问题
How do you remove a HABTM associated item without deleting the item itself?
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.
I'm using JavaScript with drag-and-drop for adding and removing, not check boxes. Any thoughts?
回答1:
I tend to use has_many :through, but have you tried
student.classes.delete(science)
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
If you want the simplicity of HABTM you need to use
student.classes.delete(Class.find 2)
Also, calling a model "Class" is a really bad idea. Use a name that isn't part of the core of Ruby!
回答2:
If you want to delete multiple associated items you can use * and write:
student.classes.delete(*classes_array)
来源：https://stackoverflow.com/questions/1089892/how-do-i-remove-a-single-habtm-associated-item-without-deleting-the-item-itself