Quick overview of `CubicWeb`

============================

`CubicWeb` allows us to develop web applications instances based on

one or more `cubes`.

What we call a `cube` is a model defining the data types and views. 

A `cube` is a reusable component grouped with others cubes in the file

system.

An `instance` refers to a specific installation of one or more `cubes`

 where are grouped configuration files of the final web application.

In this document, we will show you how to create a `cube` and how to use it

in an `instance` for your web application.

Create your cube

After you installed your `CubicWeb` development environment, you can start

to build your first cube: ::

This will create in ``/path/to/forest/cubes`` a directory containing: ::

Any changes applied to your data model should be done in this

directory.

Define your data schema

-----------------------

The data model or schema is hte core of your `CubicWeb` application.

This is where is defined the type of content you application will handle.

The data model is defined in the file ``schema.py`` of your cube

``blog`` such as follows.

A Blog has a title and a description. The title is a string that is

required by the class EntityType and must be less than 50 characters. 

The description is a string that is not constrained.

A BlogEntry has a title, a publish_date and a content. The title is a

string that is required and must be less than 100 characters. The

publish_date is a Date with a default value of TODAY, meaning that

when a BlogEntry is created, its publish_date will be the current day

unless it is modified. The content is a string that will be indexed in

the full-text index and has no constraint.

A BlogEntry also has a relationship ``entry_of`` that links it to a

Blog. The cardinality ``?*`` means that a BlogEntry can be part of

zero or one Blog (``?`` means `zero or one`) and that a Blog can

have any number of BlogEntry (``*`` means `any number including

zero`). For completeness, remember that ``+`` means `one or more`.

Create your instance

This command will create a directory ``~/etc/cubicweb.d/blogdemo``

which will contain all the configuration files required to start

you web application.

The instance ``blogdemo`` is based on the cube ``blog``.

Welcome in your web application

-------------------------------

Run your application with the following command: ::

You can now access to your web application to create blogs and post messages

by visitin the URL http://localhost:8080/.

A login form will first be prompted. By default, the application will not allow

anonymous user to get in the application. You should then use the admin

account you created at the time you initialized the database with

Once authenticated, you can start playing with your application 

and create entities. Bravo!

Please notice that so far, `CubicWeb` franework managed all aspects of 

the web application based in the schema provided at first.

Create entities

---------------

We will now create a couple of entities in our web application.

Create a Blog

Let us create a few of these entities. Click on the `[+]` at the right

of the link Blog.  Call this new Blog ``Tech-blog`` and type in

``everything about technology`` as the description, then validate the

form by clicking on ``Validate``.

Click on the logo at top left to get back to the home page, then

follow the Blog link that will list for you all the existing Blog.

You should be seeing a list with a single item ``Tech-blog`` you

just created.

Clicking on this item will get you to its detailed description except

that in this case, there is not much to display besides the name and

the phrase ``everything about technology``.

Now get back to the home page by clicking on the top-left logo, then

create a new Blog called ``MyLife`` and get back to the home page

again to follow the Blog link for the second time. The list now

has two items.

Create a BlogEntry

~~~~~~~~~~~~~~~~~~

Get back to the home page and click on [+] at the right of the link

BlogEntry. Call this new entry ``Hello World`` and type in some text

before clicking on ``Validate``. You added a new blog entry without

saying to what blog it belongs. There is a box on the left entitled

``actions``, click on the menu item ``modify``. You are back to the form

to edit the blog entry you just created, except that the form now has

another section with a combobox titled ``add relation``. Chose

``entry_of`` in this menu and a second combobox appears where you pick

``MyLife``. 

You could also have, at the time you started to fill the form for a

new entity BlogEntry, hit ``Apply`` instead of ``Validate`` and the 

combobox titled ``add relation`` would have showed up.

Validate the changes by clicking ``Validate``. The entity BlogEntry

that is displayed now includes a link to the entity Blog named

``MyLife``.

Please notice that so far, `CubicWeb` franework managed all aspects of 

the web application based in the schema provided at first.

Also if you wish to get a graphical view of the schema, visit

the link `Application schema`` which will direct you to :

Define your entities views

--------------------------

The views selection principle

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A view is defined by a Python class which includes: 

  - an identifier (all objects in `CubicWeb` are entered in a registry

    and this identifier will be used as a key)

  - a filter to select the resulsets it can be applied to

`CubicWeb` provides a lot of standard views for the type

`EntityView`, for a complete list, you

will have to read the code in directory ``cubicweb/web/views/``

A view is applied on a `result set` which contains a set of

entities we are trying to display. `CubicWeb` uses a selector

mecanism which computes a score used to identify which view

is the best to apply for the `result set` we are trying to 

display. The standard library of selectors is in 

``cubicweb.common.selector`` and a library of methods used to

compute scores is available in ``cubicweb.vregistry.vreq``.

It is possible to define multiple views for the same identifier

and to associate selectors and filters to allow the application

to find the best way to render the data. We will see more details

on this in :ref:`DefinitionVues`.

For example, the view named ``primary`` is the one used to display

a single entity. We will now show you hos to customize this view.

View customization

~~~~~~~~~~~~~~~~~~

If you wish to modify the way a `BlogEntry` is rendered, you will have to 

overwrite the `primary` view defined in the module ``views`` of the cube

``cubes/blog/views.py``.

We can by example add in front of the pulication date a prefix specifying

the date we see is the publication date.

To do so, please apply the following changes:

  When a view is modified, it is not required to restart the application

  server. Save the Python file and reload the page in your web browser

  to view the changes.

You can now see that the publication date has a prefix.

The above source code defines a new primary view for

``BlogEntry``. 

Since views are applied to resultsets and resulsets can be tables of

data, it is needed to recover the entity from its (row,col)

coordinates. We will get to this in more detail later.

The view has a ``self.w()`` method that is used to output data. In our

example we use it to output HTML tags and values of the entity's attributes.