关系贝特文实体模型的问题

Question

我想在我的项目中制作一个“喜欢”和“不喜欢”系统，我有一个用户模型，一个帖子模型，一个评论模型，其关系如下：

用户 1 ---> * 帖子

用户 1 ---> * 评论

帖子 1 ---> * 评论

现在我想添加一个名为“喜欢”的新模型，其关系如下：

发布 1 ---> * 赞用户 1 ---> * 赞

但是当我想更新数据库时，我收到一个错误，说：“可能导致循环或多个级联路径”，我发现如果我删除我的一个属性，它会修复错误，例如：

public class Post

{

    public Post()

    {

    }

    [Key]

    public int Id { get; set; }

    public string Title { get; set; }

    public virtual List<Like> Likes { get; set; }

    public virtual List<Comment> Comments { get; set; }

}

public class Like

{

    public Like()

    {

    }

    [Key]

    public int Id { get; set; }

    public bool IsLike { get; set; }

    public int postId { get; set; } // I remove these properties

    public virtual Post post { get; set; }

    public int commentId { get; set; }  // I remove these properties

    public virtual Comment comment { get; set; }

}

为了修复“多个级联”错误，我删除了“PostId”和“commentId”属性。

但是当我在数据库中将实体（新数据）添加到我的表（Like）中时，我不知道我的帖子是如何重复的，我的意思是重复的帖子被添加到表中。

任何人都可以告诉我问题吗？

Answer 1

问题是，您的数据库不够规范化。我看到用户可以创建.他们也可以在 a 上发表评论。PostsCommentPostLike因为 a 是 a，所以 a on this 自动成为 a on 注释是关于CommentComment about a PostLikeCommentLikePost换句话说：如果有人创建了关于帖子（10）的评论（4），那么为评论（4）和帖子（20）创建赞是荒谬的。评论（4）与帖子（20）无关！每个赞都是由一个用户创建的，恰好是关于一个评论的。用户创建零个或多个赞（一对多），并且评论已被赞零次或多次（也是一对多）因此，您有以下一系列操作：用户 1 创建帖子 10：帖子 10 具有外键 CreateByUserId 1用户 2 创建有关帖子 10 的评论 20。Comment 20 已 CommentByUserId 2 和 PostId 20用户 3 喜欢评论 20.Like 30 有 LikedByUserId 3 和 CommentId 20这对于实体框架来说已经足够规范化了。为了使关系更清晰，我稍微更改了一下外键。class User{&nbsp; &nbsp; &nbsp;public int Id {get; set;}&nbsp; &nbsp; &nbsp;...&nbsp; &nbsp; &nbsp;// Every User creates zero or more Posts (one-to-many)&nbsp; &nbsp; &nbsp;public virtual ICollection<Post> Posts {get; set;}&nbsp; &nbsp; &nbsp;// Every User creates zero or more Comments (one-to-many)&nbsp; &nbsp; &nbsp;public virtual ICollection<Comment> Comments {get; set;}&nbsp; &nbsp; &nbsp;// Every User creates zero or more Likes (one-to-many)&nbsp; &nbsp; &nbsp;public virtual ICollection<Like> Likes {get; set;}}class Post{&nbsp; &nbsp; public int Id {get; set;}&nbsp; &nbsp; ...&nbsp; &nbsp; // Every Post is posted by exactly one User, using foreign key&nbsp; &nbsp; public int PostedByUserId {get; set;}&nbsp; &nbsp; public User User {get; set;}&nbsp; &nbsp; // Every Post has zero or more Comments (one-to-many)&nbsp; &nbsp; public virtual ICollection<Comment> Comments {get; set;}}和类评论和喜欢：class Comment{&nbsp; &nbsp; public int Id {get; set;}&nbsp; &nbsp; ...&nbsp; &nbsp; // Every Comment is posted by exactly one User, using foreign key&nbsp; &nbsp; public int CommentedByUserId {get; set;}&nbsp; &nbsp; public virtual User User {get; set;}&nbsp; &nbsp; // Every Comment is about exactly one Post, using foreign key&nbsp; &nbsp; public int PostId {get; set;}&nbsp; &nbsp; public virtual Post Post {get; set;}&nbsp; &nbsp; // Every Comment has zero or more Likes (one-to-many)&nbsp; &nbsp; public virtual ICollection<Like> Likes {get; set;}}class Like{&nbsp; &nbsp; public int Id {get; set;}&nbsp; &nbsp; ...&nbsp; &nbsp; // Every Like is created by exactly one User, using foreign key&nbsp; &nbsp; public int LikedByUserId {get; set;}&nbsp; &nbsp; public virtual User User {get; set;}&nbsp; &nbsp; // Every Like is about exactly one Comment, using foreign key&nbsp; &nbsp; public int CommentId {get; set;}&nbsp; &nbsp; public virtual Comment Comment {get; set;}}因为我的外键偏离了约定，所以我需要使用 Fluent API 通知实体框架有关这些外键的信息：帖子具有用户的外键：modelBuilder.Entity<Post>()&nbsp; &nbsp; .HasRequired(post => post.User)&nbsp; &nbsp; .WithMany(user => user.Posts)&nbsp; &nbsp; .HasForeignKey(post => post.CreatedByUserId);评论有外键到用户和帖子：var commentEntity = modelBuilder.Entity<Comment>();commentEntity.HasRequired(comment => comment.User)&nbsp; &nbsp; .WithMany(user => user.Comments)&nbsp; &nbsp; .HasForeignKey(comment => comment.CommentedByUserId);commentEntity.HasRequired(comment => comment.Post)&nbsp; &nbsp; .WithMany(post => post.Comments)&nbsp; &nbsp; .HasForeignKey(comment => comment.PostId);Like 有外键到用户和注释：var likeEntity = modelBuilder.Entity<Like>();likeEntity.HasRequired(like => like.User)&nbsp; &nbsp; .WithMany(user => user.Likes)&nbsp; &nbsp; .HasForeignKey(like => like.LikedByUserId);likeEntity.HasRequired(like&nbsp; => like.Comment)&nbsp; &nbsp; .WithMany(comment => comment.Likes)&nbsp; &nbsp; .HasForeignKey(like => like.CommentId);如果将来你想给用户提供喜欢帖子而不是评论的可能性，或者像用户一样，关系将非常相似。首先给用户正确的（每个用户都喜欢零个或多个...），你将自动知道在哪里放置外键virtual ICollection<...>

