从多对多关系中仅删除一个条目 [英] Deleting only one entry from Many-to-Many relationship

问题描述

好，所以我现在有这个问题。我有2个像这样的模型：

Ok, so i have this problem right now. I have 2 Models like so:

public class Contact: BaseModel
    {

        public string LastName { get; set; }

        public string FirstMidName { get; set; }

        public string Adress { get; set; }
        public int UserID { get; set; }

        [Display(Name = "Full Name")]
        public string FullName
        {
            get
            {
                return FirstMidName+ " " + LastName;
            }
        }

        public virtual List<Group> Groups { get; set; }
        public virtual User User { get; set; }
        public virtual ICollection<Phones> Phones { get; set; }
    }

，并且：

public class Group:BaseModel
    {
        public string Name { get; set; }
        public int UserID { get; set; }
        public virtual User User { get; set; }
        public virtual List<Contact> Contacts { get; set; }

    }

这个想法是，许多联系人可以在多个组中。但是我的问题来了。我将公约ondeleteCascade删除了很多，因为我不得不否则我的代码将无法正常工作。但是...我如何只删除一个联系人...而无需级联并删除它的所有组中以及该组包含的所有联系人，依此类推。这就是我的问题，我希望能够删除一个联系人而不是一个群组。我不希望仅删除联系人。请帮忙

the idea is that many contacts can be in many groups. But here comes my problem. I remove the convention ondeleteCascade with many to many because i had to otherwise my code wouldnt work.But... how can i delete only one contact... without it cascading and deleting all the groups its in and all the contacts that group contains and so on and so forth. Thats my problem id love to be able to delete one contact not a group tho. i do not want the group to be deleted just the contact. Please help

推荐答案

您只需将级联删除选项保持为<

You should simply keep the cascade delete option turned on for that relationship.

在多对多链接，而不是实际的组实体。删除组时同样如此。

In the many-to-many relationship, none of the sides "owns" the other. Instead, the relationship is maintained by a third entity (hidden in your case) called "link" table, so for instance deleting a contact will simple delete the group links tied to that contact, not the actual group entities. The same applies when deleting a group.

编辑：尽管以上内容通常适用，但实际问题是由两个引起的。对多关系（ User->联系人和 User-> Group ）中未提及的问题，默认情况下级联删除将打开。这会导致经典的多个级联路径问题-删除 User 记录时，链接表 GroupContact 记录可以由 User-> Contact-> GroupContact 或 User-> Group-> GroupContact ，因此是多删除路径。

While the above applies in general, it turns out that the actual problem is caused by the two one-to-many relationships (User->Contact and User->Group) not mentioned in the question which by default has cascade delete turned on. Which leads to a classical multiple cascade paths issue - when deleting a User record, the link table GroupContact records can be deleted by either User->Contact->GroupContact or User->Group->GroupContact, hence is a multiple delete path.

因此，您必须至少打开 User-> Contact ，中的一个用户->组或联系人<->组关系级联删除。不幸的是，这将导致您的维护问题，因为您将无法简单地删除所涉及的实体之一。由于我猜您不是经常删除用户，因此建议您关闭 User-> Group 关系级联删除，然后手动删除相关的 User.Group ，然后删除 User 。或在数据库内的 User 表上放置一个删除触发器。

So you have to turn at least one of the User->Contact, User->Group or Contact<->Group relationship cascade delete off. Unfortunately that will cause you maintenance problems because you'll not be able to simple the delete one of the entities involved. Since I guess you are not deleting users so often, I would suggest you to turn User->Group relationship cascade delete off and manually delete the related User.Groups before deleting a User. Or put a delete trigger on the User table inside the database.

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