I'm displaying the number of search results, however, i do more than one search.
So to display the number of results i'd have to add them up.
So i've tried this:
<p>Found {{ products|length + categories|length + companies|length }} results.</p>
But i get an error.
How do i do this?
Django templates do not support arithmetic operators. However you can use the add filter. I think you need something like this:
<p>Found {{ products|length|add:categories|length|add:companies|length }} results.</p>
Alternatively you should calculate the total in the view and pass it pre-calculated to the template.
EDIT: Further to the comments, this version should work:
{% with categories|length as catlen %}
{% with companies|length as complen %}
<p>Found {{ products|length|add:catlen|add:complen }} results.</p>
{% endwith %}
{% endwith %}
However, this feels very hacky and it would be preferable to calculate the figure in the view.
I would do this in your view when you are creating your context dictionary:
'result_count': len(products) + len(categories) + len(companies)
Then, in your template, just use:
<p>Found {{ result_count }} results.</p>
I'd like to point that Van Gale's answer is not optimal.
From the QuerySet API documentation, you should use query.count() rather than len(query)
A count() call performs a SELECT COUNT(*) behind the scenes, so you
should always use count() rather than loading all of the record into
Python objects and calling len() on the result (unless you need to
load the objects into memory anyway, in which case len() will be
faster).
So the answer should be:
In the view:
'result_count': products.count() + categories.count() + companies.count()
The template remains unchanged
Related
I have a template that receives a list context variable, tags_list. I need to iterate over this list 'inserting' the tags in the template something like this:
{% for tag in tags_list %}
{{ tag.tag }}
{% endfor %}
When this renders it returns the text value of tag.tag, "{% tagxxx %}", not the rendered tag.
How can I cause the template render to render the value of a context variable? Alternately, is there a filter, a sort of inverse verbatim, that will cause the value of a context variable to be rendered?
Updated background
tags_list is created by a fairly sophisticated process involving exec of some user provided text from a table/model field. The relevant portion of the real template looks like this:
{% for graph_row in graph_rows %}
<div class="row">
{% for graph in graph_row %}
<div class="col-md-{{ graph.width }}">
{{ graph.graph }}
</div>
{% endfor %}
</div>
{% endfor %}
The graph values look like this: {'graph':'{% piechart data1 %}', 'width':3}
Note that the order of entries in the context variable graph_rows is significant as is order of graph(s) in the row as that determines the placement of graphs on the page. Preserving this order is essential for the scheme to work correctly.
Currently, the view function simply does an {% include ... %} to get the template segment above to render in the correct order. This approach is simple and clean.
I could, as has been suggested, perform a template render within the view function but that complicates the design a bit and I'd hoped to avoid doing that if there is an easy way to trigger a render of {{ graph.graph }}. Note, as well, by moving the render into the view I loose the ability to easily take the template from arbitrary places, in particular table fields.
One of the great things about Django is the library of solution and code snippets. Sadly, they aren't a well organized and easy to find as one might wish. Nevertheless, a bit of google found a number of solutions of the general form
{% render tag.tag %}
Here are links to several:
render_as_template template tag
Allow template tags in a Flatpage's content
render_as_template.py
I'll use the general approach cleaned up a bit for error checking.
As an aside, the technique strikes me as generally useful and might be appropriate for inclusion in the standard tags.
Update 3/28/2014
After looking at the above and several others this is what I used from render_as_template template tag. There is a useful comment here.
from django import template
from django.template import Template, Variable, TemplateSyntaxError
register = template.Library()
class RenderAsTemplateNode(template.Node):
def __init__(self, item_to_be_rendered):
self.item_to_be_rendered = Variable(item_to_be_rendered)
def render(self, context):
try:
actual_item = self.item_to_be_rendered.resolve(context)
return Template(actual_item).render(context)
except template.VariableDoesNotExist:
return ''
def render_as_template(parser, token):
bits = token.split_contents()
if len(bits) !=2:
raise TemplateSyntaxError("'%s' takes only one argument"
" (a variable representing a template to render)" % bits[0])
return RenderAsTemplateNode(bits[1])
render_as_template = register.tag(render_as_template)
This gets part of the way to a solution. Unfortunately custom template tags, in my case
{% pie_chart %} are not available to render within the class RenderAsTemplateNode.
