+
−from google.appengine.ext import db
+
−import string
+
−    
+
−class Tag(db.Model):
+
−    "Google AppEngine model for store of tags."
+
−    
+
−    tag = db.StringProperty(required=True)
+
−    "The actual string value of the tag."
+
−    
+
−    added = db.DateTimeProperty(auto_now_add=True)
+
−    "The date and time that the tag was first added to the datastore."
+
−    
+
−    tagged = db.ListProperty(db.Key)
+
−    "A List of db.Key values for the datastore objects that have been tagged with this tag value."
+
−    
+
−    tagged_count = db.IntegerProperty(default=0)
+
−    "The number of entities in tagged."
+
−
+
−    @classmethod
+
−    def __key_name(cls, tag_name):
+
−        return cls.__name__ + '_' + tag_name
+
−    
+
−    def remove_tagged(self, key):
+
−        def remove_tagged_txn():
+
−            if key in self.tagged:
+
−                self.tagged.remove(key)
+
−                self.tagged_count -= 1
+
−                self.put()
+
−        db.run_in_transaction(remove_tagged_txn)
+
−        self.__class__.expire_cached_tags()
+
−
+
−    def add_tagged(self, key):
+
−        def add_tagged_txn():
+
−            if key not in self.tagged:
+
−                self.tagged.append(key)
+
−                self.tagged_count += 1
+
−                self.put()
+
−        db.run_in_transaction(add_tagged_txn)
+
−        self.__class__.expire_cached_tags()
+
−    
+
−    def clear_tagged(self):
+
−        def clear_tagged_txn():
+
−            self.tagged = []
+
−            self.tagged_count = 0
+
−            self.put()
+
−        db.run_in_transaction(clear_tagged_txn)
+
−        self.__class__.expire_cached_tags()
+
−        
+
−    @classmethod
+
−    def get_by_name(cls, tag_name):
+
−        return cls.get_by_key_name(cls.__key_name(tag_name))
+
−    
+
−    @classmethod
+
−    def get_tags_for_key(cls, key):
+
−        "Set the tags for the datastore object represented by key."
+
−        tags = db.Query(cls).filter('tagged =', key).fetch(1000)
+
−        return tags
+
−    
+
−    @classmethod
+
−    def get_or_create(cls, tag_name):
+
−        "Get the Tag object that has the tag value given by tag_value."
+
−        tag_key_name = cls.__key_name(tag_name)
+
−        existing_tag = cls.get_by_key_name(tag_key_name)
+
−        if existing_tag is None:
+
−            # The tag does not yet exist, so create it.
+
−            def create_tag_txn():
+
−                new_tag = cls(key_name=tag_key_name, tag=tag_name)
+
−                new_tag.put()
+
−                return new_tag
+
−            existing_tag = db.run_in_transaction(create_tag_txn)
+
−        return existing_tag
+
−    
+
−    @classmethod
+
−    def get_tags_by_frequency(cls, limit=1000):
+
−        """Return a list of Tags sorted by the number of objects to which they have been applied,
+
−        most frequently-used first.  If limit is given, return only that many tags; otherwise,
+
−        return all."""
+
−        tag_list = db.Query(cls).filter('tagged_count >', 0).order("-tagged_count").fetch(limit)
+
−            
+
−        return tag_list
+
−
+
−    @classmethod
+
−    def get_tags_by_name(cls, limit=1000, ascending=True):
+
−        """Return a list of Tags sorted alphabetically by the name of the tag.
+
−        If a limit is given, return only that many tags; otherwise, return all.
+
−        If ascending is True, sort from a-z; otherwise, sort from z-a."""
+
−
+
−        from google.appengine.api import memcache
+
−
+
−        cache_name = cls.__name__ + '_tags_by_name'
+
−        if ascending:
+
−            cache_name += '_asc'
+
−        else:
+
−            cache_name += '_desc'
+
−            
+
−        tags = memcache.get(cache_name)
+
−        if tags is None or len(tags) < limit:
+
−            order_by = "tag"
+
−            if not ascending:
+
−                order_by = "-tag"
+
−            
+
−            tags = db.Query(cls).order(order_by).fetch(limit)
+
−            memcache.add(cache_name, tags, 3600)
+
−        else:
+
−            if len(tags) > limit:
+
−                # Return only as many as requested.
