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c# - 如何正确设置 ApplicationUser 和 FriendRequest 实体以允许级联删除

问题描述

我有传统的ApplicationUser（IdentityUser），该用户可以向另一个用户发送好友请求ApplicationUser。我目前有以下通用实体类：

public class ApplicationUser : IdentityUser
{
    public virtual List<DeviceToken> DeviceTokens { get; set; } = new List<DeviceToken>();
    public string DisplayName { get; set; }
}

public class FriendRequest
{
    public int Id { get; set; }
    public DateTime DateRequested { get; set; }
    public ApplicationUser Requester { get; set; }
    public ApplicationUser Receiver { get; set; }
}

我已经运行了数据库更新等，这工作正常。但是，当我进入我的 SQLServer 尝试删除 ApplicationUser 时，它告诉我The DELETE statement conflicted with the REFERENCE constraint "FK_FriendRequest_AspNetUsers_RequesterId".

所以我决定实现从 ApplicationUser 到他们所属的朋友请求的级联删除流程。

我已经尝试过微软在此处配置级联删除的资源，但我无法弄清楚如何将其应用于我的案例：

builder.Entity<ApplicationUser>()
    .HasMany(e => e.FriendRequests)//No such property, no idea how to address
    .OnDelete(DeleteBehavior.ClientCascade);

  1. 如何设置此级联删除方案？

  2. 另外，如何向 ApplicationUser 添加一个属性，该属性引用它们所属的所有 FriendRequest，并确保 EFCore 知道我指的是现有的 FriendRequest 实体/表？

更新

遵循向 ApplicationUser 添加虚拟属性的建议方法，这将是前进的方向：

public class ApplicationUser : IdentityUser
{
    public virtual List<DeviceToken> DeviceTokens { get; set; } = new List<DeviceToken>();
    public string DisplayName { get; set; }
    public ICollection<FriendRequest> FriendRequests { get; }
}

builder.Entity<ApplicationUser>()
    .HasMany(u => u.FriendRequests)
    .WithOne(u => u.Requester)
    .OnDelete(DeleteBehavior.ClientCascade); //not sure about this

builder.Entity<ApplicationUser>()
    .HasMany(u => u.FriendRequests)
    .WithOne(u => u.Requester)
    .OnDelete(DeleteBehavior.ClientCascade); //not sure about this

标签： c#entity-framework-core

解决方案

您的 ApplicationUser 需要 2 个虚拟 ICollections。

public class ApplicationUser 
{
    public int Id { get; set; }
    public string DisplayName { get; set; }
    public virtual ICollection<FriendRequest> FriendRequestsAsRequestor { get; set; }
    public virtual ICollection<FriendRequest> FriendRequestsAsReceiver { get; set; }
}

public class FriendRequest
{
    public int Id { get; set; }
    public DateTime DateRequested { get; set; }
    public int RequestorId { get; set; }
    public ApplicationUser Requestor { get; set; }
    public int ReceiverId { get; set; }
    public ApplicationUser Receiver { get; set; }
}

public class ApplicationUserConfig : IEntityTypeConfiguration<ApplicationUser>
{
    public void Configure(EntityTypeBuilder<ApplicationUser> builder)
    {
        builder.HasMany(au => au.FriendRequestsAsRequestor)
            .WithOne(fr => fr.Requestor)
            .HasForeignKey(fr => fr.RequestorId)
            .OnDelete(DeleteBehavior.Cascade);

        builder.HasMany(au => au.FriendRequestsAsReceiver)
            .WithOne(fr => fr.Receiver)
            .HasForeignKey(fr => fr.ReceiverId)
            .OnDelete(DeleteBehavior.Cascade);
    }
}

利用：

void AddFriendRequest(int requestorId, int receiverId)
{
    var ctxt = new DbContext();
    FriendRequest fr = new FriendRequest
    {
        RequestorId = requestorId;
        ReceiverId = receiverId;
        DateRequested = DateTime.Now;
    }

    ctxt.FriendRequests.Add(fr);
    ctxt.SaveChanges();
}

List<FriendRequest> GetFriendRequests()
{
    var ctxt = new DbContext();
    return ctxt.FriendRequests
        .Include(fr => fr.Requestor)
        .Include(fr => fr.Receiver)
        .ToList(); 
}

ApplicationUser GetUserWithFriendRequests(int id)
{
    var ctxt = new DbContext();
    return ctxt.ApplicationUser
        .Include(au => au.FriendRequestsAsRequestor)
        .Include(au => au.FriendRequestsAsReceiver)
        .SingleOrDefault(au => au.Id == id);
}

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