# Command Signals

synopsis

  Signals fired before and after a command is executed.

A signal is thrown pre/post each management command allowing your application to hook into each commands execution.

## Basic Example

An example hooking into show_template_tags:

    from django_extensions.management.signals import pre_command, post_command
    from django_extensions.management.commands.show_template_tags import Command

    def pre_receiver(sender, args, kwargs):
      # I'm executed prior to the management command

    def post_receiver(sender, args, kwargs, outcome):
      # I'm executed after the management command

    pre_command.connect(pre_receiver, Command)
    post_command.connect(post_receiver, Command)

## Custom Permissions For All Models

You can use the post signal to hook into the `update_permissions` command so that you can add your own permissions to each model.

For instance, lets say you want to add `list` and `view` permissions to each model. You could do this by adding them to the `permissions` tuple inside your models `Meta` class but this gets pretty tedious.

An easier solution is to hook into the `update_permissions` call, as follows;

    from django.db.models.signals import post_syncdb
    from django.contrib.contenttypes.models import ContentType
    from django.contrib.auth.models import Permission
    from django_extensions.management.signals import post_command
    from django_extensions.management.commands.update_permissions import Command as UpdatePermissionsCommand

    def add_permissions(sender, **kwargs):
      """
      Add view and list permissions to all content types.
      """
      # for each of our content types
      for content_type in ContentType.objects.all():

        for action in ['view', 'list']:
          # build our permission slug
          codename = "%s_%s" % (action, content_type.model)

          try:
            Permission.objects.get(content_type=content_type, codename=codename)
            # Already exists, ignore
          except Permission.DoesNotExist:
            # Doesn't exist, add it
            Permission.objects.create(content_type=content_type,
                          codename=codename,
                          name="Can %s %s" % (action, content_type.name))
            print "Added %s permission for %s" % (action, content_type.name)
    post_command.connect(add_permissions, UpdatePermissionsCommand)

Each time `update_permissions` is called `add_permissions` will be called which ensures there are view and list permissions to all content types.

## Using pre/post signals on your own commands

The signals are implemented using a decorator on the handle method of a management command, thus using this functionality in your own application is trivial:

    from django_extensions.management.utils import signalcommand

    class Command(BaseCommand):

      @signalcommand
      def handle(self, *args, **kwargs):
        ...
        ...