floof/model/comments.py

   1 import datetime
   2
   3 from elixir import *
   4 from sqlalchemy import func
   5
   6 class Discussion(Entity):
   7     """Represents a collection of comments attached to some other object."""
   8     count = Field(Integer)
   9     comments = OneToMany('Comment', order_by='left')
  10
  11 class Comment(Entity):
  12     time = Field(DateTime, default=datetime.datetime.now)
  13     text = Field(Unicode(65536))
  14
  15     # Comments are a tree, and are stored as a nested set, because:
  16     # - It's easy to get a subtree with a single query.
  17     # - It's easy to get a comment's depth.
  18     # - It's easy to sort comments without recursion.
  19     # The only real disadvantage is that adding a comment requires a quick
  20     # update of all the following comments (in post-order), but that's rare
  21     # enough that it shouldn't be a problem.
  22     left = Field(Integer, index=True)
  23     right = Field(Integer)
  24
  25     discussion = ManyToOne('Discussion')
  26     user = ManyToOne('User')
  27
  28     def __init__(self, parent=None, **kwargs):
  29         """Constructor override to set left/right correctly on a new comment.
  30         """
  31         super(Comment, self).__init__(**kwargs)
  32
  33         # Keep the comment count updated
  34         self.discussion.count += 1
  35
  36         if parent:
  37             # Parent comment given.  Add this comment just before the parent's
  38             # right side...
  39             self.left = parent.right
  40             self.right = parent.right + 1
  41
  42             # ...then adjust all rightward comments accordingly
  43             Comment.query.filter(Comment.discussion == self.discussion) \
  44                          .filter(Comment.right > parent.right) \
  45                          .update({ Comment.left:  Comment.left + 2,
  46                                    Comment.right: Comment.right + 2 })
  47
  48             # And, finally, update the parent's right endpoint
  49             parent.right += 2
  50
  51         else:
  52             query = session.query(func.max(Comment.right)) \
  53                            .filter(Comment.discussion == self.discussion)
  54             (max_right,) = query.one()
  55
  56             if not max_right:
  57                 # No comments yet.  Use 1 and 2
  58                 self.left = 1
  59                 self.right = 2
  60             else:
  61                 self.left = max_right + 1
  62                 self.right = max_right + 2