Part 4: Useful tricks

Here I’ll try show some useful trick that can save you time and explain how Django RPC works.

Real examples of code you can find in example project, tricks app.

Passing extra arguments

Real situation is when you need access to Django request object in your RPC method. My idea was do not pass request to hide how we do method call. So in future we can use our action class for some other API or send request via WebSocket+Torando (In current version you can’t do this, but with a little patching I did for one project).

I’ll show you few ways how to pass extra arguments from request to our methods.

Router level

You can subclass djangorpc.RpcRouter and rewrite extra_kwargs method. Original method looks like this:

def extra_kwargs(self, request, *args, **kwargs):
    return {
        'user': request.user
    }

You can see *args and **kwargs. This is important here. These are arguments parsed with Django URL patterns that are passed to views. So you can get some ID from URL and pass it to every method. You will see this later.

Lets add request here:

from djangorpc import RpcRouter, Error, Msg

class CustomRouter(RpcRouter):

    def extra_kwargs(self, request, *args, **kwargs):
        print args, kwargs
        return {
            'request': request,
            'user': request.user
        }

custom_router = CustomRouter()

Now create some actions classes for testing. Do not forget about new request arguments:

class TricksApiClass(object):

    def func1(self, user, request):
        return Msg(u'func1')


class TricksOneApiClass(object):

    def func2(self, val, **kwargs):
        return Msg(u'func2')

And add theme to our router:

custom_router = CustomRouter(
    {
        'TricksApi': TricksApiClass(),
        'TricksOneApi': TricksOneApiClass()
    },
    url_namespace='tricks:custom_rpc')

Just to have full example, lets show urls.py:

from django.conf.urls import patterns, include, url
from .rpc import custom_router


urlpatterns = patterns('example.tricks.views',
    url(r'^$', 'index', name='index'),
    url(r'^custom_rpc/', include(custom_router.urls, 'custom_rpc')),
)

and our template:

<script src="{% url 'tricks:custom_rpc:jsapi' %}"></script>
<script>
    TricksApi.func1(function(response){
        console.log(response.msg);
    });

    TricksOneApi.func2(1, function(response){
        console.log(response.msg);
    });
</script>

It works, every method get request object.

Action level

You can add _extra_kwargs method for action class. It works like router level:

class TricksTwoApiClass(object):

    def func3(self, user, request):
        return Msg(u'func3')

    def _extra_kwargs(self, request, *args, **kwargs):
        return {
            'request': request,
            'user': request.user
        }

Method level

You can add _extra_kwargs attribute for method:

def extra_kwargs(request, *args, **kwargs):
    return {
        'request': request,
        'user': request.user
    }


class TricksThreeApiClass(object):

    def func4(self, user, request):
        return Msg(u'func4')

    func4._extra_kwargs = extra_kwargs

Or you can use add_request_to_kwargs() decorator.

RpcExceptionEvent

To raise exception event in client, you can use RpcExceptionEvent. For example:

class TricksThreeApiClass(object):

    def func6(self, user):
        if not user.is_authenticated():
            raise RpcExceptionEvent('Login please!')

and catch it with javascript:

jQuery.Rpc.on('exception', function(event){
    alert('Error during RPC request: '+event.message);
});

For required login you use decorator login_required().

Passing arguments from URL

This tricks allow add argument from URL to every RPC request without changing any JS code.

Why may you need this?

For instance, we have some browser game. User can create battle, other can join this battle and everything happens on page with URL ‘/battle/100500/’, where 100500 is ID of some row in out battle table in database.

You do not want pass battle ID for every RPC call, especially if your GameApi.move, GameApi.hit, GameApi.jump, GameApi.next_turn and other are used a lot in your JS.

What to do?

Django RPC allows you easy pass extra arguments(our battle_id) in URL. All these arguments are passed to method, that allows you pass extra arguments.

Example

At first let our URL-patterns accept arguments from URL:

urlpatterns = patterns('example.game.views',
    url(r'^battle/(?P<battle_id>\d+)/$', 'battle', name='battle'),
    url(r'^rpc/(?P<battle_id>\d+)/', include(router.urls, 'rpc')),
)

battle view is not related to RPC, just want to show how harmoniously it is.

Our actions.py can be like this:

from djangorpc import RpcRouter, Error, Msg
from djangorpc.exceptions import RpcExceptionEvent


class GameApiClass(object):

    def move(self, x, y, battle, user):
        battle.move(x, y, user)
        return {}

    def _extra_kwargs(self, request, *args, **kwargs):
        try:
            battle = Battle.objects.get(pk=kwargs['battle_id'])
        except Battle.DoesNotExist:
            raise RpcExceptionEvent('Invalid battle id!')

        return {
            'battle': battle
        }

router = RpcRouter(
    {
        'GameApi': GameApiClass(),
    },
    url_namespace='game:rpc')

And in our template just use battle_id to create URL to our rpc script:

<script src="{% url 'game:rpc:jsapi' battle_id %}"></script>
<script>
    GameApi.move(1, 2);
</script>

_pre_execute

If method has _pre_execute attribute, it is executed before method call. It can be use to make some validation. For now it is used for login_required() decorator. You can use it to create own decorators.