c# - 使用 Entity Framework Code First 删除关系

Question

我使用 Entity Framework Code First 和最新的 Entity Framework 版本创建了自己的数据库模型。

我有这堂课：

[DataContract]
public class User
{
    [DataMember]
    public int UserId { get; set; }

    [DataMember]
    public string Name { get; set; }

    [DataMember]
    public int Age { get; set; }

    [DataMember]
    public string City { get; set; }

    [DataMember]
    public string Country { get; set; }

    [DataMember]
    public string Email { get; set; }

    [DataMember]
    public string InterestIn { get; set; }


    [DataMember]
    public virtual ICollection<User> Friends { get; set; }

    [DataMember]
    public virtual ICollection<User> FromWhomIsFriend { get; set; }

    [DataMember]
    public virtual ICollection<Activity> WantsToDo { get; set; }

    [DataMember]
    public virtual ICollection<Message> MessagesSent { get; set; }

    [DataMember]
    public virtual ICollection<Message> MessagesReceived { get; set; }

    public override string ToString()
    {
        string output = string.Empty;

        output = String.Format("UserId: {0}, Name: {1}, Age: {2}, City: {3}, " +
            "Country: {4}, Email: {5}, InterestIn: {6}",
            UserId, Name, Age, City, Country, Email, InterestIn);

        return output;
    }
}

及其配置类：

class UserConfiguration : EntityTypeConfiguration<User>
{
    public UserConfiguration()
    {
        Property(d => d.Name).IsRequired();
        Property(d => d.Age).IsRequired();
        Property(d => d.City).IsRequired();
        Property(d => d.Country).IsRequired();
        Property(d => d.Email).IsRequired();
        Property(d => d.InterestIn).IsRequired();

        HasMany(d => d.MessagesSent).WithRequired(l => l.SentByUser).WillCascadeOnDelete(false);
        HasMany(d => d.MessagesReceived).WithRequired(l => l.SentToUser).WillCascadeOnDelete(false);

        HasMany(d => d.Friends).
            WithMany(d => d.FromWhomIsFriend).
            Map(c =>
                {
                    c.ToTable("UserFriends");
                    c.MapLeftKey("UserId");
                    c.MapRightKey("FriendId");
                });
        HasMany(d => d.WantsToDo).
            WithMany(a => a.Users).
            Map(t =>
                {
                    t.ToTable("UserActivities");
                    t.MapLeftKey("UserId");
                    t.MapRightKey("ActivityId");
                });
    }
}

表示这种多对多自我关系：

现在我有一个问题：我不知道如何删除朋友关系。使用 SQL，我将执行以下操作：

DELETE FROM UserFriend
WHERE (userId = user1_id   AND friendId = friend1_id) OR
      (userId = friend1_id AND friendId = user1_id)

user1_id：是要删除好友关系的用户。 friend1_id: 是 user1 想要删除为好友的好友。

我该怎么做？

Answer 1

所以，如果我理解正确，如果用户 User1 是 User2 的朋友，那么关系将是 inuser1.Friends或 in user1.FromWhomIsFriend。

您应该检查关系在哪里，并相应地删除它。

 public void RemoveFriend(User user, User friend)
 {
   if (user1.Friends.Contains(friend));
      user1.Friends.Remove(friend);
   if (user1.FromWhomIsFriend.Contains(friend));
      user1.FromWhomIsFriend.Remove(friend);
 }

Answer 2

只需从集合中删除朋友：

user.Friends.Remove(friendToRemove);