Category: Python

Django `CheckboxSelectMultiple` with `ModelMultipleChoiceField` generates too many queries (solution)

13 September, 201413 September, 2014 simion Django, Programming, Python Leave a comment

If you use django.forms.ModelMultipleChoiceField with the default widget ( django.forms.widgets.SelectMultiple ), all’s good.

However, if you need to generate checkboxes for your choices, and use django.forms.widgets.CheckboxSelectMultiple you’ll notice that the field will generate alot of queries (one for each element in the queryset), which is really really bad. I personally ended up with hundred of queries.

Fix: add cache_choices=True to your django.forms.ModelMultipleChoiceField

Example:

Good practice:


test = forms.ModelMultipleChoiceField(
        queryset=MyModel.objects.all(),
        cache_choices=True,
        widget=forms.CheckboxSelectMultiple)

test = forms.ModelMultipleChoiceField(

queryset=MyModel.objects.all(),

cache_choices=True,

widget=forms.CheckboxSelectMultiple)

Bad practice:


test = forms.ModelMultipleChoiceField(
        queryset=MyModel.objects.all(),
        widget=forms.CheckboxSelectMultiple)

test = forms.ModelMultipleChoiceField(

queryset=MyModel.objects.all(),

widget=forms.CheckboxSelectMultiple)

Django get current user globally in the project

23 May, 201425 May, 2014 simion Django Leave a comment

Sometimes, you will need to get the current authenticated user in models, or other parts of your app.

To achieve this, you must create this middleware and add it to MIDDLEWARE_CLASSES in project settings:


try:
    from threading import local, current_thread
except ImportError:
    from django.utils._threading_local import local

_thread_locals = local()


class GlobalUserMiddleware(object):
    """
    Sets the current authenticated user in threading locals

    Usage example:
        from app_name.middleware import get_current_user
        user = get_current_user()
    """
    def process_request(self, request):
        setattr(
            _thread_locals,
            'user_{0}'.format(current_thread().name),
            request.user)

    def process_response(self, request, response):

        key = 'user_{0}'.format(current_thread().name)

        if not hasattr(_thread_locals, key):
            return response

        delattr(_thread_locals, key)

        return response


def get_current_user():
    return getattr(
        _thread_locals,
        'user_{0}'.format(current_thread().name),
        None)

try:

from threading import local, current_thread

except ImportError:

from django.utils._threading_local import local

_thread_locals = local()

class GlobalUserMiddleware(object):

"""

Sets the current authenticated user in threading locals

Usage example:

from app_name.middleware import get_current_user

user = get_current_user()

"""

def process_request(self, request):

setattr(

_thread_locals,

'user_{0}'.format(current_thread().name),

request.user)

def process_response(self, request, response):

key = 'user_{0}'.format(current_thread().name)

if not hasattr(_thread_locals, key):

return response

delattr(_thread_locals, key)

return response

def get_current_user():

return getattr(

_thread_locals,

'user_{0}'.format(current_thread().name),

None)

Usage example:


from myapp.middleware import get_current_user

user = get_current_user()

from myapp.middleware import get_current_user

user = get_current_user()

Invalidate template fragment cache in Django 1.5

21 May, 201421 May, 2014 simion Django, Python Leave a comment

Django 1.5 does not have a utility method to delete template fragment cache, with arguments.

In order to achieve this, you must create a custom method:


from django.core.cache import cache
from django.utils.hashcompat import md5_constructor
from django.utils.http import urlquote


def invalidate_template_fragment(fragment_name, *variables):
    args = md5_constructor(u':'.join([urlquote(var) for var in variables]))
    cache_key = 'template.cache.{0}.{1}'.format(fragment_name, args.hexdigest())
    cache.delete(cache_key)

from django.core.cache import cache

from django.utils.hashcompat import md5_constructor

from django.utils.http import urlquote

def invalidate_template_fragment(fragment_name, *variables):

args = md5_constructor(u':'.join([urlquote(var) for var in variables]))

cache_key = 'template.cache.{0}.{1}'.format(fragment_name, args.hexdigest())

cache.delete(cache_key)

Example usage:


{% cache 259200 key_name model_instance.pk %}
    ... cached content here ...
{% endcache %}

// note that "model_instance.pk" is optional argument. You can use as many as you need

{% cache 259200 key_name model_instance.pk %}

... cached content here ...

{% endcache %}

// note that "model_instance.pk" is optional argument. You can use as many as you need

… and delete the cache:


invalidate_template_fragment('key_name', model_instance.pk)

invalidate_template_fragment('key_name', model_instance.pk)

In django 1.6+ you can do this more easy:


from django.core.cache import cache
from django.core.cache.utils import make_template_fragment_key

key = make_template_fragment_key('key_name', [model_instance.pk])
cache.delete(key)

from django.core.cache import cache

from django.core.cache.utils import make_template_fragment_key

key = make_template_fragment_key('key_name', [model_instance.pk])

cache.delete(key)

Manually generate Django password reset token

7 March, 20147 March, 2014 simion Django, Programming, Python Leave a comment

Ever needed to manually generate a password reset token?

For example, imagine this situation:
You create a user from a custom form, and you want the user to set his own password.
Solution: generate a password reset token, email him the link, and let him choose his own password.

