kmlxn · September 10, 2022 06:23
diff --git a/query_string.py b/query_string.py
 from django import template
 from collections import namedtuple

 register = template.Library()


 @register.tag
 def set_query_string_param(parser, token):
    """
    Django template tag to set/unset url query string parameter
    or replace parameter's value if it's already set

    ---------
    USAGE

    {% set_query_string_param <param_1_name> <param_1_value> <param_2_name> <param_2_value> ... %}

    tag takes even number of arguments

    param names and values may be context variables or strings

    if param value is empty string or None
    or variable that contain empty string or None,
    then that param will be removed from current url query string if present

    ---------
    EXAMPLE (page_num is context variable):

    src="{% set_query_string_param 'page' page_num %}"


    RESULT (if page_num = 3):

    (if query string was ?gender=male)
    src="?gender=male&page=3"

    (if query string was ?gender=male&page=2)
    src="?gender=male&page=3"

    (if there was no query string)
    src="?page=3"


    OTHER EXAMPLES

    src="{% set_query_string_param filter_name filter_value 'page' 3 %}"
    (if filter_name = gender, filter_value = male)
    src="?gender=male&page=3"

    src="{% set_query_string_param filter_name None 'page' page_num %}"
    (if filter_name = gender, page_num = 3, query string was ?gender=male&page=2)
    src="?page=3"

    ---------
    CAUTION

    if you remove all query string parameters through the tag, then it will
    return empty string. Like this (suppouse current query str = ?gender=male)
    <a href="{% set_query_string_param gender '' %}">
        Click on me and nothing will change
    </a>
    so if you click on such link, query string will stay ?gender=male.

    in such cases use it with {% url %} tag
    <a href="{% url 'catalog:filter' %}{% set_query_string_param gender '' %}">
        Click on me and reset filtering parameters
    </a>

    or tweak the script to return '?' instead of empty string - it will solve
    the problem

    ---------
    REQUIRES to set this in settings.py:

    TEMPLATES = [{
        ...
        'OPTIONS': {
            ...
            'context_processors': [
                ...
                'django.core.context_processors.request',
                ...
            ],
            ...
        },
        ...
    }]
    """

    params = get_tag_args(token)

    return QueryStringSetValueNode(params)


 def get_tag_args(token):
    arguments = token.split_contents()
    del arguments[0]  # delete tag name

    if len(arguments) < 2 or len(arguments) % 2 != 0:
        raise template.TemplateSyntaxError(
            "%r tag requires even number of argument (min 2)" % token.contents.split()[0]
        )

    TagArgsPair = namedtuple('TagArgsPair',
        ['str_repr_of_name_param', 'str_repr_of_value_param'])

    tag_args = [TagArgsPair(arguments[x], arguments[x + 1])
        for x in range(0, len(arguments), 2)]

    return tag_args


 class QueryStringSetValueNode(template.Node):
    def __init__(self, tag_args):
        self.tag_args = tag_args


    def render(self, context):
        query_string_params = context.request.GET.copy()
        query_string_params_to_set = self.evaluate_query_string_params(context)

        return self.make_query_string(query_string_params, query_string_params_to_set)


    @staticmethod
    def make_query_string(query_string_params, query_string_params_to_set):
        for name, value in query_string_params_to_set.items():
            if (value == '' or value is None):
                query_string_params.pop(name, None)
            else:
                query_string_params[name] = value

        if not query_string_params:
            return ''
        return '?' + query_string_params.urlencode()


    def evaluate_query_string_params(self, context):
        return {
            self.evaluate_tag_arg(context, x.str_repr_of_name_param):
            self.evaluate_tag_arg(context, x.str_repr_of_value_param)
            for x in self.tag_args
        }


    def evaluate_tag_arg(self, context, tag_argument):
        if self.represents_string(tag_argument):
            value = tag_argument[1:-1]
        else:
            value = self.get_variable_value_from_template_context(context, tag_argument)

        return value


    @staticmethod
    def represents_string(tag_argument):
        if tag_argument[0] == tag_argument[-1] and tag_argument[0] in ('"', "'"):
            return True
        return False


