floof/model/comments.py

   1 import datetime
   2
   3 from elixir import *
   4 from sqlalchemy import func
   5
   6 ### Utility function(s)
   7
   8 def indent_comments(comments):
   9     """Given a list of comment objects, returns the same comments (and changes
  10     them in-place) with an `indent` property set on each comment.  This
  11     indicates how deeply nested each comment is, relative to the first comment.
  12     The first comment's indent level is 0.
  13
  14     The comments must be a complete subtree, ordered by their `left` property.
  15
  16     This function will also cache the `parent` property for each comment.
  17     """
  18
  19     last_comment = None
  20     indent = 0
  21     right_ancestry = []
  22     for comment in comments:
  23         # If this comment is a child of the last, bump the nesting level
  24         if last_comment and comment.left < last_comment.right:
  25             indent = indent + 1
  26             # Remember current ancestory relevant to the root
  27             right_ancestry.append(last_comment)
  28
  29         # On the other hand, for every nesting level this comment may have just
  30         # broken out of, back out a level
  31         for i in xrange(len(right_ancestry) - 1, -1, -1):
  32             if comment.left > right_ancestry[i].right:
  33                 indent = indent - 1
  34                 right_ancestry.pop(i)
  35
  36         # Cache parent comment
  37         if len(right_ancestry):
  38             comment._parent = right_ancestry[-1]
  39
  40         comment.indent = indent
  41
  42         last_comment = comment
  43
  44     return comments
  45
  46
  47 ### Usual database classes
  48
  49 class Discussion(Entity):
  50     """Represents a collection of comments attached to some other object."""
  51     count = Field(Integer)
  52     comments = OneToMany('Comment', order_by='left')
  53
  54 class Comment(Entity):
  55     time = Field(DateTime, default=datetime.datetime.now)
  56     text = Field(Unicode(65536))
  57
  58     # Comments are a tree, and are stored as a nested set, because:
  59     # - It's easy to get a subtree with a single query.
  60     # - It's easy to get a comment's depth.
  61     # - It's easy to sort comments without recursion.
  62     # The only real disadvantage is that adding a comment requires a quick
  63     # update of all the following comments (in post-order), but that's rare
  64     # enough that it shouldn't be a problem.
  65     left = Field(Integer, index=True)
  66     right = Field(Integer)
  67
  68     discussion = ManyToOne('Discussion')
  69     user = ManyToOne('User')
  70
  71     def __init__(self, parent=None, **kwargs):
  72         """Constructor override to set left/right correctly on a new comment.
  73         """
  74         super(Comment, self).__init__(**kwargs)
  75
  76         # Keep the comment count updated
  77         self.discussion.count += 1
  78
  79         if parent:
  80             # Parent comment given.
  81             parent_right = parent.right
  82             # Shift every left/right ahead by two to make room for the new
  83             # comment's left/right
  84             Comment.query.filter(Comment.discussion == self.discussion) \
  85                          .filter(Comment.left >= parent_right) \
  86                          .update({ 'left': Comment.left + 2 })
  87             Comment.query.filter(Comment.discussion == self.discussion) \
  88                          .filter(Comment.right >= parent_right) \
  89                          .update({ 'right': Comment.right + 2 })
  90
  91             # Then stick the new comment in the right place
  92             self.left = parent_right
  93             self.right = parent_right + 1
  94
  95         else:
  96             query = session.query(func.max(Comment.right)) \
  97                            .filter(Comment.discussion == self.discussion)
  98             (max_right,) = query.one()
  99
 100             if not max_right:
 101                 # No comments yet.  Use 1 and 2
 102                 self.left = 1
 103                 self.right = 2
 104             else:
 105                 self.left = max_right + 1
 106                 self.right = max_right + 2
 107
 108     @property
 109     def parent(self):
 110         """Returns this comment's parent.  This is cached, hence its being a
 111         property and not a method.
 112         """
 113         if not hasattr(self, '_parent'):
 114             self._parent = Comment.query \
 115                 .filter(Comment.discussion_id == self.discussion_id) \
 116                 .filter(Comment.left < self.left) \
 117                 .filter(Comment.right > self.right) \
 118                 .order_by(Comment.left.desc()) \
 119                 .first()
 120         return self._parent