实体框架核心：如何解决？引入外键约束可能会导致循环或多个级联路径 [英] Entity Framework Core: How to solve Introducing FOREIGN KEY constraint may cause cycles or multiple cascade paths

问题描述

我正在使用带有Code First方法的Entity Framework Core，但在更新数据库时收到以下错误：

I'm using Entity Framework Core with Code First approach but recieve following error when updating the database:

引入FOREIGN KEY约束'表'AnEventUsers'上的FK_AnEventUsers_Users_UserId'可能会导致循环或多个级联路径。指定ON DELETE NO ACTION或ON UPDATE NO ACTION，或修改其他FOREIGN KEY约束。
无法创建约束或索引。请参阅先前的错误。

Introducing FOREIGN KEY constraint 'FK_AnEventUsers_Users_UserId' on table 'AnEventUsers' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints. Could not create constraint or index. See previous errors.

我的实体是：

public class AnEvent
{
    public int AnEventId { get; set; }
    public DateTime Time { get; set; }
    public Gender Gender { get; set; }
    public int Duration { get; set; }
    public Category Category { get; set; }
    public int MinParticipants { get; set; }
    public int MaxParticipants { get; set; }
    public string Description { get; set; }
    public Status EventStatus { get; set; }
    public int MinAge { get; set; }
    public int MaxAge { get; set; }
    public double Longitude { get; set; }
    public double Latitude { get; set; }

    public ICollection<AnEventUser> AnEventUsers { get; set; }

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


public class User
{
    public int UserId { get; set; }
    public int Age { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public Gender Gender { get; set; }
    public double Rating { get; set; }

    public ICollection<AnEventUser> AnEventUsers { get; set; }
}

public class AnEventUser
{
    public int AnEventId { get; set; }
    public AnEvent AnEvent { get; set; }

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

}

public class ApplicationDbContext:DbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options):base(options)
    { }


    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<AnEventUser>()
            .HasOne(u => u.User).WithMany(u => u.AnEventUsers).IsRequired().OnDelete(DeleteBehavior.Restrict);


        modelBuilder.Entity<AnEventUser>()
            .HasKey(t => new { t.AnEventId, t.UserId });

        modelBuilder.Entity<AnEventUser>()
            .HasOne(pt => pt.AnEvent)
            .WithMany(p => p.AnEventUsers)
            .HasForeignKey(pt => pt.AnEventId);

        modelBuilder.Entity<AnEventUser>()
            .HasOne(eu => eu.User)
            .WithMany(e => e.AnEventUsers)
            .HasForeignKey(eu => eu.UserId);

    }

    public DbSet<AnEvent> Events { get; set; }
    public DbSet<User> Users { get; set; }
    public DbSet<AnEventUser> AnEventUsers { get; set; }
}

我认为的问题是，如果我们删除用户，则对AnEvent将被删除，并且对AnEventUser的引用也将被删除，因为AnEvent中也有对AnEventUser的引用，因此我们得到了级联路径。但是我使用以下命令从User到AnEventUser中删除了删除级联：

The issue I thought was that if we delete a User the reference to the AnEvent will be deleted and also the reference to AnEventUser will also be deleted, since there is a reference to AnEventUser from AnEvent as well we get cascading paths. But I remove the delete cascade from User to AnEventUser with:

 modelBuilder.Entity<AnEventUser>()
        .HasOne(u => u.User).WithMany(u => u.AnEventUsers).IsRequired().OnDelete(DeleteBehavior.Restrict);

但是错误无法解决，有人看到错了吗？谢谢！

But the error doesn't get resolved, does anyone see what is wrong? Thanks!

推荐答案

在 OnModelCreating 的示例代码中，您声明了 modelBuilder.Entity< AnEventUser>（）。HasOne（e => e.User）... 两次：在方法开头和结尾。

In your sample code in OnModelCreating you have declared modelBuilder.Entity<AnEventUser>().HasOne(e => e.User)... twice: at start of method and at end.

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<AnEventUser>()       // THIS IS FIRST
        .HasOne(u => u.User).WithMany(u => u.AnEventUsers).IsRequired().OnDelete(DeleteBehavior.Restrict);


    modelBuilder.Entity<AnEventUser>()
        .HasKey(t => new { t.AnEventId, t.UserId });

    modelBuilder.Entity<AnEventUser>()
        .HasOne(pt => pt.AnEvent)
        .WithMany(p => p.AnEventUsers)
        .HasForeignKey(pt => pt.AnEventId);

    modelBuilder.Entity<AnEventUser>()       // THIS IS SECOND.
        .HasOne(eu => eu.User)               // THIS LINES
        .WithMany(e => e.AnEventUsers)       //   SHOULD BE
        .HasForeignKey(eu => eu.UserId);     //   REMOVED

}

第二个呼叫优先。删除它。

Second call overrides first. Remove it.

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