How to access a dictionary element in a Django template?
PythonDjangoDjango TemplatesPython Problem Overview
I would like to print out the number of votes that each choice got. I have this code in a template:
{% for choice in choices %}
{{choice.choice}} - {{votes[choice.id]}} <br />
{% endfor %}
votes
is just a dictionary while choices
is a model object.
It raises an exception with this message:
"Could not parse the remainder"
Python Solutions
Solution 1 - Python
choices = {'key1':'val1', 'key2':'val2'}
Here's the template:
<ul>
{% for key, value in choices.items %}
<li>{{key}} - {{value}}</li>
{% endfor %}
</ul>
Basically, .items
is a Django keyword that splits a dictionary into a list of (key, value)
pairs, much like the Python method .items()
. This enables iteration over a dictionary in a Django template.
Solution 2 - Python
you can use the dot notation:
> Dot lookups can be summarized like > this: when the template system > encounters a dot in a variable name, > it tries the following lookups, in > this order: > > - Dictionary lookup (e.g., foo["bar"]) > - Attribute lookup (e.g., foo.bar) > - Method call (e.g., foo.bar()) > - List-index lookup (e.g., foo[2]) > > The system uses the first lookup type > that works. It’s short-circuit logic.
Solution 3 - Python
To echo / extend upon Jeff's comment, what I think you should aim for is simply a property in your Choice class that calculates the number of votes associated with that object:
class Choice(models.Model):
text = models.CharField(max_length=200)
def calculateVotes(self):
return Vote.objects.filter(choice=self).count()
votes = property(calculateVotes)
And then in your template, you can do:
{% for choice in choices %}
{{choice.choice}} - {{choice.votes}} <br />
{% endfor %}
The template tag, is IMHO a bit overkill for this solution, but it's not a terrible solution either. The goal of templates in Django is to insulate you from code in your templates and vice-versa.
I'd try the above method and see what SQL the ORM generates as I'm not sure off the top of my head if it will pre-cache the properties and just create a subselect for the property or if it will iteratively / on-demand run the query to calculate vote count. But if it generates atrocious queries, you could always populate the property in your view with data you've collected yourself.
Solution 4 - Python
You need to find (or define) a 'get' template tag, for example, here.
The tag definition:
@register.filter
def hash(h, key):
return h[key]
And it’s used like:
{% for o in objects %}
<li>{{ dictionary|hash:o.id }}</li>
{% endfor %}
Solution 5 - Python
Similar to the answer by @russian_spy :
<ul>
{% for choice in choices.items %}
<li>{{choice.0}} - {{choice.1}}</li>
{% endfor %}
</ul>
This might be suitable for breaking down more complex dictionaries.
Solution 6 - Python
django_template_filter filter name get_value_from_dict
{{ your_dict|get_value_from_dict:your_key }}
Solution 7 - Python
Ideally, you would create a method on the choice object that found itself in votes, or create a relationship between the models. A template tag that performed the dictionary lookup would work, too.
Solution 8 - Python
Could find nothing simpler and better than this solution. Also see the doc.
@register.filter
def dictitem(dictionary, key):
return dictionary.get(key)
But there's a problem (also discussed here) that the returned item is an object and I need to reference a field of this object. Expressions like {{ (schema_dict|dictitem:schema_code).name }}
are not supported, so the only solution I found was:
{% with schema=schema_dict|dictitem:schema_code %}
<p>Selected schema: {{ schema.name }}</p>
{% endwith %}
UPDATE:
@register.filter
def member(obj, name):
return getattr(obj, name, None)
So no need for a with
tag:
{{ schema_dict|dictitem:schema_code|member:'name' }}
Solution 9 - Python
You could use a namedtuple instead of a dict. This is a shorthand for using a data class. Instead of
person = {'name': 'John', 'age': 14}
...do:
from collections import namedtuple
Person = namedtuple('person', ['name', 'age'])
p = Person(name='John', age=14)
p.name # 'John'
This is the same as writing a class that just holds data. In general I would avoid using dicts in django templates because they are awkward.