAddress
{
    public int StudentId { get; set; }
    public string State { get; set; }
    public virtual Student Student { get; set; }
}

Sample2.cs：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<StudentAddress>()
                .HasKey(sa => sa.StudentId);
    modelBuilder.Entity<StudentAddress>()
                .HasRequired(x => x.Student)
                .WithOptional(x => x.StudentAddress);
}

public class Student
{
    public int StudentId { get; set; }
    public string StudentName { get; set; }
    public virtual StudentAddress StudentAddress { get; set; }
}

public class StudentAddress
{
    public int StudentId { get; set; }
    public string State { get; set; }
    public virtual Student Student { get; set; }
}

请有人帮助我如何在 EF-Core 中使用流利的 api 做到这一点

Answer 1

你可以试试这个（参考：docs）：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<StudentAddress>()
                .HasOne(x => x.Student)
                .WithOne(x => x.StudentAddress).IsRequired(false);
}

或者，您可以在您的 Student 模型中添加一个 FK StudentAddressId 并让类型可以为空 int?

public class Student
{
    public int StudentId { get; set; }
    
    // This is the FK for StudentAddress.
    // Make it int? (nullable) if StudentAddress is optional
    public int? StudentAddressId { get; set; }
    public virtual StudentAddress StudentAddress { get; set; }
}

public class StudentAddress
{
    public int StudentId { get; set; }

    public virtual Student Student { get; set; }
}

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    // Since the FK is nullable, you don't need the IsRequired(false)
    modelBuilder.Entity<StudentAddress>()
                .HasOne(x => x.Student)
                .WithOne(x => x.StudentAddress);
}