Django: variable in variable in templates

Question

Let's assume the following situation. In my database (model) I have a field of description of the task for students. Each student should have their own variant of some variables in the task. So, I save the following model named task in the database:

 id | name | description |
 ---+---------+----------------------------------------------+
 1 | Simple | This is first task. Answer is {{student_var}}|

Method for the view is simple (TeamFlag is a table to correlate teams and tasks:

def render_team(request, team):
 tasks = TeamFlag.objects.filter(team=team)
 return render(request,
 'team.html',
 dict({'team': team,
 'tasks': tasks,
 'student_var': 'foo',
 }))

In my template:

{% for team_task in tasks %}
 <li class="item">
 <h6>{{ team_task.task.name }}</h6>
 <div class="task-content">{% autoescape off %}
 {{team_task.task.description }}
 {% endautoescape %}</div>

As the result I see:

 This is first task. Answer is {{student_var}}

Is there any way in Django to pre-process variables, which are inside the string and pass processed HTML string to the view inside the template, basing on variables (I plan to keep variables in database in K-V format in table with fields like: id, key, value, team_id, task_id).

Generally, I would like to have some method like process_template(html_string, kv-data), which returns processed HTML string or something similar. I heard about custom filters for the templates, but I'm not sure, whether it's the case or not.

UPD: I successfully added the following code:

tasks = TeamFlag.objects.filter(team=team)
for tf in tasks:
 data = TaskData.objects.filter(team=team, task=tf.task)
 tf.task.description = Template(tf.task.description).render(
 Context(dict(zip([x.key for x in data],
 [x.value for x in data]))))

However, Django now ignores layout in tf.task.description. My new description looks like:

I have some {{temp}} <b>here</b> and it's {{temp2}}

It's being rendered, I can see it in source code of the page, but actually nothing happens.

UPD2: Seems to be CSS problem. Question closed.

Answer 1

For a helper method, you could create something with Template and Context

from django.template import Template, Context
def process_template(tasks, student_var):
 new_tasks = []
 for team_task in tasks:
 template = Template(team_task.task.description)
 context = Context({'student_var': student_var})
 rendered_template = template.render(context)
 team_task.task.description = rendered_template
 new_tasks.append(team_task)
 return new_tasks
def render_team(request, team):
 tasks = process_template(TeamFlag.objects.filter(team=team))

You can take a look at the documentation for more info.

• vladfau: I updated fields in models, but not saved them, so there've not been any change in database, though updated models were properly passed to the template: for tf in tasks: template = Template(tf.task.description) context = Context({'temp': '123'}) tf.task.description = template.render(context)

Answer 2

The template processor is just code. It accepts a string, parses it, and populates it according to the context it is given. The string can just as easily come from the database as from a file on disk.

At its root it is as simple as:

from django.template import Template, Context
tpl = Template(task.description)
output = tpl.render(tpl, Context({'student_var': 'foo'}))

Where you put this is up to you. It could be a model method, or a template filter. One question you don't answer is where the variables are coming from; if there is only student_var, you can pass that in to the filter explicitly; if not you'll have to work out where to get them from.

• vladfau: All student_var-like variables will come from database and corresponding model. What about the string, which comes from model as well? I need just to put it into Context as well?
• Daniel Roseman: I don't understand what you're asking. What string?
• vladfau: task.description string
• Daniel Roseman: But haven't I shown that in the answer? You pass that into the Template instantiation, it's not part of the context.
• vladfau: Okay, I'll try it and report my results. I just don't want to do rendering on my own

Answer 3

You can create a simple tag and use that in django template like below:

{% my_custom_filter team_task.task.description %}

from django.template import Context, Template
@register.simple_tag(name='my_custom_filter', takes_context=True)
def my_custom_filter(context, val):
 template = Template(val)
 context = Context(context)
 final_val = template.render(context)
 return final_val