How to access a dictionary element in a Django template?
Question:
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"
Answers:
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 %}
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.
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.
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.
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.
django_template_filter
filter name get_value_from_dict
{{ your_dict|get_value_from_dict:your_key }}
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.
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' }}
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.
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"
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 %}
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.
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.
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.
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.
django_template_filter
filter name get_value_from_dict
{{ your_dict|get_value_from_dict:your_key }}
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.
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' }}
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.