python - 将原始 sql 映射到 django orm

Question

有没有办法简化这个工作代码？此代码获取一个对象的所有不同投票类型，大约有 20 种可能，并对每种类型进行计数。我不喜欢编写原始 sql，而是使用 orm。这有点棘手，因为我在模型中使用通用外键。

def get_object_votes(self, obj):
    """ 
    Get a dictionary mapping vote to votecount
    """
    ctype = ContentType.objects.get_for_model(obj)

    cursor = connection.cursor()
    cursor.execute("""
       SELECT v.vote , COUNT(*)
       FROM votes v
       WHERE %d = v.object_id AND %d = v.content_type_id
       GROUP BY 1
       ORDER BY 1 """ % ( obj.id, ctype.id )
    )
    votes = {}

    for row in cursor.fetchall():
       votes[row[0]] = row[1]

    return votes

我使用的模型

class Vote(models.Model):
    user = models.ForeignKey(User)

    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    payload = generic.GenericForeignKey('content_type', 'object_id')

    vote = models.IntegerField(choices = possible_votes.items() )


class Issue(models.Model):
    title = models.CharField( blank=True, max_length=200)

Answer 1

下面的代码对我有用!

def get_object_votes(self, obj, all=False):
    """
    Get a dictionary mapping vote to votecount
    """
    object_id = obj._get_pk_val()
    ctype = ContentType.objects.get_for_model(obj)
    queryset = self.filter(content_type=ctype, object_id=object_id)

    if not all:
        queryset = queryset.filter(is_archived=False) # only pick active votes

    queryset = queryset.values('vote')
    queryset = queryset.annotate(vcount=Count("vote")).order_by()

    votes = {}

    for count in queryset:
        votes[count['vote']] = count['vcount']

    return votes