Customizing your application

Usually you won’t get enough by assembling cubes out-of-the-box. You will want to customize them to get personal look and feel, add your own data model and so on. Or maybe start from scratch?

So let’s get a bit deeper and start coding our own cube. In our case, we want to customize the blog we created to add more features to it.

Creating your own cube

Once your CubicWeb development environment is set up, you can create a new cube:

cubicweb-ctl newcube mycube

This will create a a directory named cubicweb-mycube reflecting the structure described in Standard structure for a cube.

To install your new cube on the virtual environment created previously, run the following command in cubicweb-mycube directory:

pip install -e .

All cubicweb-ctl commands are described in details in cubicweb-ctl tool.

Cube metadata

The folder cubicweb_mycube/ contains the actual code and metadata for your cube. In this folder, a simple set of metadata about your cube are stored in the __pkginfo__.py file. In our case, we want to extend the blog cube, so we have to tell that our cube depends on this cube by modifying the __depends__ dictionary in that file:

__depends__ =  {"cubicweb": ">= 3.35.0", "cubicweb-blog": None}

where None means we do not depend on a particular version of the cube.

Extending the data model

The data model or schema is the core of your CubicWeb application. It defines the type of content your application will handle. It is defined in the file schema.py of the cube.

Defining our model

Let’s say we want a new entity type named Community with a name and a description. A Community will hold several blogs.

We can edit the schema.py as follows:

from yams.buildobjs import EntityType, RelationDefinition, String, RichString

class Community(EntityType):
    name = String(maxsize=50, required=True)
    description = RichString()

class community_blog(RelationDefinition):
    subject = 'Community'
    object = 'Blog'
    cardinality = '*?'
    composite = 'subject'

The import from the yams package provides necessary classes to build the schema.

This file defines the following:

• a Community has a name and a description as attributes

  • the name is a string which is required and cannot be longer than 50 characters

  • the description is an unconstrained string and may contains rich content such as HTML or Restructured text.

• a Community may be linked to a Blog using the community_blog relation

  • * means a community may be linked from 0 to N blog, ? means a blog may be linked to 0 to 1 community. For completeness, you can also use + for 1 to N, and 1 for a single mandatory relation (e.g. one to one);

  • this is a composite relation where Community (e.g. the subject of the relation) is the composite. That means that if you delete a community, its blog will be deleted as well.

Of course, there are a lot of other data types and relations such as constraints, permissions, etc, that may be defined in the schema but those will not be covered in this tutorial.

Notice that our schema refers to the Blog entity type which is not defined here. But we know this type is available since we depend on the blog cube defining it.

Applying changes from the model into our instance

The problem is that we created an instance using the blog cube, not our mycube cube. If we do not do anything there is no way we’ll see anything changing in the myblog instance.

As we do not have any really valuable data in the instance, an easy way would be to trash it and recreated it. First stop the running instance by pressing Ctrl-C in the terminal running the server in debug mode. Then run the following commands:

cubicweb-ctl delete myblog
cubicweb-ctl create mycube myblog
cubicweb-ctl start -D myblog

Another way is to add our cube to the instance using the cubicweb-ctl shell facility. It is a python shell connected to the instance with some special commands available to manipulate it (the same as you’ll have in migration scripts, which are not covered in this tutorial). In that case, we are interested in the add_cube command. First stop the instance by pressing Ctrl-C in the terminal running the server in debug mode and enter the shell using the following command:

cubicweb-ctl shell myblog

Then in the python shell, type the add_cube command:

add_cube('mycube')

Press Ctrl-D to exit then restart your instance:

cubicweb-ctl start -D myblog

The add_cube command is enough since it automatically updates our application to the cube’s schema. There are plenty of other migration commands of a more finer grain. They are described in Migration

If you take another look at the schema on your instance, you will see that changes to the data model have actually been applied (meaning database schema updates and all necessary actions have been done).

If you follow the Site information link in the home page, you will also see that the instance is using blog and mycube cubes (sioc is a dependency of the blog cube).

You can now add some communities and link them to a blog. You will see that the framework provides default views for this entity type (we have not yet defined any view for it!), and also that the blog primary view will show the community it is linked to if any. All this thanks to the model driven interface provided by the framework.

We will now see how to redefine each of them according to your needs and preferences.

Defining your views

CubicWeb provides a lot of standard views in the directory cubicweb/web/views/. We already talked about primary and list views, which are views applying to one or more entities.

A view is defined by a python class which includes:

• an identifier: all objects used to build the user interface in CubicWeb are recorded in a registry and this identifier will be used as a key in that registry to store the view. There may be multiple views for the same identifier.

