How can I increase page load speed? - django

Question

I need to have multilingual site. For this purpose I wrote django module, which collects lots of info about countries, cities and their translations to almost all languages.
Below is the short version of models of this module:
class LanguagesGroups(models.Model):
class Meta:
verbose_name = 'Language Group'
class Languages(models.Model):
iso_code = models.CharField("ISO Code", max_length=14, db_index=True)
group = models.ForeignKey(LanguagesGroups, on_delete=models.CASCADE, verbose_name='Group of ISO',
related_name='group', db_index=True)
class Cities(models.Model):
population = models.IntegerField(null=True)
territory_km2 = models.IntegerField(null=True)
class CitiesTranslations(models.Model):
common_name = models.CharField(max_length=188, db_index=True)
city = models.ForeignKey(Cities, on_delete=models.CASCADE, verbose_name='Details of City')
lang_group = models.ForeignKey(LanguagesGroups, on_delete=models.CASCADE, verbose_name='Language of city',
null=True)
class Meta:
index_together = (['common_name', 'city'],
['city', 'lang_group'])
I want to show to users some data about places which user requested with translated versions of cities (depending on user settings):
class Profile(models.Model):
title = models.CharField(_('title'), max_length=120)
info = models.TextField(_('information'), max_length=1500, blank=True)
city = models.ForeignKey(Cities, verbose_name=_('city'), null=True, blank=True)
def get_city(self):
user_lang = get_language() # en
lang_group = Languages.objects.get(iso_code=user_lang).group # 1823
return CitiesTranslations.objects.get(city=self.city, lang_group=lang_group).common_name
template.html
{% for item in object_list %}
{{ item.title }}
{{ item.get_city }}
{{ item.info }}
{% endfor %}
When I add {{ item.get_city }}, in case of pagination and just 25 items per page, the page load speed goes down up to 18 times and amount of queries (according to django-debug-tool) goes up from 2 to 102. django-debug-tool tells me about 25 duplications.
How can I fix this slowness?
EDIT:
My view
class ProfileListView(ListView):
model = Profile
template_name = 'profiles/profiles_list.html'
context_object_name = 'places_list'
paginate_by = 25

Answer 1

First of all, if you want speed - you should try caching.
You can also optimize your query.
def get_city(self):
user_lang = get_language() # en
return CitiesTranslations.objects.get(
city=self.city_id, lang_group__group__iso_code=user_lang
).common_name
What you probably also want is to get all your stuff in batches, not with individual method calls. Assuming we have your object_list:
city_ids = [x.city_id for x in object_list]
city_translations = CitiesTranslations.objects.filter(
city__in=city_ids, lang_group__group__iso_code=user_lang
).values_list('city_id', 'common_name')
city_translations = dict(city_translations)
for obj in object_list:
obj.city_name = city_translations[obj.city_id]
You can put this code somewhere in your view. You will also have to change {{ item.get_city }} to {{ item.city_name }} in the templates.