django ModelForms - 我做对了吗？

Posted 2023-02-24

【中文标题】django ModelForms - 我做对了吗？

【英文标题】：django ModelForms - am I doing it right?

【发布时间】：2017-12-26 21:38:51

【问题描述】：

我有一个使用 6 字段或 8 字段答案的投票应用扩展程序。我已经非常简单地定义了这些 ModelForms。

class expert_judgement_three_form(ModelForm):
"""From Burgman "Trusting Judgements" 2016 p95. Values are probabilities """
class Meta:
    model = EJ_three_field
    exclude = ['question','user']

[表格似乎需要在模板中进行大量手动配置才能使它们进入估算：基本原理对]

为了预填充字段，我创建了模型的一个对象实例，然后将其传递给表单，然后从表单中取回它。 the docs 中的示例逐项遍历cleaned_data 字典 - 它似乎并没有减少样板代码。我注意到this reply 并且我已经看到this answer 并且可能会以这种方式工作。

我无法摆脱我误解或误读了应该如何使用表单，尤其是模型表单的关键特性的感觉，因为仍然有很多东西是可见的（这给我带来了麻烦）。

这个问题的一个好的答案是尽可能稀疏的模型、ModelForm 和 View 用于一个多字段表单，它总是预先填写用户之前对问题的回答。

【参考方案1】：

基本上，Form 和 ModelForm 是不同的。表单由您手动配置，ModelForm 将自动创建。

如果您创建了模型，您通常希望允许用户通过表单创建这些模型。 Django 无需复制所有字段名称并自己创建表单，而是为此提供了一个快捷方式，即 ModelForm：

使用 Modelform 创建的模型表单示例：

forms.py

class expert_judgement_three_form(ModelForm):
"""From Burgman "Trusting Judgements" 2016 p95. Values are probabilities """
     class Meta:
           model = EJ_three_field
           exclude = ['question','user']

此表单自动具有与创建它的 EJ_three_field 模型相同的所有字段类型。

views.py

def create(request):
    form = expert_judgement_three_form(request.POST)
    if request.method == 'POST':
        form = expert_judgement_three_form(request.POST)
        print form.errors
        if form.is_valid :
            print "all validation passed"
            # commit=False tells Django that "Don't send this to database yet.
            expert_judgement_three_form = form.save(commit=False)
            expert_judgement_three_form.save()
            return (request, "")
        else:
             print form.errors
    else:
        form = expert_judgement_three_form(request.POST)
    return render(request, "","form":form)

def edit(request,pk):
    EJ_three_field_object = EJ_three_field.objects.get(pk=pk)
    form = expert_judgement_three_form(request.POST,instance=EJ_three_field_object)
    if request.method == 'POST':
        form = expert_judgement_three_form(request.POST,instance=EJ_three_field_object)
        print form.errors
        if form.is_valid :
            print "all validation passed"
            # commit=False tells Django that "Don't send this to database yet.
            expert_judgement_three_form = form.save(commit=False)
            expert_judgement_three_form.save()
            return (request, "")
        else:
             print form.errors
    else:
        form = expert_judgement_three_form(request.POST,instance=EJ_three_field_object)enter code here
    return render(request, "","form":form)

urls.py

url(r'^create/', views.create, name='create'),
#edit
url(r'^edit/(?P<pk>\d+)/$',views.edit,name='edit'),

文档：Creating forms from ModelForm

【讨论】：

谢谢埃米尔。你能解释一下为什么推荐这种两态过程吗？ codeexpert_judgement_three_form = form.save(commit=False) Expert_judgement_three_form.save() code

你可以给任何变量而不是expert_judgement_three_form。它只是一个变量。commit=False 告诉 Django “不要将它发送到数据库。我还有更多事情要做它。”如果你愿意，你可以在这里设置用户对象。

【参考方案2】：

我会这样解释。

1

不使用form模板标签，你应该自己写<form action="." method="post">% csrf token % <label ...> <input type ...> .. </form>。因此，通过使用表单，您可以减少编写所有这些的时间。

2

如果没有 modelForm，您需要指定每个输入。

class Example(forms.Form):
    example1 = forms.CharField(label="label name", max_length=100)
    example2 = forms.IntergerField()
    ... what if you have 10 inputs?, you should write all 10 inputs

但是如果你已经定义了你的模型（在很多情况下，你会在你的数据库中保存或更新表单。这意味着你已经定义了你的模型。），你可以简单地使用 ModelForm 而无需花时间自己编写 FormField。

class Example(ModelForm):
    class Meta:
        Model : yourModel
        fields : ['example1', 'example2', ...]