• a selector, which is a kind of filter telling how well a view suits to a particular context. When looking for a particular view (e.g. given an identifier), CubicWeb computes for each available view with that identifier a score which is returned by the selector. Then the view with the highest score is used. The standard library of predicates is in cubicweb.predicates.

A view has a set of methods inherited from the cubicweb.view.View class, though you do not usually derive directly from this class but from one of its more specific child class.

Last but not least, CubicWeb provides a set of default views accepting any kind of entities.

To illustrate this, we will create a community as we already have done for other entity types through the index page. You will get a screen similar to this:

Changing the layout of the application

The layout is the general organization of the pages in the website. Views generating the layout are sometimes referred to as templates. They are implemented by the framework in the module cubicweb.web.views.basetemplates. By overriding classes in this module, you can customize whatever part you wish of the default layout.

CubicWeb provides many other ways to customize the interface thanks to actions and components (which you can individually (de)activate, control their location, customize their look…) as well as “simple” CSS customization. You should first try to achieve your goal using such fine grained parametrization rather then overriding a whole template, which usually embeds customisation access points that you may loose in the process.

But for the sake of example, let’s say we want to change the generic page footer. We can simply add in the file cubicweb_mycube/views.py the code below:

from cubicweb.web.views import basetemplates


class MyHTMLPageFooter(basetemplates.HTMLPageFooter):

    def footer_content(self):
        self.w(u'This website has been created with <a href="http://cubicweb.org">CubicWeb</a>.')


def registration_callback(vreg):
    vreg.register_all(globals().values(), __name__, (MyHTMLPageFooter,))
    vreg.register_and_replace(MyHTMLPageFooter, basetemplates.HTMLPageFooter)

• Our class inherits from the default page footer to ease getting things right, but this is not mandatory.

• When we want to write something to the output stream, we simply call self.w, which must be passed a unicode string.

• Since both HTMLPageFooter and MyHTMLPageFooter have the same selector, hence the same score the framework would not be able to choose which footer to use. In this case we want our footer to replace the default one, so we have to define a registration_callback() function to control object registration. The first instruction tells to register everything in the module but the MyHTMLPageFooter class, then the second to register it instead of HTMLPageFooter. Without this function, everything in the module is registered blindly.

Note

When a view is modified while running in debug mode, it is not required to restart the instance server. Save the Python file and reload the page in your web browser to view the changes.

You will now see this simple footer on every page of the website.

Primary view customization

The primary view (i.e. any view with the identifier set to primary) is the one used to display all the information about a single entity. The standard primary view is one of the most sophisticated views of all. It has several customisation points, but its power comes with uicfg allowing you to control it without having to subclass it.

However this is a bit off-topic for this first tutorial. Let’s say we simply want a custom primary view for the Community entity type, using directly the view interface without trying to benefit from the default implementation (you should do that though if you’re rewriting reusable cubes; everything is described in more details in The Primary View).

here is the code that we will put in the file cubicweb_mycube/views.py of our cube:

from cubicweb.predicates import is_instance
from cubicweb.web.views import primary


class CommunityPrimaryView(primary.PrimaryView):
    __select__ = is_instance('Community')

    def cell_call(self, row, col):
        entity = self.cw_rset.get_entity(row, col)
        self.w(u'<h1>Welcome to the "%s" community</h1>' % entity.printable_value('name'))

        if entity.description:
            self.w(u'<p>%s</p>' % entity.printable_value('description'))

What’s going on here?

• Our class inherits from the default primary view, here mainly to get the correct view identifier, since we do not use any of its features.

• We set on it a selector telling that it only applies when trying to display some entity of the Community type. This is enough to get an higher score than the default view for entities of this type.

• A view that applies to an entity usually has to define the method cell_call as an entry point. This receives the arguments row and col telling to which entity in the result set the view is applied. We can then get this entity from the result set (self.cw_rset) by using the get_entity method.

• To ease thing, we access our entity’s attribute to display using its printable_value method, which will handle formatting and escaping when necessary. As you can see, you can also access attributes by their name on the entity to get the raw value.

You can now reload the page of the community we just created and see the changes.

We have seen here a lot of thing you will have to deal with to write views in CubicWeb. The good news is that this is almost everything that is used to build higher level layers.

Note

As things get complicated and the volume of code in your cube increases, you can of course still split your views module into a python package with subpackages.

You can find more details about views and selectors in Principles.

Write entities to add logic in your data

CubicWeb provides an ORM (Object-Relational Mapper) to programmatically manipulate entities (just like the one we have fetched earlier by calling get_entity on a result set). By default, entity types are instances of the AnyEntity class, which holds a set of predefined methods as well as properties automatically generated for attributes/relations of the type it represents.

