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django - 如何加入这些 Django 模型？

问题描述

我应该如何加入这些 Django 模型以获取所有参与登录用户挑战的 Player 模型（请参阅 views.py 中名为 challenge_participants 的变量？我没有想出如何使用 Django 模型有效实现这一点的解决方案。谢谢很多！

示例数据：假设 John 已登录。正如我们在 PlayerChallenge 模型中看到的那样，他是挑战 1 和 2 的一部分。我要做的是获取属于挑战 1 的所有玩家对象（Roger 就是这个例子）以及属于挑战 2 一部分的所有玩家对象的第二个列表（本例中为 Roger 和 Claude）。

播放器型号

╔═══════════╦═════════╦════════════════╗
║ user_name ║ user_id ║ wallet_balance ║
╠═══════════╬═════════╬════════════════╣
║ John      ║     123 ║             20 ║
║ Roger     ║     231 ║             15 ║
║ Claude    ║     582 ║             10 ║
╚═══════════╩═════════╩════════════════╝

挑战模式

╔════╦═════════╦══════╦════════╦═══════════════════╦══════════╦═══════════════════╦═══════════════╗
║ id ║ status  ║ type ║ amount ║ created_timestamp ║ duration ║ started_timestamp ║ end_timestamp ║
╠════╬═════════╬══════╬════════╬═══════════════════╬══════════╬═══════════════════╬═══════════════╣
║  1 ║ active  ║    1 ║     20 ║ TimeStamp         ║ 02:00:00 ║ TimeStamp         ║ TimeStamp     ║
║  2 ║ waiting ║    2 ║     30 ║ TimeStamp         ║ 04:00:00 ║ TimeStamp         ║ TimeStamp     ║
║  3 ║ waiting ║    1 ║     35 ║ TimeStamp         ║ 07:00:00 ║ TimeStamp         ║ TimeStamp     ║
╚════╩═════════╩══════╩════════╩═══════════════════╩══════════╩═══════════════════╩═══════════════╝

玩家挑战模型

╔════╦════════╦═══════════╦════════════════════╗
║ id ║ player ║ challenge ║ accepted_timestamp ║
╠════╬════════╬═══════════╬════════════════════╣
║  1 ║ John   ║         1 ║ TimeStamp          ║
║  2 ║ Roger  ║         1 ║ TimeStamp          ║
║  3 ║ Roger  ║         2 ║ TimeStamp          ║
║  4 ║ Claude ║         2 ║ TimeStamp          ║
║  5 ║ John   ║         2 ║ TimeStamp          ║
╚════╩════════╩═══════════╩════════════════════╝

代码：

模型.py

from django.db import models
from django.contrib.auth.models import User
from django.db.models.signals import post_save
from django.dispatch import receiver

# Create your models here.

class Player(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    #additional fields
    userid = models.CharField(max_length=256)
    wallet_balance = models.IntegerField(default=0)
    def __str__(self):
        return self.user.username

@receiver(post_save, sender=User)
def create_user_profile(sender, instance, created, **kwargs):
    if created:
        Player.objects.create(user=instance)

@receiver(post_save, sender=User)
def save_user_profile(sender, instance, **kwargs):
    instance.player.save()


class Challenge(models.Model):
    id = models.IntegerField(primary_key=True, unique=True)
    status = models.CharField(max_length=20)
    type = models.CharField(max_length=20)
    amount = models.DecimalField(max_digits=10, decimal_places=2)
    created_timestamp = models.DateTimeField()
    duration = models.DurationField()
    started_timestamp = models.DateTimeField(null=True, blank=True)
    end_timestamp = models.DateTimeField(null=True, blank=True)

    def __str__(self):
        return str(self.id)

class PlayerChallenge(models.Model):
    user_challenge_id = models.IntegerField(primary_key=True, unique=True)
    player = models.ForeignKey(Player, on_delete=models.CASCADE)
    challenge = models.ForeignKey(Challenge, on_delete=models.CASCADE)
    accepted_timestamp = models.DateTimeField(null=True, blank=True)

    def __str__(self):
        return str(self.user_challenge_id) + " (Player: " + str(self.player.user.username) + ", Challenge: " + str(self.challenge.id) + ")"

视图.py

from django.shortcuts import render
from django.http import HttpResponse

from django.contrib.auth import authenticate, login, logout
from django.http import HttpResponseRedirect, HttpResponse
from django.urls import reverse
from django.contrib.auth.decorators import login_required
from django.contrib.auth.models import User

from challengeview.models import Player,Challenge,PlayerChallenge

@login_required
def index(request):

    challenges = Challenge.objects.filter(playerchallenge__player = request.user.player)
    challenges_participants = Player.objects.filter(playerchallenge__challenge = challenges)

    my_dict = {
     'challenges_participants' : challenges_participants,
     'challenges' : challenges,

    }
    return render(request, "challengeview/index.html", context=my_dict)

多谢您的支持！

标签： djangodjango-models

解决方案

在 Django 中，您不能像在简单的SQL表中那样对关系进行建模。有 3 种强大的关系类型OnetoOne, ForeignKey, ManytoMany。从 django.utils 导入时区

class Player(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    #additional fields
    userid = models.CharField(max_length=256)
    wallet_balance = models.IntegerField(default=0)
    challenges = models.ManyToMany('Challenge') #a challenge can be belonged to many players in this case
    def __str__(self):
        return self.user.username

@receiver(post_save, sender=User)
def create_user_profile(sender, instance, created, **kwargs):
    if created:
        Player.objects.create(user=instance)

@receiver(post_save, sender=User)
def save_user_profile(sender, instance, **kwargs):
    instance.player.save()


class Challenge(models.Model):
    status = models.CharField(max_length=20)
    type = models.CharField(max_length=20)
    amount = models.DecimalField(max_digits=10, decimal_places=2)
    duration = models.DurationField()
    started_timestamp = models.DateTimeField(null=True, blank=True)
    end_timestamp = models.DateTimeField(null=True, blank=True)
    created_timestamp = models.DateTimeField()

    def __str__(self):
        return str(self.id)


class PlayerActivity(models.Model):
    challenge = models.ForeingKey(on_delete=models.SET_NULL,
                                   null=True,
                                 related_name='activity_challenge')
    created_by = models.ForeignKey(Player,
                                   on_delete=models.SET_NULL,
                                   null=True,
                                 related_name='activity_created_by')

    created_at = models.DateTimeField(default=timezone.now)

    def __str__(self):
        return str(self.user_challenge_id) + " (Player: " + str(self.player.user.username) + ", Challenge: " + str(self.challenge.id) + ")"

如果一个挑战只能属于一个玩家，但一个玩家可以有很多挑战，那么Foreignkey。如果一个玩家可以有很多挑战并且一个挑战可以属于许多玩家，那么 ManyToMany。

当您使用查询时，您应该始终考虑发送到后端的请求。您可以使用select_related最小化请求。 

all_challenges = Challenge.objects.all()
logged_user_challenges = Player.objects.filter(user=request.user,challenges__in=all_challenges)
others_same_challenges = Player.objects.filter(challenges=logged_user_challenges.challenges)

或者

logged_user_challenges = PlayerActivity.objects.filter(user=request.user).latest('created_at')

但是你会遇到其他人的问题......你需要一个循环来获取所有内容，这只是不建议。

注意：您必须在视图中操作数据节省。

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