自引用多对多关系 [英] Self Referencing Many-to-Many relations

问题描述

我有一个Ticket实体:

    public class Ticket
    { 
        public int Id { get; set; }
        public string Title { get; set; }

        public virtual ICollection<Relation> RelatedTickets { get; set; }
    }

我想在Entity Framework Core中设置多对多自相关，所以我建立了两个一对多关系:

I want to setup many-to-many self-relations in Entity Framework Core, so i made two one-to-many relations:

public class Relation
{
    [Required, ForeignKey("TicketFrom")]
    public int FromId { get; set; }

    [Required, ForeignKey("TicketTo")]
    public int ToId { get; set; }

    public virtual Ticket TicketFrom { get; set; }
    public virtual Ticket TicketTo { get; set; }
}

我尝试使用流利的API创建关系:

I've tried to create the relationship using fluent API:

        builder.Entity<Relation>()
               .HasKey(uc => new { uc.FromId, uc.ToId });
        builder.Entity<Relation>()
           .HasOne(c => c.TicketFrom)
           .WithMany(p => p.RelatedTickets)
           .HasForeignKey(pc => pc.FromId);
        builder.Entity<Relation>()
           .HasOne(c => c.TicketTo)
           .WithMany(p => p.RelatedTickets)
           .HasForeignKey(pc => pc.ToId);

但是结果是我有一个错误:

But in result i have an error:

无法在"Ticket.RelatedTickets"和 'Relation.TicketTo'，因为之间已经存在关系 "Ticket.RelatedTickets"和"Relation.TicketForm".导航 属性只能参与单个关系.

Cannot create a relationship between 'Ticket.RelatedTickets' and 'Relation.TicketTo', because there already is a relationship between 'Ticket.RelatedTickets' and 'Relation.TicketForm'. Navigation properties can only participate in a single relationship.

可能的解决方案是直接将父关系添加到TicketEntity:

The possible solution is to add Parent relation directly to TicketEntity:

public class Ticket
{ 
    public int Id { get; set; }

    [Required, ForeignKey("ParentRelation")]
    public Nullable<int> ParentRelationId { get; set; }

    public virtual Ticket ParentRelation {get;set;}

    public virtual ICollection<Ticket> RelatedTickets { get; set; }
    ...
}

使用这样的流利的api:

With fluent api like this:

modelBuilder.Entity<Ticket> =>
{
    entity
        .HasMany(e => e.RelatedTickets)
        .WithOne(e => e.ParentRelation) 
        .HasForeignKey(e => e.ParentRelationId );
});

但是存储这样的父关系看起来很肮脏".
什么是正确的方法?

But it looks 'dirty' to store parent relation like this.
What is the right approach?

推荐答案

不可能只有一个具有关系的集合.您需要两个-一个与票证等于TicketFrom的关系，第二个与票证等于TicketTo的关系.

It's not possible to have just one collection with relations. You need two - one with relations the ticket equals TicketFrom and second with relations the ticket equals TicketTo.

类似这样的东西:

型号:

public class Ticket
{ 
    public int Id { get; set; }
    public string Title { get; set; }

    public virtual ICollection<Relation> RelatedTo { get; set; }
    public virtual ICollection<Relation> RelatedFrom { get; set; }
}

public class Relation
{
    public int FromId { get; set; }
    public int ToId { get; set; }

    public virtual Ticket TicketFrom { get; set; }
    public virtual Ticket TicketTo { get; set; }
}

配置:

modelBuilder.Entity<Relation>()
    .HasKey(e => new { e.FromId, e.ToId });

modelBuilder.Entity<Relation>()
    .HasOne(e => e.TicketFrom)
    .WithMany(e => e.RelatedTo)
    .HasForeignKey(e => e.FromId);

modelBuilder.Entity<Relation>()
    .HasOne(e => e.TicketTo)
    .WithMany(e => e.RelatedFrom)
    .HasForeignKey(e => e.ToId);

请注意，使用父级的解决方案并不等效，因为它会创建one-to-many关联，而如果我理解正确，那么您正在寻找many-to-many.

Note that a solution using Parent is not equivalent, because it would create one-to-many association, while if I understand correctly you are seeking for many-to-many.

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