Django查询集索引

我想知道在模型上使用索引是否可行:

class Buildings(models.Model):
    island = models.ForeignKey(Island)
    townhall = models.IntegerField(default=1)
    lumberjack = models.IntegerField(default=0)
    stonequarry = models.IntegerField(default=0)
    ironmine = models.IntegerField(default=0)
    [...]

a=Buildings.objects.get(somecondition)
print a.townhall # 1
a[1] +=1
print a.townhall # 2

目前它抛出

“typeerror:'建筑物'对象是 不可索引的

我之所以要这样做,是因为使用索引可以简化以下代码部分:

if queue.kind_id == 0: buildings.townhall += 1
elif queue.kind_id == 1: buildings.lumberjack += 1
elif queue.kind_id == 2: buildings.stonequarry += 1
elif queue.kind_id == 3: buildings.ironmine += 1
elif queue.kind_id == 4: buildings.factory += 1
elif queue.kind_id == 5: buildings.shipyard += 1
elif queue.kind_id == 6: buildings.university += 1

对此:

buildings[queue.kind_id] +=1