创建用户关系表

Question

我想在ASP.NET Core中创建用户关系表并遇到一些问题。如果因为这个原因必须禁用级联删除，我该如何防止孤儿？

错误：

Introducing FOREIGN KEY constraint 'FK_UserRelationships_AspNetUsers_User2Id' on table 'UserRelationships' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints. 

ApplicationDbContext.cs：

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

    protected override void OnModelCreating(ModelBuilder builder) 
    { 
     base.OnModelCreating(builder); 
     builder.Entity<UserRelationship>().HasKey(x => new { x.User1Id, x.User2Id }); 
    } 

    public DbSet<UserRelationship> UserRelationships { get; set; } 
} 

我目前的模型：

public class UserRelationship 
{ 
    public byte RelationshipType { get; set; } 
    public ApplicationUser User1 { get; set; } 
    public string User1Id { get; set; } 
    public ApplicationUser User2 { get; set; } 
    public string User2Id { get; set; } 
} 

Answer 1

你有你的ApplicationUsers根据需要使EF将级联默认情况下删除两次到同一班（见here）。

你需要告诉它不要：

builder.Entity<UserRelationship>().HasOne(ur => ur.User1).WithMany().HasForeignKey(ur => ur.UserId1).WillCascadeOnDelete(false); 

builder.Entity<UserRelationship>().HasOne(ur => ur.User2).WithMany().HasForeignKey(ur => ur.UserId2).WillCascadeOnDelete(false);