    @staticmethod
    def get_variable_value_from_template_context(context, variable_name):
        var = template.Variable(variable_name)

        return var.resolve(context)
	from django import template
	from collections import namedtuple

	register = template.Library()


	@register.tag
	def set_query_string_param(parser, token):
	"""
	Django template tag to set/unset url query string parameter
	or replace parameter's value if it's already set

	---------
	USAGE

	{% set_query_string_param <param_1_name> <param_1_value> <param_2_name> <param_2_value> ... %}

	tag takes even number of arguments

	param names and values may be context variables or strings

	if param value is empty string or None
	or variable that contain empty string or None,
	then that param will be removed from current url query string if present

	---------
	EXAMPLE (page_num is context variable):

	src="{% set_query_string_param 'page' page_num %}"


	RESULT (if page_num = 3):

	(if query string was ?gender=male)
	src="?gender=male&page=3"

	(if query string was ?gender=male&page=2)
	src="?gender=male&page=3"

	(if there was no query string)
	src="?page=3"


	OTHER EXAMPLES

	src="{% set_query_string_param filter_name filter_value 'page' 3 %}"
	(if filter_name = gender, filter_value = male)
	src="?gender=male&page=3"

	src="{% set_query_string_param filter_name None 'page' page_num %}"
	(if filter_name = gender, page_num = 3, query string was ?gender=male&page=2)
	src="?page=3"

	---------
	CAUTION

	if you remove all query string parameters through the tag, then it will
	return empty string. Like this (suppouse current query str = ?gender=male)
	<a href="{% set_query_string_param gender '' %}">
	Click on me and nothing will change
	</a>
	so if you click on such link, query string will stay ?gender=male.

	in such cases use it with {% url %} tag
	<a href="{% url 'catalog:filter' %}{% set_query_string_param gender '' %}">
	Click on me and reset filtering parameters
	</a>

	or tweak the script to return '?' instead of empty string - it will solve
	the problem

	---------
	REQUIRES to set this in settings.py:

	TEMPLATES = [{
	...
	'OPTIONS': {
	...
	'context_processors': [
	...
	'django.core.context_processors.request',
	...
	],
	...
	},
	...
	}]
	"""

	params = get_tag_args(token)

	return QueryStringSetValueNode(params)


	def get_tag_args(token):
	arguments = token.split_contents()
	del arguments[0] # delete tag name

	if len(arguments) < 2 or len(arguments) % 2 != 0:
	raise template.TemplateSyntaxError(
	"%r tag requires even number of argument (min 2)" % token.contents.split()[0]
	)

	TagArgsPair = namedtuple('TagArgsPair',
	['str_repr_of_name_param', 'str_repr_of_value_param'])

	tag_args = [TagArgsPair(arguments[x], arguments[x + 1])
	for x in range(0, len(arguments), 2)]

	return tag_args


	class QueryStringSetValueNode(template.Node):
	def __init__(self, tag_args):
	self.tag_args = tag_args


	def render(self, context):
	query_string_params = context.request.GET.copy()
	query_string_params_to_set = self.evaluate_query_string_params(context)

	return self.make_query_string(query_string_params, query_string_params_to_set)


	@staticmethod
	def make_query_string(query_string_params, query_string_params_to_set):
	for name, value in query_string_params_to_set.items():
	if (value == '' or value is None):
	query_string_params.pop(name, None)
	else:
	query_string_params[name] = value

	if not query_string_params:
	return ''
	return '?' + query_string_params.urlencode()


	def evaluate_query_string_params(self, context):
	return {
	self.evaluate_tag_arg(context, x.str_repr_of_name_param):
	self.evaluate_tag_arg(context, x.str_repr_of_value_param)
	for x in self.tag_args
	}


	def evaluate_tag_arg(self, context, tag_argument):
	if self.represents_string(tag_argument):
	value = tag_argument[1:-1]
	else:
	value = self.get_variable_value_from_template_context(context, tag_argument)

	return value


	@staticmethod
	def represents_string(tag_argument):
	if tag_argument[0] == tag_argument[-1] and tag_argument[0] in ('"', "'"):
	return True
	return False


	@staticmethod
	def get_variable_value_from_template_context(context, variable_name):
	var = template.Variable(variable_name)

	return var.resolve(context)
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