rails：has_many association：验证对数组的访问的最佳实践

Question

I'm pretty new to ruby and ruby-on-rails, so I need to learn best practices.

I have Tag model, each tag can have many sub-tags and many super-tags:

  has_many :super_tags, :through => :tag_hier_rels,         :source => :super_tag
  has_many :sub_tags,   :through => :reverse_tag_hier_rels, :source => :sub_tag

  has_many :tag_hier_rels,         :foreign_key => "sub_tag_id"
  has_many :reverse_tag_hier_rels, :foreign_key => "super_tag_id", :class_name => "TagHierRel"

I need to prevent user to create circular references. But with auto-generated methods :super_tags and :sub_tags I can't do this: everyone can do something like:

tag.super_tags.push another_tag , and I have no control on this. Rails validation mechanism isn't useful here: this mechanism prevents user to save invalid objects to database, but I need to prevent him even to modify object incorrectly: if I have circular reference, and I need to get all the sub-tags or super-tags recursively, I will run into stack overflow.

So I have done the following:

Declared these associations as private ones:

private :sub_tags=,   :sub_tags
private :super_tags=, :super_tags

Added methods with _copy postfix:

def sub_tags_copy
  return sub_tags.clone
end

def super_tags_copy
  return super_tags.clone
end

And added methods that actualy modify arrays:

  def sub_tags_push(tag)
    sub_tags.push tag if !self.all_sub_tags.include? tag and !self.all_super_tags.include? tag
  end

  def super_tags_push(tag)
    super_tags.push tag if !self.all_sub_tags.include? tag and !self.all_super_tags.include? tag
  end

  # TODO: more methods (at least we need to remove tags)

(methods all_sub_tags and all_super_tags generate arrays recursively)

It works, but I don't really like this solution: at least, it's not obvious for user that he should use ..._copy methods.

Probably I am doing this wrong?

UPD:

Or, is it bad practice in general to disallow user to change an object in wrong way? Probably I should allow user to change an object in wrong way, but only validate it before saving?

At least, I already figured out that it's hard to supply error messages if user does something wrong: currently, model just silently does not modify an object, and no error message is generated. I have to implement my own error messages engine, and this fact is an evidence that approach is really bad... I seem to struggle against the framework instead of using it.

Answer 1

You are always referring to user where you mean programmers ?

If that is the case, you should try to assert this kind of stuff through

1. Education (developer to developer)
2. Validation (via tests or rails validations)
3. Constraints (on the database level through db constraints or triggers)

I would try to do it top down.