如何从Django模板访问多对多“直通”表的属性？

Question

从Django文档。。。

When you're only dealing with simple many-to-many relationships such as mixing and matching pizzas and toppings, a standard ManyToManyField is all you need. However, sometimes you may need to associate data with the relationship between two models.

For example, consider the case of an application tracking the musical groups which musicians belong to. There is a many-to-many relationship between a person and the groups of which they are a member, so you could use a ManyToManyField to represent this relationship. However, there is a lot of detail about the membership that you might want to collect, such as the date at which the person joined the group.

For these situations, Django allows you to specify the model that will be used to govern the many-to-many relationship. You can then put extra fields on the intermediate model. The intermediate model is associated with the ManyToManyField using the through argument to point to the model that will act as an intermediary. For our musician example, the code would look something like this:

class Person(models.Model):
    name = models.CharField(max_length=128)

    def __unicode__(self):
        return self.name

class Group(models.Model):
    name = models.CharField(max_length=128)
    members = models.ManyToManyField(Person, through='Membership')

    def __unicode__(self):
        return self.name

class Membership(models.Model):
    person = models.ForeignKey(Person)
    group = models.ForeignKey(Group)
    date_joined = models.DateField()
    invite_reason = models.CharField(max_length=64)

Now that you have set up your ManyToManyField to use your intermediary model (Membership, in this case), you're ready to start creating some many-to-many relationships. You do this by creating instances of the intermediate model:

ringo = Person.objects.create(name="Ringo Starr")
paul = Person.objects.create(name="Paul McCartney")
beatles = Group.objects.create(name="The Beatles")

m1 = Membership(person=ringo, group=beatles,
...     date_joined=date(1962, 8, 16),
...     invite_reason= "Needed a new drummer.")

m1.save()

beatles.members.all()
[<Person: Ringo Starr>]

ringo.group_set.all()
[<Group: The Beatles>]

m2 = Membership.objects.create(person=paul, group=beatles,
...     date_joined=date(1960, 8, 1),
...     invite_reason= "Wanted to form a band.")

beatles.members.all()
[<Person: Ringo Starr>, <Person: Paul McCartney>]

source: http://docs.djangoproject.com/en/dev/topics/db/models/#intermediary-manytomany

我的问题是，如何设置视图和模板来访问这些附加属性。假设我有一个带区页面，我想显示带区名称，遍历成员记录，显示名称和加入日期。

我应该将band对象传递给模板吗？或者我是否以某种方式传递成员对象？

如何在模板中创建for循环？

谢谢。

Answer 1

我不确定这是否是唯一的解决方案，但将关系对象传递给模板肯定有效。在您的视图中，获取成员对象的QuerySet：

rel = Membership.objects.filter( group = your_group ).select_related()

并将其传递给模板，在模板中可以使用{% for %}对其进行迭代

{% for r in rel %}
     {{ r.person.name }} joined group {{ r.group.name }} on {{ r.date_joined }}<br />
{% endfor %}

注意，由于select_related()，这不应该执行任何其他查询。

Answer 2

最简单的方法就是将波段传递给模板。模板能够导航模型之间的关系，并且组上同时有成员和成员集查询集管理器。所以我要这样做：

视图：

def group_details(request, group_id):
    group = get_object_or_404(Group, pk=group_id)
    return render_to_response('group_details.html',
                              {'group': group})

模板：

<h2>{{ group.name }}</h2>
{% for membership in group.membership_set.all %}
    <h3>{{ membership.person }}</h3>
    {{ membership.date_joined }}
{% endfor %}