Answer 2

为了更好的设计，请将 like 表分开，如下所示：PostCommentpublic class User{&nbsp; &nbsp; [Key]&nbsp; &nbsp; public int Id { get; set; }&nbsp; &nbsp; //......&nbsp; &nbsp; public virtual List<Post> Posts { get; set; }&nbsp; &nbsp; public virtual List<Comment> Comments { get; set; }&nbsp; &nbsp; public virtual List<PostLikes> PostLikes { get; set; }&nbsp; &nbsp; public virtual List<CommentLIkes> CommentLikes { get; set; }}public class Post{&nbsp; &nbsp; [Key]&nbsp; &nbsp; public int Id { get; set; }&nbsp; &nbsp; public string Title { get; set; }&nbsp; &nbsp; public virtual List<PostLike> PostLikes { get; set; }&nbsp; &nbsp; public virtual List<Comment> Comments { get; set; }}public class Comment{&nbsp; &nbsp; [Key]&nbsp; &nbsp; public int Id { get; set; }&nbsp; &nbsp; public string CommentBody { get; set; }&nbsp; &nbsp; //.....&nbsp; &nbsp; public virtual List<CommentLike> CommentLikes { get; set; }}public class PostLike{&nbsp; &nbsp; [Key]&nbsp; &nbsp; public int Id { get; set; }&nbsp; &nbsp; public int PostId { get; set; }&nbsp; &nbsp; public int UserId {get; set;}&nbsp; &nbsp; public bool IsLike { get; set; }&nbsp; &nbsp; public virtual Post post { get; set; }&nbsp; &nbsp; public virtual User User { get; set; }}public class CommentLike{&nbsp; &nbsp; [Key]&nbsp; &nbsp; public int Id { get; set; }&nbsp; &nbsp; public int CommentId { get; set; }&nbsp; &nbsp; public int UserId {get; set;}&nbsp; &nbsp; public bool IsLike { get; set; }&nbsp; &nbsp; public virtual Comment Comment { get; set; }&nbsp; &nbsp; public virtual User User { get; set; }}现在生成一个全新的迁移并相应地更新数据库。注意：在迁移更新时，您可能会遇到级联删除问题。如果您遇到让我知道，我将使用Fluent API配置更新答案。