You can redefine each entity to provide additional methods or whatever you want to help you write your application. Customizing an entity requires that your entity:

• inherits from cubicweb.entities.AnyEntity or any subclass

• defines a __regid__ linked to the corresponding data type of your schema

You may then want to add your own methods, override default implementation of some method, etc… To do so, write this code in mycube/entities.py:

from cubicweb.entities import AnyEntity, fetch_config


class Community(AnyEntity):
    """customized class for Community entities"""
    __regid__ = 'Community'

    fetch_attrs, cw_fetch_order = fetch_config(['name'])

    def dc_title(self):
        return self.name

    def display_cw_logo(self):
        return 'CubicWeb' in self.name

In this example:

• we used the fetch_config() convenience function to tell which attributes should be prefetched by the ORM when looking for some related entities of this type, and how they should be ordered

• we overrode the standard dc_title() method, used in various place in the interface to display the entity (though in this case the default implementation would have had the same result)

• we implemented here a method display_cw_logo() which tests if the community title contains CubicWeb. It can then be used when you are writing code involving Community entities in your views, hooks, etc. For instance, you can modify your previous views as follows:

class CommunityPrimaryView(primary.PrimaryView):
    __select__ = is_instance('Community')

    def cell_call(self, row, col):
        entity = self.cw_rset.get_entity(row, col)
        self.w(u'<h1>Welcome to the "%s" community</h1>' % entity.printable_value('name'))

        if entity.display_cw_logo():
            self.w(u'<img src="https://docs.cubicweb.org/_static/logo-cubicweb.svg"/>')

        if entity.description:
            self.w(u'<p>%s</p>' % entity.printable_value('description'))

Then each community whose description contains ‘CW’ is shown with the CubicWeb logo in front of it.

Note

As for view, you don’t have to restart your instance when modifying some entity classes while your server is running in debug mode, the code will be automatically reloaded.

Extending the application by using more cubes!

One of the goals of the CubicWeb framework is to have truly reusable components. To do so they must behave nicely when plugged into the application and be easily customisable, from the data model to the user interface. Thanks to systems such as the selection mechanism and the choice to write views as python code, we can build our pages using true object oriented programming techniques to achieve this goal.

A library of standard cubes is available at the CubicWeb Forge to address a lot of common problems such as manipulating files, people, todos, etc. In our community blog case, we could be interested for instance in functionalities provided by the comment and tag cubes. comment provides threaded discussion functionalities and tag a simple tag mechanism to classify content. We will first modify our cube’s __pkginfo__.py file to add those cubes as dependencies:

__depends__ =  {'cubicweb': '>= 3.35.0',
                'cubicweb-blog': None,
                'cubicweb-comment': None,
                'cubicweb-tag': None}

Now we will simply tell on which entity types we want to activate the comment and tag cubes by adding respectively the comments and tags relations on them in our schema (schema.py).

class comments(RelationDefinition):
    subject = 'Comment'
    object = 'BlogEntry'
    cardinality = '1*'
    composite = 'object'


class tags(RelationDefinition):
    subject = 'Tag'
    object = ('Community', 'BlogEntry')

In the above code we activated comments on BlogEntry entities and tags on both Community and BlogEntry. Various views from both comment and tag cubes will then be automatically displayed when one of those relations is supported.

Let’s install the cubes and synchronize the data model as we’ve done earlier. So first install the cubes:

pip install cubicweb-comment cubicweb-tag

Stop the instance by pressing Ctrl-C in the terminal running the server in debug mode and enter the migration shell:

cubicweb-ctl shell myblog

Add the new cubes and exit with Ctrl-D:

add_cubes(('comment', 'tag'))

Then restart the instance with cubicweb-ctl start -D myblog and open a blog entry:

As you can see, we now have a box displaying tags and a section proposing to add a comment and displaying existing one below the post. All this without changing anything in our views, thanks to the design of generic views provided by the framework. Though if we take a look at a community, we will not see the tags box! This is because by default this box tries to locate itself in the right column within the white frame, and this column is handled by the primary view we overrode. Let’s change our view to make it more extensible, by keeping both our custom rendering but also extension points provided by the default implementation.

Add the following code in cubicweb_mycube/views.py:

class CommunityPrimaryView(primary.PrimaryView):
    __select__ = is_instance('Community')

    def render_entity_title(self, entity):
        self.w(u'<h1>Welcome to the "%s" community</h1>' % entity.printable_value('name'))

    def render_entity_attributes(self, entity):
        if entity.display_cw_logo():
            self.w(u'<img src="https://docs.cubicweb.org/_static/logo-cubicweb.svg"/>')

        if entity.description:
            self.w(u'<p>%s</p>' % entity.printable_value('description'))

By reloading the Community page, it will now appear properly:

You can control part of the interface independently from each others, piece by piece.