I've not tested this but it appears that this stack overflow question, Django - replacing built-in templatetag by custom tag for a whole site without {% load .. %}, points the way.
I believe I can provide a way for you to get the results you want, but there might be a better way for you to achieve the desired functionality if you can provide some context.
Anyway, you might do something like this in your view.py:
tags_list = [
Template('{% load my_tags %}{% ' + t.tag + ' %}').render(Context())
for t in tags_list
]
what does django do, when i do something like that in template
{{ object.parameter }}
I ask this because in case of arrayfields (postgresql array fields) it will print out either
{'value', 'value', 'value'}
(because thats how postgresql stores arrays in arrayfields)
or
['value','value','value']
if i use fields post_init method to convert postgresql array to python list.
Desired output would of course be value, value, value. I would rather not use some kind of filters for that, because then i would have to resort using IFs in templates or use some kind of template tag filter for every value i print out and that does not feel like a smart thing to do.
By the way, i know i can do something like that in template :
{% for choice in field.choices %}
{{ choice }}
{% if forloop.last %}
{% else %},
{% endif%}
{% endfor %}
and that gives me exactly what i want, but i thought there would be some other way doing it - with some modelfield method or something.
Alan
what does django do, when i do something like that in template
{{ object.parameter }}
See variables and lookups.
Desired output would of course be value, value, value. I would rather not use some kind of filters for that, because then i would have to resort using IFs in templates or use some kind of template tag filter for every value i print out and that does not feel like a smart thing to do.
You can make a really trivial filter:
#register.filter
def comma_join(values):
return u', '.join(values)
So simple:
{{ object.parameter|comma_join }}
Why would you want to avoid such a simple solution ?
and that gives me exactly what i want, but i thought there would be some other way doing it - with some modelfield method or something.
Of course you could also add such a method:
class YourModel(models.Model):
# ....
def comma_join_parameter(self):
return u', '.join(self.parameter)
And use it in your template as such:
{{ object.comma_join_parameter }}
I'm running a query to get the 5 latest News items. In my template, I want to display the first item in one location, then the remaining 4 further down the page.
In my template, I do something like this:
{% for n in news|slice:":1" %}
{{ n.headline }}
{% endfor %}
... more HTML ...
{% for n in news|slice:"1:" %}
{{ n.headline }}
{% endfor %}
When I look in the Debug Toolbar, this results in two queries to the database: one with LIMIT 1 and another with LIMIT 4 OFFSET 1, but otherwise the same. I appreciate this is Django's way of intelligently only requesting the stuff you actually use, but in this case it seems a little excessive. What's the best way to do this kind of thing?
Convert to a sequence in the view, then slice the sequence.
var = list(somequery[:5])
You just need to force the queryset to evaluate itself before the slice. This could be done as simply as calling len() on it in your view before passing it off to the context.
The Django docs have a complete list of everything that causes a queryset to evaluate. Just do something from that list and you're good.
This seems to me like a very simple question, but I can't seem to find the answer.
All I need to do is determine the number of objects returned by a database query.
The specific circumstance is this: I have a model named Student. This model has a ManyToManyField member named courses_current, which relates to a table of Course models. When I pass my Student instance to a template, I want to be able to do something like the following (the syntax may not be exact, but you'll get the basic idea):
<div id="classes">
{% if student.classes_current.all.size == 0 %}
<h1> HEY! YOU AREN'T TAKING ANY CLASSES! REGISTER NOW!
