如何删除不删除项本身的单一HABTM相关的项目？ [英] How do I remove a single HABTM associated item without deleting the item itself?

问题描述

你如何删除HABTM相关的项目，而不删除项目本身？

How do you remove a HABTM associated item without deleting the item itself?

举例来说，假设我有3个学生是在科学类在一起。如何删除而不删除实际的科学参考科学从StudentsClasses表对象？我猜 Student.Classes.first.delete 是不是一个好主意。

For example, say I have 3 Students that are in a Science class together. How do I remove the Science objects from the StudentsClasses table without deleting the actual Science reference? I'm guessing that Student.Classes.first.delete isn't a good idea.

我使用的是拖和下降的JavaScript添加和移除，而不是复选框。有什么想法？

I'm using JavaScript with drag-and-drop for adding and removing, not check boxes. Any thoughts?

推荐答案

我倾向于使用的has_many：通过，但你试过

I tend to use has_many :through, but have you tried

student.classes.delete(science)

我觉得需要有目标对象，而不仅仅是ID，是HABTM的限制（因为连接表抽离为了您的方便）。如果您使用的has_many：通过您可以在连接表直接操作（因为你得到一个模型），并且让您优化这样的事情到较少的查询

I think needing to have the target object, not just the ID, is a limitation of HABTM (since the join table is abstracted away for your convenience). If you use has_many :through you can operate directly on the join table (since you get a Model) and that lets you optimize this sort of thing into fewer queries.

def leave_class(class_id)
  ClassMembership.delete(:all, :conditions => ["student_id = ? and class_id = ?", self.id, class_id)
end

如果你想HABTM的简单，你需要使用

If you want the simplicity of HABTM you need to use

student.classes.delete(Class.find 2)

此外，调用模型类是一个非常糟糕的主意。使用一个名称，是不是红宝石的核心的一部分！

Also, calling a model "Class" is a really bad idea. Use a name that isn't part of the core of Ruby!

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