用于一对多关系的 EF Core 联接表

Question

我有以下类：User、Post 和 UserPost。 User 和 Post 是一对多的关系。 还有一个名为 UserPost 的第三个连接表，用于跟踪每个帖子获得的赞成/反对票。 为确保每个用户只能投票/否决一次，该表的 ID（PK）是 User 和 Post ID 的组合键。

public class User {
    public Guid Id {get; set;}
    public string UserName {get; set;}
    public ICollection<Post> Posts {get; set;}
}

public class Post {
    public Guid Id {get; set;}
    public string Content {get;set;}
    public User User {get; set;}
}

public UserPost {
    public Guid Id {get; set;} // This should be a composite key of User ID and Post ID
    public Guid PostId {get;set;}
    public Guid UserId {get;set;}
    public VoteType VoteType {get;  set;}
}

public enum VoteType {
    Up = 1,
    Down = 0
}

在我的数据库上下文 class 中，我定义了这样的用户/帖子关系：

builder.Entity<User>()
    .HasMany(u => u.Posts)
    .WithOne(p => p.User)

现在我想定义 UserPost model 的关系，但不知道如何 go 关于它。 到目前为止，我有：

builder.Entity<UserPost>()
   .HasKey(x => new { x.UserId, x.PostId })

还需要什么吗？

Answer 1

写下你的整个关系如下：

public class User 
{
    public Guid Id {get; set;}
    public string UserName {get; set;}
    public ICollection<Post> Posts {get; set;}
}

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

    public Guid UserId {get; set;}
    public User User {get; set;}
}

public UserVote // Rename this from UserPost to UserVote to keep naming consistency. 
{
    public Guid PostId {get;set;}
    public Guid UserId {get;set;}
    public VoteType VoteType {get;  set;}

    public Post Post {get; set;}
    public User User {get; set;}
}

public enum VoteType {
    Up = 1,
    Down = 0
}

现在，为 UserVote 配置Fluent API UserVote ：

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

   modelBuilder.Entity<UserVote>(e =>
   { 
       e.HasKey(uv => new { uv.PostId, uv.UserId}); //<-- Here is the composite key.
       e.HasOne(uv => uv.Post).WithMany().HasForeignKey(uv => uv.PostId).OnDelete(DeleteBehavior.Restrict);
       e.HasOne(uv => uv.User).WithMany().HasForeignKey(uv => uv.UserId).OnDelete(DeleteBehavior.Restrict);
   });
}