How to customise navigation menus¶

Customise menus at runtime¶

To adapt your menus according to request dependent conditions (say: anonymous/logged in user), you can use Navigation Modifiers or you can make use of existing ones.

For example it’s possible to add {'visible_for_anonymous': False}/{'visible_for_authenticated': False} attributes recognised by the django CMS core AuthVisibility modifier.

Complete example:

class UserMenu(Menu):
    def get_nodes(self, request):
            return [
                NavigationNode(_("Profile"), reverse(profile), 1, attr={'visible_for_anonymous': False}),
                NavigationNode(_("Log in"), reverse(login), 3, attr={'visible_for_authenticated': False}),
                NavigationNode(_("Sign up"), reverse(logout), 4, attr={'visible_for_authenticated': False}),
                NavigationNode(_("Log out"), reverse(logout), 2, attr={'visible_for_anonymous': False}),
            ]

Example use-cases¶

A simple example: you have a news application that publishes pages independently of django CMS. However, you would like to integrate the application into the menu structure of your site, so that at appropriate places a News node appears in the navigation menu.

In another example, you might want a particular attribute of your Pages to be available in menu templates. In order to keep menu nodes lightweight (which can be important in a site with thousands of pages) they only contain the minimum attributes required to generate a usable menu.

In both cases, a Navigation Modifier is the solution - in the first case, to add a new node at the appropriate place, and in the second, to add a new attribute - on the attr attribute, rather than directly on the NavigationNode, to help avoid conflicts - to all nodes in the menu.

How it works¶

Place your modifiers in your application’s cms_menus.py.

To make your modifier available, it then needs to be registered with menus.menu_pool.menu_pool.

Now, when a page is loaded and the menu generated, your modifier will be able to inspect and modify its nodes.

Here is an example of a simple modifier that places each Page’s changed_by attribute in the corresponding NavigationNode:

from menus.base import Modifier
from menus.menu_pool import menu_pool

from cms.models import Page

class MyExampleModifier(Modifier):
    """
    This modifier makes the changed_by attribute of a page
    accessible for the menu system.
    """
    def modify(self, request, nodes, namespace, root_id, post_cut, breadcrumb):
        # only do something when the menu has already been cut
        if post_cut:
            # only consider nodes that refer to cms pages
            # and put them in a dict for efficient access
            page_nodes = {n.id: n for n in nodes if n.attr["is_page"]}
            # retrieve the attributes of interest from the relevant pages
            pages = Page.objects.filter(id__in=page_nodes.keys()).values('id', 'changed_by')
            # loop over all relevant pages
            for page in pages:
                # take the node referring to the page
                node = page_nodes[page['id']]
                # put the changed_by attribute on the node
                node.attr["changed_by"] = page['changed_by']
        return nodes

menu_pool.register_modifier(MyExampleModifier)

It has a method modify() that should return a list of NavigationNode instances. modify() should take the following arguments:

request

A Django request instance. You want to modify based on sessions, or user or permissions?

nodes

All the nodes. Normally you want to return them again.

namespace

A Menu Namespace. Only given if somebody requested a menu with only nodes from this namespace.

root_id

Was a menu request based on an ID?

post_cut

Every modifier is called two times. First on the whole tree. After that the tree gets cut to only show the nodes that are shown in the current menu. After the cut the modifiers are called again with the final tree. If this is the case post_cut is True.

breadcrumb

Is this a breadcrumb call rather than a menu call?

Here is an example of a built-in modifier that marks all node levels:

class Level(Modifier):
    """
    marks all node levels
    """
    post_cut = True

    def modify(self, request, nodes, namespace, root_id, post_cut, breadcrumb):
        if breadcrumb:
            return nodes
        for node in nodes:
            if not node.parent:
                if post_cut:
                    node.menu_level = 0
                else:
                    node.level = 0
                self.mark_levels(node, post_cut)
        return nodes

    def mark_levels(self, node, post_cut):
        for child in node.children:
            if post_cut:
                child.menu_level = node.menu_level + 1
            else:
                child.level = node.level + 1
            self.mark_levels(child, post_cut)

menu_pool.register_modifier(Level)

Performance issues in menu modifiers¶

Navigation modifiers can quickly become a performance bottleneck. Each modifier is called multiple times: For the breadcrumb (breadcrumb=True), for the whole menu tree (post_cut=False), for the menu tree cut to the visible part (post_cut=True) and perhaps for each level of the navigation. Performing inefficient operations inside a navigation modifier can hence lead to big performance issues. Some tips for keeping a modifier implementation fast:

• Specify when exactly the modifier is necessary (in breadcrumb, before or after cut).

• Only consider nodes and pages relevant for the modification.

• Perform as less database queries as possible (i.e. not in a loop).

• In database queries, fetch exactly the attributes you are interested in.

• If you have multiple modifications to do, try to apply them in the same method.