我想我会很安全。如果你定义你的模型元素像

#model.py
class ExampleModelCalss(models.Model):
    example1 = models.CharField(max_length=50)

#forms.py
class ExampleFormClass(forms.Form):
    example1 = forms.CharField(max_length=100)

您可以输入长度为 70 的文本，因此它通过了表单验证，但是当它保存在您的数据库中时会发生什么？

所以我的想法是这样的。我很好奇其他人是怎么想的。

此外，您还可以混合使用。 例如，

#models.py
class ExampleModelCalss(models.Model):
    example1 = models.CharField(max_length=50)
    example2 = models.IntegerField(default=0)

你想添加一个不在你的模型中。

class ExampleMixForm(forms.ModelForm)
    example3 = forms.CharField(max_length=50) # adding
    
    class Meta:
        Model : ExampleModelCalss
        fields = ['example1', 'example2', 'example3'] # adding

【参考方案3】：

我现在可以工作了！我想我会提出这个工作代码，以防有人发现它有用。可能使这变得有趣的困难来源之一是，我仅将表单用于多字段答案，而不将它们用于单字段答案。任何对此的评论都将受到欢迎。我对此很陌生。

models.py

class Question(models.Model):
...
class Answer(models.Model):
    question = models.ForeignKey(Question, on_delete=models.CASCADE)
    user = models.ForeignKey(User, on_delete=models.CASCADE, default = 1)
    class Meta:
        abstract = True

# What follows is a class method that gets existing answers, creates new default entries or updates answers depending on when it is called. It assumes that each question is answered only once.
    @classmethod
    def get_or_update_answer(self, user, question, submitted_value=None):
        if question.answer_type == 'CH':
            if submitted_value == None:
                selected_choice = question.choice_set.first() # by default, select the top of a set of radio buttons
                answer, _created = Vote.objects.get_or_create(user = user, question = question, defaults='choice':selected_choice)

            else:
                selected_choice = question.choice_set.get(pk=submitted_value)
                answer = Vote.objects.get(user = user, question = question)
                answer.choice = selected_choice

        if question.answer_type == 'SA':
            if submitted_value == None:
                submitted_value = "brief response"
                answer, _created = Short_Answer.objects.get_or_create(user = user, question = question, defaults='short_answer': submitted_value)

            else:
                answer = Short_Answer.objects.get(user = user, question = question)
                answer.short_answer = submitted_value

        if question.answer_type == 'LA':
            if submitted_value == None:
                submitted_value = "full response"
                answer, _created = Long_Answer.objects.get_or_create(user = user, question = question, defaults='long_answer':submitted_value)

            else:
                answer = Long_Answer.objects.get(user = user, question = question)
                answer.long_answer = submitted_value
        if question.answer_type == 'E3':
            if submitted_value == None:
                submitted_value = 'lowest_value': 0, 'lv_rationale': "low estimate reasons",
                                  'highest_value':0,  'hv_rationale': "high estimate reasons",
                                  'best_value':0, 'bv_rationale': "best estimate reasons",
                answer, _created = EJ_three_field.objects.get_or_create(user= user, question = question, defaults=submitted_value)
            else:
                answer = EJ_three_field.objects.get(user= user, question = question)
                for key, value in submitted_value.items():
                    setattr(answer,key,value)
        if question.answer_type == 'E4':
            if submitted_value == None:
                submitted_value = 'lowest_value': 0, 'lv_rationale': "low estimate reasons",
                                  'highest_value':0,  'hv_rationale': "high estimate reasons",
                                  'best_value':0, 'bv_rationale': "best estimate reasons",
                                  'confidence': 0, 'conf_rationale': "reasons for confidence score",
                answer, _created = EJ_four_field.objects.get_or_create(user = user, question = question, defaults=submitted_value)
            else:
                answer = EJ_four_field.objects.get(user= user, question = question)
                for key, value in submitted_value.items():
                    setattr(answer,key,value)
        # answer.save() - not required for create / update funcs
        answer.save()
        return answer

class Short_Answer(Answer):
class Long_Answer(Answer):
class Vote(Answer):
class EJ_three_field(Answer):
class EJ_four_field(Answer):

Views.py

def pageView(request, user_id, page_num):
    question_set = Question.objects.filter(man_page = page_num)
    user = User.objects.get(username = user_id)
    template = 'polls/page_question.html'
    context = 'question_set' : question_set, 
    forms = 
    answers = 
    for question in question_set:
        answers[question] = Answer.get_or_update_answer(user, question)
        form_instance = form_instantiator(question, instance = answers[question])
        forms[question] = form_instance

    context['forms']=forms
    context['answers']=answers
    return render(request, template, context)

@login_required
def answer(request, user_id, man_index):
    #attempt to standardise saving of answers (votes, shorts, longs, E3, vE4 etc)
    user = User.objects.get(username = user_id)
    question = Question.objects.get(man_index = man_index)
    form_instance = form_instantiator(question, request = request)
    if form_instance == None:
        answer_value = request.POST['answer_value']
        Answer.get_or_update_answer(user = user, question = question, submitted_value = answer_value)
    else:
        form = form_instantiator(question, request = request)
        if form.is_valid():
            print(form.cleaned_data)
            Answer.get_or_update_answer(user = user, question = question, submitted_value = form.cleaned_data)
    return HttpResponseRedirect(reverse('polls:page', args=(user_id, question.man_page)))

回答我最初的问题：可以使用 (instance=) 或 (request.POST) 或未绑定创建 ModelForm，两者都不绑定。提交数据时，会丢弃与上下文一起传递的对象。一个ModelForm可以用form.save()保存，效率很高。