英文:
Django Python : Manager isn't accessible via model instances
问题
我试图查询一个对象集合并使用对象的数量来进行循环，以呈现每个对象的参数。我使用一个二维数组来存储这些参数，以便它们可以与其对象相对应地呈现。我希望不仅提供一个解决方案，还提供一种更好的通用方法。附言：我是django的新手
这是来自views.py的代码：
def flashcard(response):form = Flashcard_verif(response.POST)if response.method == "POST" and form.is_valid():head = form.cleaned_data["header"]ques = form.cleaned_data["question"]ans = form.cleaned_data["answer"]flashcard_data = Flashcard(header=head, question=ques, answer=ans)# 这是错误发生的地方flashcard_obj = Flashcard(header=head, question=ques, answer=ans).objects.all()rawHeader, rawQuestion, rawAnswer = Flashcard(header=head, question=ques, answer=ans).flash_format()flashcard_data.save()if len(flashcard_lib) > 1:for i in range(0, len(flashcard_lib), 1):flashcard_lib.append([rawHeader, rawQuestion, rawAnswer])print(flashcard_lib)return render(response, "main/Flashcard.html", {"form": form,"Flashcard_lib": flashcard_lib,"flashcard": flashcard_obj})else:flashcard_lib.append([rawHeader, rawQuestion, rawAnswer])print(flashcard_lib)return render(response, "main/Flashcard.html", {"form": form,"header": rawHeader,"question": rawQuestion,"answer": rawAnswer})else:form = Flashcard_verif()return render(response, "main/Flashcard.html", {"form": form})
这是使用二维数组的模板：
<div class="flashcard-view" id="flash" style="visibility: hidden">{% if Flashcard_lib|length >= 2 %}{% for i in flashcard_obj %}<div class="flashcard">{{ i.0 }}{{ i.1 }}{{ i.2 }}</div>{% endfor %}{% else %}<div class="flashcard">{{ header }}{{ question }}{{ answer }}</div>{% endif %}</div>
当我运行服务器时，我注意到if语句执行了，但for循环没有执行。这有点是一个两全其美的问题，如何让它遍历列表。
英文:
I'm trying to query an object set and use the number of the amount of objects to do a for loop that will present parameters of each object. I'm using a 2D array to store the parameters so they can be presented respective to their object. I would like not just a solution but a better way in general of doing this .p.s. I'm new to django
This is the code from views.py
def flashcard(response):form = Flashcard_verif(response.POST)if response.method == "POST" and form.is_valid():head = form.cleaned_data["header"]ques = form.cleaned_data["question"]ans = form.cleaned_data["answer"]flashcard_data = Flashcard(header=head, question=ques, answer=ans)# this is where the error is occuringflashcard_obj = Flashcard(header=head, question=ques, answer=ans).objects.all()rawHeader, rawQuestion, rawAnswer = Flashcard(header=head, question=ques, answer=ans).flash_format()flashcard_data.save()if len(flashcard_lib) > 1:for i in range(0, len(flashcard_lib), 1):flashcard_lib.append([rawHeader, rawQuestion, rawAnswer])print(flashcard_lib)return render(response, "main/Flashcard.html", {"form":form,"Flashcard_lib":flashcard_lib,"flashcard":flashcard_obj})else:flashcard_lib.append([rawHeader, rawQuestion, rawAnswer])print(flashcard_lib)return render(response, "main/Flashcard.html", {"form":form,"header":rawHeader,"question":rawQuestion,"answer":rawAnswer})else:form = Flashcard_verif()return render(response, "main/Flashcard.html", {"form":form})
This is my template that utilises the 2d array:
<div class="flashcard-view" id="flash" style="visibility: hidden">{% if Flashcard_lib|length >= 2 %}{% for i in flashcard_obj %}<div class="flashcard">{{ i.0 }}{{ i.1 }}{{ i.2 }}</div>{% endfor %}{% else %}<div class="flashcard">{{ header }}{{ question }}{{ answer }}</div>{% endif %}</div>
When i run the server I notice that the if statement executes but the for loop does not. This is kind've a 2 in 1 problem, how do i get it to iterate through the list.
答案1
得分: 0
在以下代码行中：
flashcard_data = Flashcard(header=head, question=ques, answer=ans)
你创建了一个 Flashcard 模型的实例，但没有将其保存到数据库中，要这样做，你需要执行：
flashcard_data.save()
在以下代码行中发生了错误：
flashcard_obj = Flashcard(header=head, question=ques, answer=ans).objects.all()
因为你创建了另一个实例（与上面两行代码中的实例具有相同的数据），然后尝试使用它来获取对象管理器。在 Django 模型实例中，可以表示为：
- 单个对象（如你的情况）
- 作为查询集 - 特殊的类似列表的结构，可以为空或包含一个或多个实例。
如果你想获取数据库中的所有 Flashcard 记录，你需要执行：
Flashcard.objects.all()
其中 Flashcard 是你的模型，objects 是对象管理器，它将允许你指定你需要什么：
Flashcard.objects.all()- 返回包含所有实例的查询集Flashcard.objects.filter(...)- 返回包含经过筛选的记录的查询集Flashcard.objects.first()- 返回数据库中的第一个对象（而不是查询集！）
等等。
你不能从实例中调用对象管理器。
英文:
In line
flashcard_data = Flashcard(header=head, question=ques, answer=ans)
You created instance of model Flashcard, but you didnt saved it to db, to do so you need to do:
flashcard_data.save()
An error occured in line
flashcard_obj = Flashcard(header=head, question=ques, answer=ans).objects.all()
because you created another instance (with same data as instance 2 lines above) and then you try to get obj manager with it. In Django model instances can be represented as:
- single objects (as in your case)
- As querysets - special list-like structures, empty or containing one or several instances.
If you want to get all Flashcard records in db you need to do
Flashcard.objects.all()
Where Flashcard - is your model, objects - is object manager, that will let you to specify what do you need -
Flashcard.objects.all() - returns queryset with all instases
Flashcard.objects.filter(...) - - returns queryset with filtered records
Flashcard.objects.first() - returns first object (not queryset!) in db
etc..
You cant call obj manager from instance
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