Django ManyToMany认证不起作用

Question

I'm trying to do this in my models.py:

class Tag(models.Model):
    ''' snip '''
    name = models.CharField(max_length=30)

class Stuff(models.Model):
    kind = models.CharField(max_length=30)
    tag = models.ManyToManyField(Tag)

But when I make query from Stuff in shell the relationship fields return 'None' like this:

>>> q = Stuff.objects.all()
>>> p = q.tag.name
>>> print q.tag.name
None

I can't use this keys in my template too.

Database backend is mysql.

What is the problem?

Answer 1

You can call many to many relation like this,

q = Stuff.objects.all()
for p in q.tag.all():
   print p.name

In HTML

{%for tag in stuff.tag.all %}
{{ tag.name }}
{% endfor %}

Answer 2

It's unclear how exactly you want your models to work. Do you want Stuff to have a single Tag or several Tags?

Solutions for both case uses follow.

The case where a Stuff object has many Tags

There are some mistakes here.

1. In your example the variable q isn't a Stuff object, so you can't ask for it's attributes. It's a queryset . Like the other answer exemplifies you have to iterate through it, like a list.
2. A ManyToMany relationship means that Stuff is going to have many Tags, but you're using it as if Stuff had only one Tag.

An example (I'm going to replace Stuff.tag by Stuff.tags , since it's misleading to call it a single tag):

# Get the first stuff
>>> stuff = Stuff.objects.first()
# Access the attribute `tag`. Notice it's NOT a Tag, but a `RelatedManager`.
>>> stuff.tag
<django.db.models.fields.related.ManyRelatedManager object at 0x7fe2a3e5cc10>
# which you can use as a queryset!!
>>> stuff.tag.all()
[<Tag: tag1>, <Tag: tag2>, ...]
# Then you can iterate through it, filter or whatever
>>> stuff.tag[0]
<Tag: tag1>
>>> stuff.tag[0].name
u'tag1'

The case where a Stuff object has a single Tag

If you want Stuff to have only ONE Tag object you have to declare it like this.

tag = models.OneToOneField(Tag)

NOW you can do stuff.tag.name and use it like that in the template. If you want many Tags you'll have to iterate through the Stuff's Tags like this (again, I'm using tags instead of tag for this example):

{% for tag in stuff.tags %}
    {{ tag.name }}
{% endfor %}

There are of course other ways, like using the filter join

{# Print the tag names joined by ', ' #}
{{ stuff.tags.all|join:', ' }}