Proposal for Better HistoryTracker storage schema

[johnnyshields]

I have a use case to build a human-readable audit trail. I find the association chain syntax to be difficult to work with. I'd propose to combine :modified, :action, and :association_chain into one tree structure.

Assuming we have these models:

class Post
  ...
  field :p1
  field :p2
  embeds_many :comments
  embeds_one :section
end

class Comment
  ...
  field :c1
  field :c2
  embeds_many :links 
end

class Link
  ...
  field :l1
end

class Section
  ...
  field :s1
end

Doing an edit might generate:

modified: {
  _action: :update,
  _version: 2,
  _id: '#P1',
  p1: ___,
  p2: ___,
  comments: [{
    _id: '#C1',
    _action: :update,
    _version: 2,
    c1: ___,
    c2: ___
  },{
    _id: '#C2',
    _action: :create,
    _version: 1,
    c1: ___,
    links: [{
      _id: '#L1',
      _action: :create,
      _version: 1,
      l1: ___
    }]
  }],
  section: {
    _id: '#S2',
    _action: :delete,
    _version: 2,
    s1: ___
  }
}

If I modify only an embedded model, the audit should still save from the parent downward:

modified: {
  _action: :update,
  _id: '#P1',
  _version: 3,
  comment: [{
    _id: '#C2',
    _action: :update,
    _version: 2,
    links: [{
      _id: '#L1',
      _action: :update,
      _version: 2,
      l1: ___
    }]
  }]
}

A drawback is that this structure makes it slightly difficult to follow history on embedded models. We may want to support "breakout mode" to where you can force embedded updates to be stored on a separately from their parents (i.e. the current structure).

[aq1018]

I'm not entirely clear on what you mean, but I'm going to assume that you want to save the entire document including the parent when a child document is modified.

Here is a bit of the background on why I used 'breakout mode'. This is to support "multi-user out-of-order undo". Meaning, many users can be undoing changes on a parent and its children in non-chronological order, the result should still be consistent. You can essentially undo an edit 10 versions before ( say removing an incorrect tag ), without discarding the latest 9 changes. These changes could be users slowly adding desired tags over time or users adding / modifying comments or sections on the parent.)

I think if we save the entire document into the tracker, then undo must be sequential.

[aq1018]

Basically this gem was originally designed to support a type of undo model called multi-user non-linear undo. See: http://en.wikipedia.org/wiki/Undo