+
−                tags = tags[:limit]
+
−                
+
−        return tags
+
−        
+
−    
+
−    @classmethod
+
−    def popular_tags(cls, limit=5):
+
−        from google.appengine.api import memcache
+
−        
+
−        tags = memcache.get(cls.__name__ + '_popular_tags')
+
−        if tags is None:
+
−            tags = cls.get_tags_by_frequency(limit)
+
−            memcache.add(cls.__name__ + '_popular_tags', tags, 3600)
+
−        
+
−        return tags
+
−
+
−    @classmethod
+
−    def expire_cached_tags(cls):
+
−        from google.appengine.api import memcache
+
−        
+
−        memcache.delete(cls.__name__ + '_popular_tags')
+
−        memcache.delete(cls.__name__ + '_tags_by_name_asc')
+
−        memcache.delete(cls.__name__ + '_tags_by_name_desc')
+
−
+
−class Taggable:
+
−    """A mixin class that is used for making Google AppEngine Model classes taggable.
+
−        Usage:
+
−            class Post(db.Model, taggable.Taggable):
+
−                body = db.TextProperty(required = True)
+
−                title = db.StringProperty()
+
−                added = db.DateTimeProperty(auto_now_add=True)
+
−                edited = db.DateTimeProperty()
+
−            
+
−                def __init__(self, parent=None, key_name=None, app=None, **entity_values):
+
−                    db.Model.__init__(self, parent, key_name, app, **entity_values)
+
−                    taggable.Taggable.__init__(self)
+
−    """
+
−    
+
−    def __init__(self, tag_model = Tag):
+
−        self.__tags = None
+
−        self.__tag_model = tag_model
+
−        self.tag_separator = ","
+
−        """The string that is used to separate individual tags in a string
+
−        representation of a list of tags.  Used by tags_string() to join the tags
+
−        into a string representation and tags setter to split a string into
+
−        individual tags."""
+
−
+
−    def __get_tags(self):
+
−        "Get a List of Tag objects for all Tags that apply to this object."
+
−        if self.__tags is None or len(self.__tags) == 0:
+
−            self.__tags = self.__tag_model.get_tags_for_key(self.key())
+
−        return self.__tags
+
−
+
−    def __set_tags(self, tags):
+
−        import types
+
−        if type(tags) is types.UnicodeType:
+
−            # Convert unicode to a plain string
+
−            tags = str(tags)
+
−        if type(tags) is types.StringType:
+
−            # Tags is a string, split it on tag_seperator into a list
+
−            tags = string.split(tags, self.tag_separator)
+
−        if type(tags) is types.ListType:
+
−            self.__get_tags()
+
−            # Firstly, we will check to see if any tags have been removed.
+
−            # Iterate over a copy of __tags, as we may need to modify __tags
+
−            for each_tag in self.__tags[:]:
+
−                if each_tag not in tags:
+
−                    # A tag that was previously assigned to this entity is
+
−                    # missing in the list that is being assigned, so we
+
−                    # disassocaite this entity and the tag.
+
−                    each_tag.remove_tagged(self.key())
+
−                    self.__tags.remove(each_tag)
+
−            # Secondly, we will check to see if any tags have been added.
+
−            for each_tag in tags:
+
−                each_tag = string.strip(each_tag)
+
−                if len(each_tag) > 0 and each_tag not in self.__tags:
+
−                    # A tag that was not previously assigned to this entity
+
−                    # is present in the list that is being assigned, so we
+
−                    # associate this entity with the tag.
+
−                    tag = self.__tag_model.get_or_create(each_tag)
+
−                    tag.add_tagged(self.key())
+
−                    self.__tags.append(tag)
+
−        else:
+
−            raise Exception, "tags must be either a unicode, a string or a list"
+
−        
+
−    tags = property(__get_tags, __set_tags, None, None)
+
−    
+
−    def tags_string(self):
+
−        "Create a formatted string version of this entity's tags"
+
−        to_str = ""
+
−        for each_tag in self.tags:
+
−            to_str += each_tag.tag
+
−            if each_tag != self.tags[-1]:
+
−                to_str += self.tag_separator
+
−        return to_str
+
−