Django ModelForm for Many-to-Many字段

Question

考虑以下模型和形式：

class Pizza(models.Model):
    name = models.CharField(max_length=50)

class Topping(models.Model):
    name = models.CharField(max_length=50)
    ison = models.ManyToManyField(Pizza, blank=True)

class ToppingForm(forms.ModelForm):
    class Meta:
        model = Topping

当你查看ToppingForm时，它可以让你选择浇头上的披萨，一切都只是花花公子。

我的问题是：如何定义一个ModelForm for Pizza，让我可以利用Pizza和Topping之间的多对多关系，让我选择Toppings在披萨上的内容？

Answer 1

我想你可以在这里向你的ModelMultipleChoiceField添加一个新的PizzaForm，并手动将该表单字段与模型字段链接，因为Django不会自动为你做这个。

以下代码段可能会有所帮助：

class PizzaForm(forms.ModelForm):
    class Meta:
        model = Pizza

    # Representing the many to many related field in Pizza
    toppings = forms.ModelMultipleChoiceField(queryset=Topping.objects.all())

    # Overriding __init__ here allows us to provide initial
    # data for 'toppings' field
    def __init__(self, *args, **kwargs):
        # Only in case we build the form from an instance
        # (otherwise, 'toppings' list should be empty)
        if kwargs.get('instance'):
            # We get the 'initial' keyword argument or initialize it
            # as a dict if it didn't exist.                
            initial = kwargs.setdefault('initial', {})
            # The widget for a ModelMultipleChoiceField expects
            # a list of primary key for the selected data.
            initial['toppings'] = [t.pk for t in kwargs['instance'].topping_set.all()]

        forms.ModelForm.__init__(self, *args, **kwargs)

    # Overriding save allows us to process the value of 'toppings' field    
    def save(self, commit=True):
        # Get the unsave Pizza instance
        instance = forms.ModelForm.save(self, False)

        # Prepare a 'save_m2m' method for the form,
        old_save_m2m = self.save_m2m
        def save_m2m():
           old_save_m2m()
           # This is where we actually link the pizza with toppings
           instance.topping_set.clear()
           instance.topping_set.add(*self.cleaned_data['toppings'])
        self.save_m2m = save_m2m

        # Do we need to save all changes now?
        if commit:
            instance.save()
            self.save_m2m()

        return instance

然后可以在任何地方使用此PizzaForm，即使在管理员中也是如此：

# yourapp/admin.py
from django.contrib.admin import site, ModelAdmin
from yourapp.models import Pizza
from yourapp.forms import PizzaForm

class PizzaAdmin(ModelAdmin):
  form = PizzaForm

site.register(Pizza, PizzaAdmin)

注意

save()方法可能有点过于冗长，但如果您不需要支持commit=False情况，则可以简化它，那就是：

def save(self):
  instance = forms.ModelForm.save(self)
  instance.topping_set.clear()
  instance.topping_set.add(*self.cleaned_data['toppings'])
  return instance

Answer 2

我不确定我是100％得到这个问题，所以我将按照这个假设运行：

每个Pizza可以包含多个Topping个。每个Topping都可以包含多个Pizza个。但是，如果将Topping添加到Pizza，则Topping会自动生成Pizza，反之亦然。

在这种情况下，最好的选择是关系表，Django支持得很好。它看起来像这样：

<强> models.py

class PizzaTopping(models.Model):
    topping = models.ForeignKey('Topping')
    pizza = models.ForeignKey('Pizza')
class Pizza(models.Model):     
    name = models.CharField(max_length=50) 
    topped_by = models.ManyToManyField('Topping', through=PizzaTopping)
    def __str__(self):
        return self.name
    def __unicode__(self):
        return self.name
class Topping(models.Model):   
    name=models.CharField(max_length=50)
    is_on = models.ManyToManyField('Pizza', through=PizzaTopping)
    def __str__(self):
        return self.name
    def __unicode__(self):
        return self.name

<强> forms.py

class PizzaForm(forms.ModelForm):
    class Meta:
        model = Pizza
class ToppingForm(forms.ModelForm):
    class Meta:
        model = Topping

示例：

>>> p1 = Pizza(name="Monday")
>>> p1.save()
>>> p2 = Pizza(name="Tuesday")
>>> p2.save()
>>> t1 = Topping(name="Pepperoni")
>>> t1.save()
>>> t2 = Topping(name="Bacon")
>>> t2.save()
>>> PizzaTopping(pizza=p1, topping=t1).save() # Monday + Pepperoni
>>> PizzaTopping(pizza=p2, topping=t1).save() # Tuesday + Pepperoni
>>> PizzaTopping(pizza=p2, topping=t2).save() # Tuesday + Bacon

>>> tform = ToppingForm(instance=t2) # Bacon
>>> tform.as_table() # Should be on only Tuesday.
u'<tr><th><label for="id_name">Name:</label></th><td><input id="id_name" type="text" name="name" value="Bacon" maxlength="50" /></td></tr>\n<tr><th><label for="id_is_on">Is on:</label></th><td><select multiple="multiple" name="is_on" id="id_is_on">\n<option value="1">Monday</option>\n<option value="2" selected="selected">Tuesday</option>\n</select><br /> Hold down "Control", or "Command" on a Mac, to select more than one.</td></tr>'

