Question:
Django version 1.10
class Game(models.Model):
game_code = models.CharField(max_length=10)
home_team = models.ForeignKey(Team, related_name="home_set", default=2, blank=True, null=True)
away_team = models.ForeignKey(Team, related_name="away_set", default=2, blank=True, null=True)
class GameCoefficient(models.Model):
game = models.ForeignKey(Game, default=3)
win_type = models.CharField(choices=win_type, max_length=250, blank=True, null=True, default="")
value = models.FloatField(max_length=250, blank=True, null=True, default="")
class BaseView(View):
data = dict()
template = "index.html"
def get(self, request):
self.data['coefficents_and_game'] = GameCoefficient.objects.all().select_related('game')
return render_to_response(self.template, self.data)
When rendering, I get the GameCoefficient and ForeignKey GAME, while the template gets the GameCoefficient model and if I do
{% for item in coefficents_and_game %}
{{item.game}}
{% endfor %}
in this case, the game code (game_code) is repeated by the number of GameCoefficient and I need to display Game and GameCoefficient in ONE request. But according to the Game table associated with this table GameCoefficient.
{% for game in coefficents_and_game %}
{{game.game_code}}
{% for coefficient in game %}
{{coefficient.win_type}}
{{coefficient.value}}
{% endfor %}
{% endfor %}
By the fact that I read this, you can do one of these operators "select_related" "fetch_reverse_relations" "prefetch_related" well, I could not fully understand the difference between them in order to achieve the result and display an example query in reverse order.
Answer:
select_related must be used for the querset of the model in which the ForeingKey is ForeingKey , i.e. in connection with many to one, on the side of many. prefetch_related works the other way around, on the one side it pulls up all related objects, it can also be used for many-to-many relationships.
Team.objects.prefetch_related('home_set')
Game.objects.select_related('home_team')
Both of these methods can be used to capture the relationships of related models.
In your case, to capture all 3 tables, you can use the following queriset:
self.data['coefficents_and_game'] = GameCoefficient.objects.select_related('game__home_team', 'game__away_team')
This is how you can refer to them in the template:
{% for game in coefficents_and_game %}
{{ game.win_type }}
{{ game.value }}
{% for coefficient in game.game %}
{{ coefficient.game_code }}
# Можно добавить еще один внутренний цикл
# по ключам home_team и away_team
{% endfor %}
{% endfor %}