EFCore-如何使多个导航属性具有相同的类型？ [英] EFCore - How to have multiple navigation properties to the same type?

问题描述

我的模型包含Post和PostHistory类，其中Post与PostHistory具有一对多关系。

My model contains the classes Post and PostHistory, where Post has a one-to-many relationship with PostHistory.

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

    public PostVersion CurrentVersion { get; set; }
    public PostVersion OriginalVersion { get; set; }
    public IList<PostVersion> History { get; set; }
}

class PostVersion
{
    public int Id { get; set; }
    public Post Post { get; set; }

    public string Title { get; set; }
    public string Body { get; set; }
}

历史记录属性包含与该帖子相关的所有PostVersions的列表。

The History property contains a list of all PostVersions related to that Post. The CurrentVersion and PreviousVersion properties both reference a perticlar version in that post history (most likley the most recent version and the first version).

我的问题是，EF Core难以解决这一问题。CurrentVersion和PreviousVersion属性都引用了该发布历史中的Perticlar版本（大多数likley是最新版本和第一个版本）。了解由于CurrentVersion和OriginalVersion导航属性引起的关系。当我尝试创建迁移时，收到以下错误消息：

My problem is that EF Core struggles to understand the relationship due to the CurrentVersion and OriginalVersion navigation properties. When I try to create a migration, I get this error message:

Unable to determine the relationship represented by navigation property 'Post.CurrentVersion' of type 'PostVersion'. Either manually configure the relationship, or ignore this property using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.

之后，我尝试使用Fluent API手动创建关系。

After that I tried to use the Fluent API to create the relationships manually.

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

    builder.Entity<Post>()
        .HasMany(x => x.History)
        .WithOne(x => x.Post);
    builder.Entity<Post>()
        .HasOne(x => x.CurrentVersion)
        .WithOne(x => x.Post);
    builder.Entity<Post>()
        .HasOne(x => x.OriginalVersion)
        .WithOne(x => x.Post);
}

但创建了另一个错误：

Cannot create a relationship between 'PostVersion.Post' and 'Post.CurrentVersion', because there already is a relationship between 'Post.History' and 'PostVersion.Post'. Navigation properties can only participate in a single relationship.

是否可以在EF Core代码优先的情况下创建这种关系？

Is it possible to create this kind of relationship in EF Core code-first?

推荐答案

编辑
我做了一些更改，无法在多个关系中引用相同的属性。因此，我不得不使用外键进行映射。 PostVersion 仅具有一个您需要的 Post 引用。

Edit I did some changes, you cannot reference same property in multiple relationships. Therefore i had to use foreign keys for mappings. PostVersion has only one Post reference as you required.

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

    public Guid CurrentVersionId { get; set; }
    public PostVersion CurrentVersion { get; set; }
    public Guid OriginalVersionId { get; set; }
    public PostVersion OriginalVersion { get; set; }
    public IList<PostVersion> History { get; set; }
}

public class PostVersion
{
    public Guid Id { get; set; }
    public Guid PostId { get; set; }

    public Post Post { get; set; }

    public string Title { get; set; }
    public string Body { get; set; }
}

modelBuilder.Entity<Post>()
    .HasOne(x => x.CurrentVersion)
    .WithOne()
    .HasForeignKey<Post>(p => p.CurrentVersionId);
modelBuilder.Entity<Post>()
    .HasOne(x => x.OriginalVersion)
    .WithOne()
    .HasForeignKey<Post>(p => p.OriginalVersionId);

modelBuilder.Entity<Post>()
    .HasMany(x => x.History)
    .WithOne(p => p.Post)
    .HasForeignKey(pv => pv.PostId);

---

原始
您需要为第二种关系指定其他财产

---

Original You need to specify additional property for that second relationship

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

    public PostVersion CurrentVersion { get; set; }
    public PostVersion OriginalVersion { get; set; }
    public IList<PostVersion> History { get; set; }
}

public class PostVersion
{
    public Guid Id { get; set; }
    public Post Post { get; set; }
    public Post SecondPost { get; set; }
    public Post ThirdPost { get; set; }

    public string Title { get; set; }
    public string Body { get; set; }
}


 modelBuilder.Entity<Post>()
            .HasOne(x => x.CurrentVersion)
            .WithOne(x => x.Post);
 modelBuilder.Entity<Post>()
            .HasOne(x => x.OriginalVersion)
            .WithOne(x => x.SecondPost);
 modelBuilder.Entity<Post>()
            .HasMany(x => x.History)
            .WithOne(x => x.ThirdPost);

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