>>> pform = PizzaForm(instance=p1) # Monday
>>> pform.as_table() # Should have only Pepperoni
u'<tr><th><label for="id_name">Name:</label></th><td><input id="id_name" type="text" name="name" value="Monday" maxlength="50" /></td></tr>\n<tr><th><label for="id_topped_by">Topped by:</label></th><td><select multiple="multiple" name="topped_by" id="id_topped_by">\n<option value="1" selected="selected">Pepperoni</option>\n<option value="2">Bacon</option>\n</select><br /> Hold down "Control", or "Command" on a Mac, to select more than one.</td></tr>'

>>> pform2 = PizzaForm(instance=p2) # Tuesday
>>> pform2.as_table() # Both Pepperoni and Bacon
u'<tr><th><label for="id_name">Name:</label></th><td><input id="id_name" type="text" name="name" value="Tuesday" maxlength="50" /></td></tr>\n<tr><th><label for="id_topped_by">Topped by:</label></th><td><select multiple="multiple" name="topped_by" id="id_topped_by">\n<option value="1" selected="selected">Pepperoni</option>\n<option value="2" selected="selected">Bacon</option>\n</select><br /> Hold down "Control", or "Command" on a Mac, to select more than one.</td></tr>'

Answer 3

说实话，我会将多对多关系放入Pizza模型中。我认为这更贴近现实。想象一下，一个人订了几个比萨饼。他不会说“我想在比萨饼1和饼干上吃奶酪，在比萨饼1和饼干上吃西红柿”，但可能是“一个披萨配奶酪，一个披萨配奶酪和西红柿，......”。

当然可以让表格以你的方式运作，但我会选择：

class Pizza(models.Model):
    name = models.CharField(max_length=50)
    toppings = models.ManyToManyField(Topping)

Answer 4

另一种实现此目的的简单方法是创建一个中间表并使用内联字段来完成它。请参阅此https://docs.djangoproject.com/en/1.2/ref/contrib/admin/#working-with-many-to-many-intermediary-models

下面的一些示例代码

<强> models.py

class Pizza(models.Model):
    name = models.CharField(max_length=50)

class Topping(models.Model):
    name = models.CharField(max_length=50)
    ison = models.ManyToManyField(Pizza, through='PizzaTopping')

class PizzaTopping(models.Model):
    pizza = models.ForeignKey(Pizza)
    topping = models.ForeignKey(Topping)

<强> admin.py

class PizzaToppingInline(admin.TabularInline):
    model = PizzaTopping

class PizzaAdmin(admin.ModelAdmin):
    inlines = [PizzaToppingInline,]

class ToppingAdmin(admin.ModelAdmin):
    inlines = [PizzaToppingInline,]

admin.site.register(Pizza, PizzaAdmin)
admin.site.register(Topping, ToppingAdmin)

Answer 5

我不确定这是否是你想要的，但你知道Pizza有topping_set属性吗？使用该属性，您可以轻松地在ModelForm中添加新的顶部。

new_pizza.topping_set.add(new_topping)

Answer 6

我们在使用django admin的应用中遇到了类似的问题。用户和组之间存在多对多的关系，并且无法轻松地将用户添加到组中。我为django创建了一个patch，这样做，但没有太多关注它;-)你可以阅读它并尝试将类似的解决方案应用到你的披萨/打顶问题。这种方式在浇头中，您可以轻松添加相关的比萨饼，反之亦然。

Answer 7

我使用用户管理表格在Clément代码中做了类似的事情：

# models.py
class Clinica(models.Model):
  ...
  users = models.ManyToManyField(User, null=True, blank=True, related_name='clinicas')

# admin.py
class CustomUserChangeForm(UserChangeForm):
  clinicas = forms.ModelMultipleChoiceField(queryset=Clinica.objects.all())

  def __init__(self,*args,**kwargs):
    if 'instance' in kwargs:
      initial = kwargs.setdefault('initial',{})
      initial['clinicas'] = kwargs['instance'].clinicas.values_list('pk',flat=True)
    super(CustomUserChangeForm,self).__init__(*args,**kwargs)

  def save(self,*args,**kwargs):
    instance = super(CustomUserChangeForm,self).save(*args,**kwargs)
    instance.clinicas = self.cleaned_data['clinicas']
    return instance

  class Meta:
    model = User

admin.site.unregister(User)

UserAdmin.fieldsets += ( (u'Clinicas', {'fields': ('clinicas',)}), )
UserAdmin.form = CustomUserChangeForm

admin.site.register(User,UserAdmin)

Answer 8

如果要添加依赖于关系中表的两个主键的内容，也可以使用穿透表。多对多关系使用称为桥接表的东西来存储依赖于主键的两个部分的内容。

例如，考虑模型中订单和产品之间的以下关系。py

class Order(models.Model):
    date = models.DateField()
    status = models.CharField(max_length=30)

class Product(models.Model):
    name = models.CharField(max_length=50)
    desc = models.CharField(max_length=50)
    price = models.DecimalField(max_dights=7,decimal_places=2)
    qtyOnHand = models.Integer()
    orderLine = models.ManyToManyField(Order, through='OrderLine')

class OrderLine(models.Model):
    product = models.ForeignKey(Product)
    order = models.ForeignKey(Order)
    qtyOrd = models.Integer()

在您的情况下，您将要做的是将ManyToMany放在浇头上，因为它使用户可以选择想要的披萨上的浇头。简单但功能强大的解决方案。