在C#中，是否可以用两个类引用外键？

Question

假设我有两个类 Country 和 Currency我想用EF在它们之间创建一个关系。

public class Country
{
    public long Id {get; set;}
    public string Name {get; set;} 

    public long? CurrencyId {get; set;}
    public Currency Currency {get; set;}
}

public class Currency
{
    public long Id {get; set;}
    public string Name {get; set;} 

    public long? CountryId {get; set;}
    public Country Country {get; set;}
}

我不能管理这个，我有一些模型在同一类型的。像 User 和 Organization.

安 Organization 有 Nullable UserId和 User 拥有 Nullable organization. 如何管理这个问题？

Answer 1

你完全可以有这样的关系，但它们必须正确配置，有时你必须插入实体，然后再更新它们，以绕过插入时而不是提交时的FK执行。

特别是当两个实体之间有多个关系时，EF没有约定来匹配反导航属性。

EG

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }

    public int DepartmentId { get; set; }

    [InverseProperty(nameof(EfCore3Test.Department.Members))]
    public Department Department { get; set; }

    [InverseProperty(nameof(EfCore3Test.Department.Manager))]
    public virtual ICollection<Department> ManagedDepartments { get; } = new HashSet<Department>();
}
public class Department
{
    public int Id { get; set; }
    public virtual ICollection<Person> Members { get; } = new HashSet<Person>();
    public Person Manager { get; set; }
    public int ManagerId { get; set; }
}

而你通常不能在所有的FK上都有级联行为，所以你至少要配置一个不级联。

modelBuilder.Entity<Department>()
            .HasMany(d => d.Members)
            .WithOne(m => m.Department)
            .OnDelete(DeleteBehavior.NoAction);

Answer 2

public class Country
{
    public long Id {get; set;}
    public string Name {get; set;} 

    public long? CurrencyId {get; set;}
    [ForeignKey("CurrencyId")]
    public virtual Currency Currency {get; set;}
}

public class Currency
{
    public long Id {get; set;}
    public string Name {get; set;} 

    public long? CountryId {get; set;}
    [ForeignKey("CountryId")]
    public virtual Country Country {get; set;}
}

你将需要参考 using System.ComponentModel.DataAnnotations.Schema;