Question

Model.py：

class Match(models.Model):
    home_team = models.CharField(max_length=200)
    away_team = models.CharField(max_length=200)
class Stat(models.Model):
    match = models.ForeignKey(Match)
    team = models.CharField(max_length=100)
    goals = models.IntegerField(default=0)
    assists = models.IntegerField(default=0)

views.py

context_dict = {}
match = Match.objects.get(pk=1)
home_stat = Stat.objects.get(match=match, team=match.home_team)
away_stat = Stat.objects.get(match=match, team=match.away_team)

context_dict['home_stat'] = home_stat
context_dict['away_stat'] = away_stat

return render(request, 'index.html', context_dict)

模板

goals: {{ home_stat.goals }} : {{ away_stat.goals }}
assists: {{ home_stat.assists }} : {{ away_stat.assists }}

django-debug-toolbar显示两个重复的查询： https://sfault-image.b0.upaiyun.com/220/984/2209840587-5a3e5ccccec87_articlex

SELECT "myapp_stat"."id", "myapp_stat"."match_id", "myapp_stat"."team", "myapp_stat"."goals", "myapp_stat"."assists" FROM "myapp_stat" WHERE ("myapp_stat"."match_id" = '1' AND "myapp_stat"."team" = '''TeamA''')
  Duplicated 2 times. 
F:\myproject\myapp/views.py in index(11)
  home_stat = Stat.objects.get(match=match, team=match.home_team)

SELECT "myapp_stat"."id", "myapp_stat"."match_id", "myapp_stat"."team", "myapp_stat"."goals", "myapp_stat"."assists" FROM "myapp_stat" WHERE ("myapp_stat"."match_id" = '1' AND "myapp_stat"."team" = '''TeamB''')
  Duplicated 2 times. 

F:\myproject\myapp/views.py in index(12)
away_stat = Stat.objects.get(match=match, team=match.away_team)

如何解决这个问题？

Answer 1

执行ORM查询时，您可以使用双下划线查找相关模型上的字段。试试这个：

home_stat = Stat.objects.get(match=match)
away_stat = Stat.objects.get(match=match)

Answer 2

正如您在ForeignKey到Stat中Match一样，您可以使用Django默认提供的相关名称stat_set来简化查询。
```
match.stat_set.filter(...)
```
您可以按team__in查找过滤统计信息。这意味着您需要一个SQL查询来获取这两个统计信息。
```
both_stats = match.stat_set.filter(team__in=[match.home_team, match.away_team])     
```

剩下的就是将它们作为单独的对象。

for stat in both_stats:
    if stat.team == match.home_team:
        context_dict['home_stat'] = stat
    elif stat.team == match.away_team:
        context_dict['away_stat'] = stat

总的来说，这会将sql查询的数量从2减少到1但会增加python工作。

Django SQL查询重复2次

2 个答案: