如何通过多对多关系获取 django 模型？

Question

我得到了Player 实例（一个团队）的列表，例如team = [player1, player2, player3]

我如何通过一个查询“get_or_create”包含这些且只有这三个玩家的Team？

这些是我的 django 模型：

class Player(models.Model):
    name = models.CharField(max_length=100)

class Team(models.Model):
    players = models.ManyToManyField(Player)

Answer 1

文档说get_or_create 是一个快捷方式：

try:
    obj = Person.objects.get(first_name='John', last_name='Lennon')
except Person.DoesNotExist:
    obj = Person(first_name='John', last_name='Lennon', birthday=date(1940, 10, 9))
    obj.save()

所以我会根据您的用例进行如下调整：

from django.db.models import Q, Count
import operator

players = [player1, player2, player3]

team = Team.objects
    .filter(reduce(
         operator.and_,
         [Q(players=player) for player in players]
    ))
    .annotate(count=Count('players'))
    .filter(count=len(players))

# Note that this ^ returns a QuerySet. With your posted model there
# might exist several teams with exactly the same players.  

if not team.exists():
    team = Team.objects.create()
    team.players.add(*players)

稍微复杂一点，但工作流程是一样的：

• 查询是否存在。
• 如果不存在，则创建。