django-querystring-tag

This tiny package adds the {% querystring %} tag: A powerful, well tested template tag for modifying and rendering safe, suitably-encoded querystring values.

It's the clean and simple way to create pagination links, filters and other state-preserving links, without cluttering up your view code!

Installation

1. Install the package from pypi:

   With Poetry

   $ poetry add django-querystring-tag

   With pip

   $ pip install django-querystring-tag

2. Add "querystring_tag" to the INSTALLED_APPS list in your Django project settings.

Add querystring_tag to builtins (optional)

To use the {% querystring %} tag freely, without having to add {% load querystring_tag %} to all of your templates, you can add "querystring_tag.templatetags.querystring_tag" to the ['OPTIONS']['builtins'] list for your chosen template backend. Here's an example.

How to use

First, load the tag into the template you want to use it in:

{% load querystring_tag %}

You can then use the tag like this:

{% querystring param_one='value' param_two+='add-to-existing' param_three-="remove-from-existing" %}

The basics

1. The tag uses request.GET as the data source by default. Check out the source_data option if you have other ideas.
2. The examples below are deliberately simple: You can make as many modifications in the same tag as you need. GO CRAZY!
3. You may be wondering "I want to use this in an include template, where the parameter name is dynamic. Will that work?". Yes it will! I know it's unusual, but you can use tempalate variables for parameter names too.
4. You don't want to preserve Google tracking parameters in links, do you? I thought not. Any parameters starting with utm_ are removed by default. Add remove_utm=False if you would rather keep them.
5. You're probably not interested in preserving blank parameters in links either, are you? See? I read your mind! Blank values are removed by default too. Add remove_blank=False if you would rather keep them.
6. Want to variabalize the return value instead of rendering it? Go ahead and try the as option - It works just as you would expect.

Use = to set or replace a parameter

The most common requirement is to completely replace the value for a specific parameter. This is done using a regular keyword argument, with an = operator between the parameter name and value. For example, if your querystring looked like this:

?q=test&baz=1

And you wanted to add a foo variable with the value bar, your querystring tag might look like this:

{% querystring foo="bar" %}

Which would result in the following output:

?q=test&baz=1&foo=bar

Use -= to remove values from a multi-value parameter

When working with multi-value parameters, you may find yourself having to remove a specific value, without affecting any of the others.

In these situations, you can use the -= operator instead of the usual =. For example, if the current querystring looked something like this:

?q=test&bar=1&bar=2&bar=3

And you wanted to remove &bar=2, your querystring tag might look like this:

{% querystring bar-=2 %}

Which would result in the following output:

?q=test&bar=1&bar=3

If the specified value isn't present, the instruction will simply be ignored.

Use += to add values to a multi-value parameter

When working with multi-value parameters, you may find yourself having to add a specific value for a parameter, without affecting any of the others.

In these situations, you can use the += operator instead of the usual =. For example, if the current querystring looked something like this:

?q=test&bar=1&bar=2&bar=3

And you wanted to add &bar=4, your querystring tag might look like this:

{% querystring bar+=4 %}

Which would result in the following output:

?q=test&bar=1&bar=2&bar=3&bar=4

If the specified value is already present, the instruction will simply be ignored.

Use only to specify parameters you want to keep

Use only at the start of your {% querystring %} tag when you want the querystring to include values for specific parameters only.

For example, say the current querystring looked like this:

?q=keywords&group=articles&category=2&published_after=2022-01-01

And you only wanted to include the q and group params in a link. You could do:

{% querystring only 'q' 'group' %}

Which would result in the following output:

?q=keywords&group=articles

You can combine only with any number of modifications too. Just be sure to keep the only keyword and related parameter names as the left-most parameters, like so:

{% querystring only 'q' group="group_value" clear_session="true" %}

Use discard to specify parameters you want to lose

Use discard at the start of your {% querystring %} tag when you want to exclude specific parameters from the querystring.

For example, say the current querystring looked like this:

?q=keywords&group=articles&category=2&published_after=2022-01-01

And you wanted to preserve everything except for group published_after. You could do:

{% querystring discard 'group' 'published_after' %}

Which would result in the following output:

?q=keywords&group=articles

You can combine discard with any number of modifications too. Just be sure to keep the discard keyword and related parameter names as the left-most parameters, like so:

{% querystring discard 'published_after' group="group_value" clear_session="true" %}

Using template variables for parameter names

Unlike a lot of custom template tags, {% querystring %} supports the use of template variables in keys as well as values. For example, if the tag was being used to generate pagination links, and page_param_name and page_num were variables available in the template, you could use them both like so:

{% querystring page_param_name=page_num %}

Supported value types

Values can be strings, booleans, integers, dates, datetimes, Django model instances, or iterables of either of these values.

When encountering a Django model instance, {% querystring %} will automatically take the pk value from it, and use that to modify the querystring. To use a different field value, you can use the tag's model_value_field option (see further down for details). Alternatively, you can add a querystring_value_field attribute to your model class. For example:

class Category(models.Model):
    name = models.CharField(max_length=50)
    slug = models.SlugField(max_length=50, unique=True)

    # use 'slug' values in querystrings
    querystring_value_field = "slug"

Specifying multiple values

As mentioned above, you can provide an iterable as a value to specify multiple values for a parameter at once. That could be a native Python type, such as a list, tuple or set, but could also be anything that implements the __iter__ method to support iteration, for example, a QuerySet.

For example, if the context contained a variable tag_list, which was list of strings (['tag1', 'tag2', 'tag3']), you can include all of those values by referencing the list value. For example:

{% querystring tags=tag_list %}

The output of the above would be:

"?tags=tag1&tags=tag2&tags=tag3"

Options reference

source_data

Supported value types: QueryDict, dict, str

Default value: request.GET

The tag defaults to using request.GET as the data source for the querystring, but the source_data keyword argument can be used to specify use an alternative QueryDict, dict or string value.

For example, say you were using a Django form to validate query data, and only want valid data to be included. You could use the Form's cleaned_data to generate a querystring instead:

{% querystring source_data=form.cleaned_data page=2 %}

remove_blank

Supported value types: bool

Default value: True

Any parameter values with a value of None or "" (an empty string) are removed from the querystring default.

To retain blank values, include remove_blank=False in your {% querystring %} tag.

remove_utm

Supported value types: bool

Default value: True

Parameter names starting with "utm_" (the format used for Google Analytics tracking parameters) are exluded from the generated querystrings by default, as it's unlikley that you'll want these to be repeated in links to other pages.

To retain these parameters instead, include remove_utm=False in your {% querystring %} tag.

model_value_field

Supported value types: str

Default value: "pk"

By default, when encountering a Django model instance as a value, {% querystring %} will take the pk value from the instance to use in the querystring. If you'd like to use a different field value, you can use the model_value_field option to specify an alternative field.

For example, if the model had a slug field that you were using as the public-facing identifier, you could specify that slug values be used in the querystring, like so:

{% querystring tags=tag_queryset model_field_value='slug' %}

Testing the code locally

If you have a recent version of Python 3 installed, you can use a simple virtualenv to run tests locally. After cloning the repository, navigate to the project's root directory on your machine, then run the following:

Set up the virtualenv

$ virtualenv venv
$ source venv/bin/activate
$ pip install -e '.[test]' -U

Run tests

$ pytest

When you're done

$ deactivate