如何使用实体框架正确建模自引用多父项关系

Z时代
2024-01-10
分类：问答

我试图在EF6中为以下自引用人类建模。如何使用实体框架正确建模自引用多父项关系

public class Person 
{ 
    public int ID { get; set; } 
    public string Name { get; set; } 
    public int? MotherId { get; set; } 
    public Person Mother { get; set; } 
    public int? FatherId { get; set; } 
    public Person Father { get; set; } 
    public virtual ICollection<Person> Children { get; set; } 
}

而且我的DbContext是这样的：

public virtual DbSet<Person> People { get; set; } 
protected override void OnModelCreating(DbModelBuilder modelBuilder) 
{ 
    modelBuilder.Entity<Person>() 
     .HasOptional(m => m.Mother) 
     .WithMany(c => c.Children) 
     .HasForeignKey(m => m.MotherId); 
    modelBuilder.Entity<Person>() 
     .HasOptional(f => f.Father) 
     .WithMany(c => c.Children) 
     .HasForeignKey(f => f.FatherId); 
}

当尝试使用下面的代码的人添加到数据库：

db.People.Add(new Person { Name = "Jane Doe" });

我得到这个错误：

An unhandled exception of type 'System.InvalidOperationException' occurred in EntityFramework.dll
Additional information: Sequence contains no matching element

这个错误是什么意思，我该如何纠正？另外，有没有更好的方法来建模这个对象（例如：使用母亲的子类：人和父：人）？

回答：

我想出了以下的解决方案，产生一个干净的数据库，并允许更大的灵活性，将关系时：

public interface IParent 
{ 
    ICollection<Person> Children { get; set; } 
} 
public class Person 
{ 
    public int ID { get; set; } 
    public string Name { get; set; } 
    public int? MotherId { get; set; } 
    public Female Mother { get; set; } 
    public int? FatherId { get; set; } 
    public Male Father { get; set; } 
} 
public class Male : Person, IParent 
{ 
    public virtual ICollection<Person> Children { get; set; } 
} 
public class Female : Person, IParent 
{ 
    public virtual ICollection<Person> Children { get; set; } 
}

的的DbContext只包含：

public virtual DbSet<Person> People { get; set; } 
public virtual DbSet<Female> Females { get; set; } 
public virtual DbSet<Male> Males { get; set; }

而生成的数据库是这样的：

ID Name MotherId FatherId Discriminator 1 Jane NULL NULL Female 2 John NULL NULL Male 3 Jimmy 1 2 Male 4 Jenn 1 2 Female

该解决方案还提供了将在多个方面关系的灵活性：

mom.Children.Add(son); // or 
son.Mother = mom;

回答：

我会做以下事情。虽然它可能不适合你“在实体框架的要求

public class Person 
{ 
    public int ID { get; set; } 
    public string Name { get; set; } 
    public int? MotherId { get; set; } 
    public int? FatherId { get; set; } 
} 
public Class RelationFinder 
{ 
    Public Person GetMother(IEnumerable<Person> people, Person child) 
    { 
     return people.FirstOrDefault(p=>p.Id = child.MotherId); 
    } 
    Public Person GetFather(... 
    Public IEnumerable GetChildern(... 
}