{% else %}
Here are your courses:
<!-- ... -->
{% endif %}
</div>
Now, I'm fairly certain that X_set.all.size is not a real thing. In the manage.py shell I can just use len(student.classes_current.all()), but I don't know of any way to use built-in functions, and "dictionary-like objects" don't have .size() functions, so I'm at a loss. I'm sure there's a very simple solution (or at least I hope there is), but I can't seem to find it.
{{ student.classes_current.all.count }} but be warned that it doesn't fetch the objects so you will need to do a separate query if you want to loop over them.
If you need loop over the classes for tag has way to get what you need.
{% for cl in student.current_classes.all %}
{{ cl }}
{% empty %}
<h1>Hey! ...</h1>
{% endfor %}
Documentation https://docs.djangoproject.com/en/dev/ref/templates/builtins/?from=olddocs#for-empty
I am trying to pass in url parameters to a django template like this...
response = render_to_string('persistConTemplate.html', request.GET)
This the calling line from my views.py file. persistConTemplate.html is the name of my template and request.GET is the dictionary that contains the url parameters.
In the template I try to use one of the parameters like this...
{% for item in (numItems) %}
item {{item}}
{% endfor %}
numItems is one of the url parameters that I am sending in my request like this...
http:/someDomain/persistentConTest.html/?numItems=12
When I try the for loop above, I get an output like this....
image 1 image 2
I am expecting and would like to see the word image printed 12 times...
image 1 image 2 image 3 image 4 image 5 image 6 image 7 image 8 image 9 image 10 image 11 image 12
Can anyone please tell me what I am going wrong?
you can coerce a str to an int using the add filter
{% for item in numItems|add:"0" %}
https://docs.djangoproject.com/en/dev/ref/templates/builtins/#add
to coerce int to str just use slugify
{{ some_int|slugify }}
EDIT: that said, I agree with the others that normally you should do this in the view - use these tricks only when the alternatives are much worse.
I like making a custom filter:
# templatetags/tag_library.py
from django import template
register = template.Library()
#register.filter()
def to_int(value):
return int(value)
Usage:
{% load tag_library %}
{{ value|to_int }}
It is for cases where this cannot be easily done in view.
Yes, the place for this is in the view.
I feel like the above example won't work -- you can't iterate over an integer.
numItems = request.GET.get('numItems')
if numItems:
numItems = range(1, int(numItems)+1)
return direct_to_template(request, "mytemplate.html", {'numItems': numItems})
{% for item in numItems %}
{{ item }}
{% endfor %}
The easiest way to do this is using inbuilt floatformat filter.
For Integer
{{ value|floatformat:"0" }}
For float value with 2 precision
{{ value|floatformat:"2" }}
It will also round to nearest value. for more details, you can check https://docs.djangoproject.com/en/1.10/ref/templates/builtins/#floatformat.
You should add some code to your view to unpack the GET params and convert them to the values you want. Even if numItems were an integer, the syntax you're showing wouldn't give you the output you want.
Try this:
ctx = dict(request.GET)
ctx['numItems'] = int(ctx['numItems'])
response = render_to_string('persistConTemplate.html', ctx)
In my case one of the items was a string and you can not compare a string to an integer so I had to coerce the string into an integer see below
{% if questions.correct_answer|add:"0" == answers.id %}
<span>Correct</span>
{% endif %}
You can do like that: if "select" tag used.
{% if i.0|stringformat:'s' == request.GET.status %} selected {% endif %}
My solution is kind of a hack and very specific..
In the template I want to compare a percentage with 0.9, and it never reaches 1, but all the values are considered string in the template, and no way to convert string to float.
So I did this:
{% if "0.9" in value %}
...
{% else %}
...
{% endif %}
If I want to detect some value is beyond 0.8, I must do:
{% if ("0.9" in value) or ("0.8" in value) %}
...
{% else %}
...
{% endif %}
This is a hack, but suffice in my case. I hope it could help others.