Here’s how you implement this:


from django.contrib.auth.tokens import default_token_generator
from django.utils.http import urlsafe_base64_encode
from django.utils.encoding import force_bytes

from django.db.models.signals import post_save

from django.contrib.auth.tokens import default_token_generator

from django.utils.http import urlsafe_base64_encode

from django.utils.encoding import force_bytes

from django.db.models.signals import post_save


post_save.connect(user_saved, User)

post_save.connect(user_saved, User)


def user_saved(sender, instance, created, *args, **kwargs):
    if created:
        context = {
            'token': default_token_generator.make_token(instance),
            'uid': urlsafe_base64_encode(force_bytes(instance.pk)),
            'user': instance,
        }
        # here, send an email with this context

def user_saved(sender, instance, created, *args, **kwargs):

if created:

context = {

'token': default_token_generator.make_token(instance),

'uid': urlsafe_base64_encode(force_bytes(instance.pk)),

'user': instance,

}

# here, send an email with this context

To display the link in the email, you must set the password reset url, and display it:


{% url 'password_reset_confirm' uidb64=uid token=token %}

{% url 'password_reset_confirm' uidb64=uid token=token %}


urlpatterns += patterns(
    'django.contrib.auth.views',
    url(r'^password-change/done/$', 'password_change_done', name='password_change_done'),
    url(r'^password-reset/confirm/(?P<uidb64>[0-9A-Za-z_\-]+)/(?P<token>[0-9A-Za-z]{1,13}-[0-9A-Za-z]{1,20})/$',
        'password_reset_confirm',
        name='password_reset_confirm'),
    url(r'^password-reset/done/$',
        'password_reset_done',
        name='password_reset_done'),
    url(r'^password-reset/complete/$',
        'password_reset_complete',
        name='password_reset_complete'),
)

urlpatterns += patterns(

'django.contrib.auth.views',

url(r'^password-change/done/$', 'password_change_done', name='password_change_done'),

url(r'^password-reset/confirm/(?P<uidb64>[0-9A-Za-z_\-]+)/(?P<token>[0-9A-Za-z]{1,13}-[0-9A-Za-z]{1,20})/$',

'password_reset_confirm',

name='password_reset_confirm'),

url(r'^password-reset/done/$',

'password_reset_done',

name='password_reset_done'),

url(r'^password-reset/complete/$',

'password_reset_complete',

name='password_reset_complete'),

)

Deploy with fabric on multiple servers

4 March, 20145 March, 2014 simion Programming, Python Leave a comment

Ever needed to deploy with fabric on multiple machines?
Here’s a simple solution to aproach this issue.

In your fabfile.py , add these two methods:


def live():
    global PATH, ENV_PATH
    env.hosts = ["22.2.222.2"]
    env.user = 'test'
    PATH = '/path/to/project'
    # optional, is using virtualenv
    ENV_PATH = '/path/to/virtualenv'
    # overwrite whatever variabled you need to change on the current machine

def staging():
    global PATH, ENV_PATH
    env.hosts = ["11.1.11.1"]
    env.user = 'test2'
    PATH = '/path/to/project/on/second/machine'
    # optional, is using virtualenv
    ENV_PATH = '/path/to/virtualenv'
    # overwrite whatever variabled you need to change on the current machine

def live():

global PATH, ENV_PATH

env.hosts = ["22.2.222.2"]

env.user = 'test'

PATH = '/path/to/project'

# optional, is using virtualenv

ENV_PATH = '/path/to/virtualenv'

# overwrite whatever variabled you need to change on the current machine

def staging():

global PATH, ENV_PATH

env.hosts = ["11.1.11.1"]

env.user = 'test2'

PATH = '/path/to/project/on/second/machine'

# optional, is using virtualenv

ENV_PATH = '/path/to/virtualenv'

# overwrite whatever variabled you need to change on the current machine

Now, when deploying, for example:


def deploy():
    with cd(PATH), virtualenv(ENV_PATH):
        run('uber command')
        run('another uber command')

def deploy():

with cd(PATH), virtualenv(ENV_PATH):

run('uber command')

run('another uber command')

you must use the following commands, in the correct order:


#deploy on staging
fab staging deploy

# deploy on live
fab live deploy

#deploy on staging

fab staging deploy

# deploy on live

fab live deploy

Fabric runs the “staging” or “deploy” commands first, setting the envrinoment variables, and then it runs the “deploy” command doing whatever you asked it to do.

Pip PIL error: Could not find any downloads that satisfy the requirement PIL

14 January, 201419 January, 2014 simion Python Leave a comment

When installing “PIL” with pip, I got this error:


Downloading/unpacking PIL
Could not find any downloads that satisfy the requirement PIL

Downloading/unpacking PIL

Could not find any downloads that satisfy the requirement PIL

Fix: use “Pillow” instead of “PIL”. Make sure you uninstall PIL first.


pip uninstall PIL
pip install Pillow

pip uninstall PIL

pip install Pillow

Compare integer variable in django templates

7 January, 201410 January, 2014 simion Django, Python 6 Comments

Ever needed to compare some variable (that may come from db, forms, etc) in django templates with an integer?
Example:


{% if some_var == 3 %}
    working
{% endif %}

{% if some_var == 3 %}

working

{% endif %}

The above example will not work. Django’s template engine interprets the variable as a string.

Workaround for integer comparison:


{% if some_var|add:0 == 3 %}
    working
{% endif %}

{% if some_var|add:0 == 3 %}

working

{% endif %}

By using the “add” filter, the variable is transformed into an integer.

Django emails with html/txt templates

10 October, 201310 October, 2013 simion Django, Programming, Python Leave a comment

Django Templated Email is a tool which sends email in django with html/txt templates.

Features:

Html / Txt templates
Context variables
Current site (from sites framework) available in templates as {{ site }} variable

Installation and usage:

Run the following command inside your django’s project directory