Question

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

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; }
}

History属性包含与该帖子相关的所有PostVersions的列表。 CurrentVersion和PreviousVersion属性均引用该帖子历史记录中的Perticlar版本（大多数likley是最新版本，是第一个版本）。

我的问题是，由于CurrentVersion和OriginalVersion导航属性，EF Core难以理解这种关系。当我尝试创建迁移时，出现以下错误消息：

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。

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.

是否可以先在EF Core代码中创建这种关系？

Answer 1

修改我做了一些更改，您不能在多个关系中引用同一属性。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 参考。

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);

原始您需要为第二个关系指定其他属性

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);

EFCore-如何具有相同类型的多个导航属性？

1 个答案: