subscribe to this blog

CubicWeb Blog

News about the framework and its uses.

HOWTO change the value of a variable in all-in-one.conf with a migration script


Here is a sample migration script (see also the cubicweb documentation on that topic) which changes the variable 'sender-addr'. There is an additional twist in that the variable is only updated if the instance is configured with a known value for that variable.

wrong_addr = '' # known wrong address
fixed_addr = ''
configured_addr = config.get('sender-addr')
# check that the address has not been hand fixed by a sysadmin
if configured_addr == wrong_addr:
    config['sender-addr'] = fixed-addr

This is very useful in cases such as:

  • automatically changing the value of a variable which used a default value set by cubicweb-ctl create
  • changing the configuration of an instance with limited intervention from the local sysadmin (because asking him to hand edit the config file is error prone): he just has to deploy the new release and run cubicweb-ctl upgrade
  • fixing issues caused by settings in the all-in-one.conf file (e.g. changing the value of max-post-length)

OSCON 2010 - Data freedom and the semantic web

2010/07/29 by Sandrine Ribeau

I presented CubicWeb at OSCON 2010. I could only stay for a day and I did not get a chance to see a lot of talks, but judging from the conference schedule it seems only a few of them were related to making data available on the web. I will focus on these talks, for they are very relevant to us who are building the semantic web.

I highly encourage you to watch this video of Stormy Peters, "Is Your Data Free?". It addresses the issue of the privacy of data that you think belongs to you but actually doesn't. This is exactly what is behind the CubicWeb design: build your own web of data in a permission based environment in order to preserve your privacy.

Open source, Open data presented by the Freebase folk, makes a very interesting parallel between open source and open data raising the problematic of versioning open data and providing quality data. There are methodologies and tools for open source software to ensure well designed and reliable code. There is absolutely nothing so far that could handle properly data versioning and data quality assurance. That is the biggest concern freebase has and through this talk they asked for help from the open source community so that more people would get involved in finding solutions to serve open data.

An attendee raised an interesting question about the format that everybody would agree to use to represent the data. I was surprised by the answer. It seems that so far they do not believe that this is a concern, not to say they don't care, but almost. For freebase, the main concern and most challenging part of the data representation is to have a unique identifier. I am not quite sure I agree on that part. Yes, this is important, even mandatory, but there is also the need to define or use a known format to represent this data, (RDF for example) so that we can source this data. To be semantic data, it needs to be both identifiable and readable. And I do not see the point of publishing data on the web if it is not ready to use.

Just for fun, look at Rewrite or Refactor: When to Declare Technical Bankruptcy, it might sounds familiar to you...

CubicWeb presentation went well, an interested audience which was very happy to see that we could aggregate multiple types of sources in a CubicWeb application. Of course, it would be even better if we would support an RDF source such as dbpedia: don't worry that's going to happen. Also what raised an interest is the semantic views already integrated in the framework such as SIOC, OWL, FOAF, DOAP that you can find in blog entries (sioc), schema (owl), user (foaf), project (doap).


RDF Resource Description Framework Icon OWL Button - microformats JSON - RSS dublincore DOAP SIOC - FOAF


By providing a platform for using data from multiple sources and publishing semantic data, CubicWeb is already a piece of the web of open data!

Building my photos web site with CubicWeb part IV: let's make it more user friendly

2010/07/13 by Sylvain Thenault

Step 0: updating code to CubicWeb 3.9 / cubicweb-file 1.9

CubicWeb 3.9 brings several improvements that we'll want to use, and the 1.9 version of the file cube has a major change: the Image type has been dropped in favor of an IImage adapter that makes code globally much cleaner (although this is not directly visible here). So the first thing to do is to upgrade our cube to the 3.9 API. As CubicWeb releases are mostly backward compatible, this is not mandatory but it's easier to follow changes as they come than having a huge upgrade to do at some point. Also, this remove deprecation warnings which are a bit tedious...

Since we only have very few lines of code, this step is pretty simple. Actually the main thing we have to do is to upgrade our schema, to remove occurrences of the Image type or replace them by the File type. Here is the (striped) diff:

 class comments(RelationDefinition):
     subject = 'Comment'
-    object = ('File', 'Image')
+    object = 'File'
     cardinality = '1*'
     composite = 'object'

 class tags(RelationDefinition):
     subject = 'Tag'
-    object = ('File', 'Image')
+    object = 'File'

 class displayed_on(RelationDefinition):
     subject = 'Person'
-    object = 'Image'
+    object = 'File'

 class situated_in(RelationDefinition):
-    subject = 'Image'
+    subject = 'File'
     object = 'Zone'

 class filed_under(RelationDefinition):
-    subject = ('File', 'Image')
+    subject = 'File'
     object = 'Folder'

 class visibility(RelationDefinition):
-    subject = ('Folder', 'File', 'Image', 'Comment')
+    subject = ('Folder', 'File', 'Comment')
     object = 'String'
     constraints = [StaticVocabularyConstraint(('public', 'authenticated',
                                                'restricted', 'parent'))]

 class may_be_readen_by(RelationDefinition):
-    subject = ('Folder', 'File', 'Image', 'Comment',)
+    subject = ('Folder', 'File', 'Comment',)
     object = 'CWUser'

-from cubes.file.schema import File, Image
+from cubes.file.schema import File

 File.__permissions__ = VISIBILITY_PERMISSIONS
-Image.__permissions__ = VISIBILITY_PERMISSIONS

Now, let's set the dependency in the __pkginfo__ file. As 3.8 simplifies this file, we can merge __depends_cubes__ (as introduced in the first blog of this series) with __depends__ to get the following result:

__depends__ = {'cubicweb': '>= 3.9.0',
               'cubicweb-file': '>= 1.9.0',
               'cubicweb-folder': None,
               'cubicweb-person': None,
               'cubicweb-zone': None,
               'cubicweb-comment': None,
               'cubicweb-tag': None,

If your cube is packaged for debian, it's a good idea to update the debian/control file at the same time, so you won't forget it.

That's it for the API update, CubicWeb and cubicweb-file will handle other stuff for us. Easy, no?

We can now start some more fun stuff...

Step 1: let's improve site's usability for our visitors

The first thing I've noticed is that people to whom I send links to photos with some login/password authentication get lost, because they don't grasp they have to login by clicking on the 'authenticate' link. That's probably because they only get a 404 when trying to access an unauthorized folder, and the site doesn't make clear that 1. you're not authenticated, 2. you could get more content by authenticating yourself.

So, to improve this situation, I decided that I should:

  • make a login box appears for anonymous, so they see at a first glance a place to put the login / password information I provided
  • customize the 404 page, proposing to login to anonymous.

Here is the code, samples from my cube's file:

from cubicweb.selectors import is_instance
from cubicweb.web import box
from cubicweb.web.views import basetemplates, error

class FourOhFour(error.FourOhFour):
    __select__ = error.FourOhFour.__select__ & anonymous_user()

    def call(self):
        self.w(u"<h1>%s</h1>" % self._cw._('this resource does not exist'))
        self.w(u"<p>%s</p>" % self._cw._('have you tried to login?'))

class LoginBox(box.BoxTemplate, basetemplates.LogFormView):
    """display a box containing links to all startup views"""
    __regid__ = 'sytweb.loginbox'
    __select__ = box.BoxTemplate.__select__ & anonymous_user()

    title = _('Authenticate yourself')
    order = 70

    def call(self, **kwargs):
        self.w(u'<div class="sideBoxTitle"><span>%s</span></div>' % self.title)
        self.w(u'<div class="sideBox"><div class="sideBoxBody">')

The first class provides a new specific implementation of the default page you get on a 404 error, to display an explicit message for anonymous users.


Thanks to the selection mechanism, it will be selected for anonymous users, since the additional anonymous_user() selector gives it a higher score than the default, and not for authenticated since this selector will return 0 otherwise (hence the object won't be selectable).

The second class defines a simple box, that will be displayed by default with boxes in the left column, thanks to default box.BoxTemplate'selector. The HTML is written to match default CubicWeb boxes style. To get the actual login form, we inherit from the LogFormView view which provides a login_form method (handling some stuff under the cover for us, hence the multiple inheritance), that we simply have to call to get the form's HTML.

login box / 404 screenshot

The login box and the custom 404 page for an anonymous visitor (translated in french)

Step 2: providing a custom index page

Another thing we can easily do to improve the site is... A nicer index page (e.g. the first page you get when accessing the web site)! The default one is quite intimidating (that should change in a near future). I will provide a much simpler index page that simply list available folders (e.g. photo albums in that site).

from cubicweb.web.views import startup

class IndexView(startup.IndexView):
    def call(self, **kwargs):
        if self._cw.cnx.anonymous_connection:
            self.w(u'<h4>%s</h4>\n' % self._cw._('Public Albums'))
            self.w(u'<h4>%s</h4>\n' % self._cw._('Albums for %s') % self._cw.user.login)
        self._cw.vreg['views'].select('tree', self._cw).render(w=self.w)

def registration_callback(vreg):
    vreg.register_all(globals().values(), __name__, (IndexView,))
    vreg.register_and_replace(IndexView, startup.IndexView)

As you can see, we override the default index view found in cubicweb.web.views.startup, getting back nothing but its identifier and selector since we override the top level view's call method.


In that case, we want our index view to replace the existing one. We implement the registration_callback function, in which we code a registeration of everything in the module but our IndexView, then we register it instead of the former index view.

Also, we added a title that tries to make it more evident that the visitor is authenticated, or not. Hopefully people will get it now!

default index page screenshot

The default index page

new index page screenshot

Our simpler, less intimidating, index page (still translated in french)

Step 3: more navigation improvements

There are still a few problems I want to solve...

  • Images in a folder are displayed in a somewhat random order. I would like to have them ordered by file's name (which will usually, inside a given folder, also result ordering photo by their date and time)
  • When clicking a photo from an album view, you've to get back to the gallery view to go to the next photo. This is pretty annoying...
  • Also, when viewing an image, there is no clue about the folder to which this image belongs to.

I will first try to explain the ordering problem. By default, when accessing related entities by using the ORM's API, you should get them ordered according to the target's class fetch_order. If we take a look at the file cube's schema, we can see:

class File(AnyEntity):
    """customized class for File entities"""
    __regid__ = 'File'
    fetch_attrs, fetch_order = fetch_config(['data_name', 'title'])

By default, fetch_config will return a fetch_order method that will order on the first attribute in the list. We could expect to get files ordered by their name. But we don't. What's up doc ?

The problem is that files are related to folder using the filed_under relation. And that relation is ambiguous, eg it can lead to File entities, but also to Folder entities. In such a case, since both entity types don't share the attribute on which we want to sort, we'll get linked entities sorted on a common attribute (usually modification_date).

To fix this, we have to help the ORM. We'll do this in the method from the ITree folder's adapter, used in the folder's primary view to display the folder's content. Here's the code that I've put in our cube's file, since it's more logical stuff than view stuff:

from cubes.folder import entities as folder

class FolderITreeAdapter(folder.FolderITreeAdapter):

    def different_type_children(self, entities=True):
        rql = self.entity.cw_related_rql(self.tree_relation,
                                         self.parent_role, ('File',))
        rset = self._cw.execute(rql, {'x': self.entity.eid})
        if entities:
            return list(rset.entities())
        return rset

def registration_callback(vreg):
    vreg.register_and_replace(FolderITreeAdapter, folder.FolderITreeAdapter)

As you can see, we simply inherit from the adapter defined in the folder cube, then we override the different_type_children method to give a clue to the ORM's cw_related_rql method, that will generate the rql to get entities related to the folder by the filed_under relation (the value of the tree_relation attribute). The clue is that we only want to consider the File target entity type. By doing this, we remove the ambiguity and get back a RQL query that correctly orders files by their data_name attribute.


  • Adapters have been introduced in CubicWeb 3.9 / cubicweb-folder 1.8.
  • As seen earlier, we want to replace the folder's ITree adapter by our implementation, hence the custom registration_callback method.

Ouf. That one was tricky...

Now the easier parts. Let's start by adding some links on the file's primary view to see the previous / next image in the same folder. CubicWeb provides a component that do exactly that. To make it appear, it has to be adaptable to the IPrevNext interface. Here is the related code sample, extracted from our cube's file:

from cubicweb.selectors import is_instance
from cubicweb.web.views import navigation

class FileIPrevNextAdapter(navigation.IPrevNextAdapter):
    __select__ = is_instance('File')

    def previous_entity(self):
        rset = self._cw.execute('File F ORDERBY FDN DESC LIMIT 1 WHERE '
                                'X filed_under FOLDER, F filed_under FOLDER, '
                                'F data_name FDN, X data_name > FDN, X eid %(x)s',
                                {'x': self.entity.eid})
        if rset:
            return rset.get_entity(0, 0)

    def next_entity(self):
        rset = self._cw.execute('File F ORDERBY FDN ASC LIMIT 1 WHERE '
                                'X filed_under FOLDER, F filed_under FOLDER, '
                                'F data_name FDN, X data_name < FDN, X eid %(x)s',
                                {'x': self.entity.eid})
        if rset:
            return rset.get_entity(0, 0)

The IPrevNext interface implemented by the adapter simply consist of the previous_entity / next_entity methods, that should respectively return the previous / next entity or None. We make an RQL query to get files in the same folder, ordered similarly (eg by their data_name attribute). We set ascendant/descendant ordering and a strict comparison with current file's name (the "X" variable representing the current file).


  • Former implements selector should be replaced by is_instance or adaptable selector with CubicWeb >= 3.9. In our case, is_instance is used to tell our adapter to get File entities.

Notice that this query supposes we wont have two files of the same name in the same folder. Fixing this is out of the scope of this blog. And as I would like to have at some point a smarter, context sensitive previous/next entity, I'll probably never fix this query (though if I had to, I would probably choose to add a constraint in the schema so that we can't add two files of the same name in a folder).

One more thing: by default, the component will be displayed below the content zone (the one with the white background). You can change this in the site's properties through the ui, but you can also change the default value in the code by modifying the context attribute of the component:

navigation.NextPrevNavigationComponent.context = 'navcontentbottom'


context may be one of 'navtop', 'navbottom', 'navcontenttop' or 'navcontentbottom'; the first two being outside the main content zone, the two others inside it.

screenshot of the previous/next entity component

The previous/next entity component, at the bottom of the main content zone.

Now, the only remaining stuff in my todo list is to see the file's folder. I'll use the standard breadcrumb component to do so. Similarly as what we've seen before, this component is controlled by the IBreadCrumbs interface, so we'll have to provide a custom adapter for File entity, telling the a file's parent entity is its folder:

from cubicweb.web.views import ibreadcrumbs

class FileIBreadCrumbsAdapter(ibreadcrumbs.IBreadCrumbsAdapter):
    __select__ = is_instance('File')

    def parent_entity(self):
        if self.entity.filed_under:
            return self.entity.filed_under[0]

In this case, we simply use the attribute notation provided by the ORM to get the folder in which the current file (e.g. self.entity) is located.


The IBreadCrumbs interface is a breadcrumbs method, but the default IBreadCrumbsAdapter provides a default implementation for it that will look at the value returned by its parent_entity method. It also provides a default implementation for this method for entities adapting to the ITree interface, but as our File doesn't, we've to provide a custom adapter.

screenshot of the breadcrumb component

The breadcrumb component when on a file entity, now displaying parent folder.

Step 4: preparing the release and migrating the instance

Now that greatly enhanced our cube, it's time to release it and to upgrade production site. I'll probably detail that process later, but I currently simply transfer the new code to the server running the web site.

However, there's some commands to get things done properly... First, as I've added some translatable string, I have to run:

$ cubicweb-ctl i18ncube sytweb

To update the cube's gettext catalogs (the '.po' files under the cube's i18n directory). Once the above command is executed, I'll then update translations.

To see if everything is ok on my test instance, I do:

$ cubicweb-ctl i18ninstance sytweb
$ cubicweb-ctl start -D sytweb

The first command compile i18n catalogs (e.g. generates '.mo' files) for my test instance. The second command starts it in debug mode, so I can open my browser and navigate through the web site to see if everything is ok...


In the 'cubicweb-ctl i18ncube' command, sytweb refers to the cube, while in the two other, it refers to the instance (if you can't see the difference, reread CubicWeb's concept chapter !).

Once I've checked it's ok, I simply have to bump the version number in the __pkginfo__ module to trigger a migration once I'll have updated the code on the production site. I can check the migration is also going fine, by first restoring a dump from the production site, then upgrading my test instance.

To generate a dump from the production site:

$ cubicweb-ctl db-dump sytweb
pg_dump -Fc --username=syt --no-owner --file /home/syt/etc/cubicweb.d/sytweb/backup/tmpYIN0YI/system sytweb
-> backup file /home/syt/etc/cubicweb.d/sytweb/backup/sytweb-2010-07-13_10-22-40.tar.gz

I can now get back the dump file ('sytweb-2010-07-13_10-22-40.tar.gz') to my test machine (using scp for instance) to restore it and start migration:

$ cubicweb-ctl db-restore sytweb sytweb-2010-07-13_10-22-40.tar.gz
$ cubicweb-ctl upgrade sytweb

You'll have to answer some questions, as we've seen in an earlier post.

Now that everything is tested, I can transfer the new code to the production server, apt-get upgrade cubicweb 3.9 and its dependencies, and eventually upgrade the production instance.


This is a somewhat long post that starts showing you the way CubicWeb provides a highly configurable user interface, as well as powerful and reusable components. And there are a lot of others like those!

So see you next time for part V, where we'll probably want to do more ui stuff!

CubicWeb 3.9 released

2010/07/12 by Sylvain Thenault

CubicWeb 3.9.0 went out last week. We now have tested it in production and fixed the remaining bugs, which means it is now show time!

What's new in CubicWeb 3.9?

The 3.9 release development was started by a one week long sprint at the beginning of May. The two goals were first to make it easier to customize the look and feel of a CubicWeb application, and second to do a big cleanup of the javascript library. This led to the following major changes.

  • We introduced property sheets, which replace former external_resources file, as well as define some constants that will be used to 'compile' cubicweb and cubes' stylesheets.
  • We started a new, clean cubicweb.css stylesheet, that tries to keep up with the rhythm. This is still a work in progress, and by default the old css is still used, unless specified otherwise in the configuration file.
  • We set the bases for web functional testing using windmill. See test cases in cubicweb/web/test/windmill/ and python wrapper in cubicweb/web/test_windmill/ if you want to use this in your own cube.
  • We set the bases for javascript unit-testing using qunit. See test cases in cubicweb/web/test/jstests/ and python wrapper in cubicweb/web/test_jscript/ if you want to use this in your own cube.
  • We cleaned the javascript code: the generic stuff moved into the cw namespace, the ajax api is now much simpler thanks to more generic and powerful functions. As usual backward compatibility was kept, which means that your existing code will still run, but you will see tons of deprecation warnings in the firebug console.
  • We implemented a simple documentation extraction system for javascript. Just put ReST in javascript comments, and get all the power of sphinx for documenting your javascript code.

But that's not all! There are also two major changes in 3.9.

Architectural change: adapters

The first major change is the introduction of adapters, also found in the Zope Component Architecture and documented in the GoF book. This will allow for better application design and easier code reuse. You can see several usage in the framework, for instance the "ITree" adapter in cubicweb.entities.adapters, the "IBreadCrumbs" adapter in cubicweb.web.views.ibreadcrumbs, or still the "ICalendarable" adapter in cubicweb.web.views.calendar.

Important full search improvement

The second major change will benefit directly to end users: we worked with our friends from SecondWeb to expose the ranking feature found in postgres full-text search. This clearly improves the user experience when doing full-text searches. Ranking may be finely tuned by setting different weights to entity types, entity types attributes, or even be dynamically computed per entity instance. Of course, all this is done in an adapter, see "IFTIndexableAdapter" in cubicweb/entities/

Minor changes

Other minor changes include:

  • support for wildcard text search for application using postgres >= 8.4 as backend. Try searching for 'cub*' on for instance.
  • inline edition of composite relation
  • nicer, clickable, schema image of the data model
  • enhanced support for the SQLserver database


Using RQL's HAVING clause to by-pass limitation of the WHERE clause

2010/06/09 by Sylvain Thenault

The HAVING clause, as in SQL, has been originally introduced to restrict a query according to value returned by an aggregat function, e.g.:


It may however be used for something else...

For instance, let's say you want to get people whose uppercased first name equals to another person uppercased first name. Since in the WHERE clause, we are limited to 3-expression (<subject> <relation> <object>), such thing can't be expressed (believe me or try it out). But this can be expressed using HAVING comparison expression:

Person X WHERE X firstname XFN, Y firstname YFN HAVING X > Y, UPPER(XFN) = UPPER(YFN)

Nice, no? This open some new possibilities. Another example:

Person X WHERE X birthday XB HAVING YEAR(XB) = 2000

Get it? That lets you use transformation functions not only in selection but for restriction as well, which was the major flaw in the RQL language.

Notice that while we would like this to work without the HAVING clause, this can't be currently be done because it introduces an ambiguity in RQL's grammar that can't be handled by yapps, the parser's generator we're using.

Deactivating the 'reledit' feature

2010/06/09 by Sylvain Thenault

The 'reledit' feature is the one that makes attributes/relations editable in entity's primary view for authorized users (you know, the pen that appears when your mouse is over a field's value, clicking on it making a form to edit this field appears).

This is a nice feature, but you may not want it. It can be easily deactivated everywhere it's used automatically in the site by using the code snippet below:

from cubicweb.web.views import editforms

class DeactivatedAutoClickAndEditFormView(editforms.AutoClickAndEditFormView):
    def should_edit_attribute(self, entity, rschema, form):
        return False

    def should_edit_relation(self, entity, rschema, role, rvid):
        return False

def registration_callback(vreg):

Django, lessons learned in the world of startup companies

2010/06/02 by Sandrine Ribeau

I went to the BayPIGgies meeting last thursday. The talk of this session was led by the chief software architect of RubberCan, Barnaby Bienkowski. The idea was to explain why Django turns out to be the choice a lot of startups make when building their web applications.

Governement 2.0

The fact that Django is recommended by Sunlight Foundation is important. This foundation is a non-partisan, non-profit organization based in Washington, DC that focuses on the digitization of government data and the creation of tools and Web sites to make that data easily accessible for all citizens. This is part of what is called Governement 2.0. It is a neologism for attempts to apply the social networking and integration advantages of Web 2.0 to the practice of government (see E-Governement).

It looks like the Sunlight Foundation recommends Django because it comes from the publishing industry. I am not sure what is so special about this, but I wish I could get more details on it, so please add your comments below.

Since the CubicWeb's community is still small, we are not yet recommended by such a large foundation, but we'll make more effort to talk about it and try to expand our community.


These days, geo-localization is a big deal in most applications. On that matter, what Django has to offer is GeoDjango, that recently became part of the Django core. It is integrated with the ORM and has pre-generated SQL queries, but it is not optimized. It uses PostGIS, which adds support for geographic objects to the PostgreSQL object-relational database. GeoDjango strives to make it as simple as possible to create geographic web applications, like location-based services. Some of the features it provides are:

  • Extensions to Django’s ORM for the querying and manipulation of spatial data
  • Editing of geometry fields inside the administration panels
  • Loosely-coupled, high-level Python interfaces for GIS geometry operations and data formats.

OpenStreetMap is used for the backend. It provides geographic data for any part of the world. This is a nice feature and we should consider it for CubicWeb. What we provide so far is an interface IGeocodable with related views gmap-view, gmap-bubble, geocoding-json and gmap-legend. We do not query this data yet, we simply render them nicely in a Google Map. You can find the details on how to use it here.

Online stores

Numerous web applications are not only service or data providers, they sell something. Satchmo is the Django tool to easily build online stores. It provides a shopping cart framework with checkout using different payment modules such as, TrustCommerce, CyberSource, PayPal, Google Checkout or Protx.

CubicWeb does not provide a component allowing to build an online store, it's not yet a domain we worked on. But I'd like to talk a bit about the cube cubicweb-shoppingcart. This cube defines shopping item and shopping cart, and enables to add items to the shopping cart. It defines type of shopping items and only those can be added to the shopping cart. Whereas Satchmo required to define categories and add items within a category, cubicweb-shoppingcart does not oblige to define categories. Creating shopping items is the only thing you need to do. That makes this component usable not only for online store. For example, we used this cube to manage Euroscipy registration fees reusing the generic schema of a "virtual" shopping cart and its related ressources (web widgets, validation hook, ...).

Re-usable components

Pinax has a overall good satisfaction as it supports basics components for blogging, tagging, registration, notification and so on. But one point that was raised, is the difficulty of customizing Pinax components. It seems easy to write your own version of Pinax components, but to integrate them is a pain. All the components are tightly related and by customizing one, there is a big chance it will affect the other components.

This last point is a big disadvantage. Why? Well, as a developer there is always something that you need to adjust to fit your needs. So customizing components is something you will not avoid while developing your web application. And something I'd like to point about CubicWeb, is its simplicity of re-using existing components, which are independent from each others. This is as easy as Python inheritance. And with its VRegistry, selectors and application objects (see The VRegistry, selectors and application objects for more details), customization is well integrated into the framework.

Assemble cubes and functionalities is very easy as well. Let's think of an example. We have those three cubes: cubicweb-book, cubicweb-tag and cubicweb-comment. Cubicweb-book defines Book entity type. Cubicweb-tag defines Tag entities and the ability to tag other entity types. Cubicweb-comment defines Comment entity type and the ability to comment other entity types. What if we want to create an application in which we could tag and comment Book. Well, this is done with the following schema definition where we explicitly define the relations between Book, Tag and Comment entity types:

from yams.buildobjs import RelationDefinition
class comments(RelationDefinition):
    subject = 'Comment'
    object = 'Book'
    cardinality = '1*'
    composite = 'subject'

class tag(RelationDefinition):
    subject = 'Tag'
    object = 'Book'
    cardinality = '**'


Despite the fact that forms are easy in Django, there is no way to add inline entities, at least for now (see this proposition) as easily as in CubicWeb (see HTML form construction for more details). That is very neat when you create/edit related entities. Plus, since CubicWeb 3.6, forms are much easier to handle, and we still put a lot of effort into making it simplier.

So, yes, overall Django is selected as the best compromise, but for the reason I listed, CubicWeb should be considered.

Watch out Django, we are getting on your way ;)

OSCON 2010 discount!!

2010/05/21 by Sandrine Ribeau

Since Logilab will be presenting CubicWeb at OSCON, we get to have a discount code giving 20% rebate on OSCON registration. Please feel free to use this discount code while registering: os10fos.

See you there!

Building my photos web site with CubicWeb part III: storing images on the file-system

2010/05/20 by Sylvain Thenault

Step 1: configuring the BytesFileSystem storage

To avoid cluttering my database, and to ease file manipulation, I don't want them to be stored in the database. I want to be able create File/Image entities for some files on the server file system, where those file will be accessed to get entities data. To do so, I've to set a custom BytesFileSystemStorage storage for the File/Image 'data' attribute, which holds the actual file's content.

Since the function to register a custom storage needs to have a repository instance as a first argument, we have to call it in a server startup hook. So I added it in cubes/sytweb/ :

from os import makedirs
from os.path import join, exists

from cubicweb.server import hook
from cubicweb.server.sources import storage

class ServerStartupHook(hook.Hook):
    __regid__ = 'sytweb.serverstartup'
    events = ('server_startup', 'server_maintenance')

    def __call__(self):
        bfssdir = join(self.repo.config.appdatahome, 'bfss')
        if not exists(bfssdir):
            print 'created', bfssdir
        storage = storages.BytesFileSystemStorage(bfssdir)
        set_attribute_storage(self.repo, 'File', 'data', storage)
        set_attribute_storage(self.repo, 'Image', 'data', storage)


  • how we built the hook's registry identifier (_regid__): you can introduce 'namespaces' by using their python module like naming identifiers. This is especially important for hooks where you usually want a new custom hook, not overriding / specializing an existent one, but the concept may be used for any application objects
  • we catch two events here: "server_startup" and "server_maintenance". The first is called on regular repository startup (eg, as a server), the other for maintenance task such as shell or upgrade. In both cases, we need to have the storage set, else we'll be in trouble...
  • the path given to the storage is the place where a file added through the ui (or in the database before migration) will be located
  • be aware that by doing this, you can't write queries that will try to restrict on the File and the Image data attribute anymore. Thankfully we don't usually do that on a file's content or more generally on attributes for the Bytes type

Now, if you've already added some photos through the web ui, you'll have to migrate existing data so that the file's content will be stored on the file-system instead of the database. There is a migration command to do so, let's run it in the cubicweb shell (in actual life, you'd have to put it in a migration script as we saw last time):

$ cubicweb-ctl shell sytweb
 entering the migration python shell
 just type migration commands or arbitrary python code and type ENTER to execute it
 type "exit" or Ctrl-D to quit the shell and resume operation
 >>> storage_changed('File', 'data')
 >>> storage_changed('Image', 'data')

That's it. Now, the files added through the web ui will have their content stored on the file-system, and you'll also be able to import files from the file-system as explained in the next part.

Step 2: importing some data into the instance

Hey, we're starting to have some nice features, let's give this new web site a try. For instance if I have a 'photos/201005WePyrenees' containing pictures for a particular event, I can import it to my web site by typing

$ cubicweb-ctl fsimport -F sytweb photos/201005WePyrenees/
** importing directory /home/syt/photos/201005WePyrenees
  importing IMG_8314.JPG
  importing IMG_8274.JPG
  importing IMG_8286.JPG
  importing IMG_8308.JPG
  importing IMG_8304.JPG


The -F option tell that folders should be mapped, hence my photos will be all under a Folder entity corresponding to the file-system folder.

Let's take a look at the web ui:

Nothing different, I can't see the new folder... But remember our security model! By default, files are only accessible to authenticated users, and I'm looking at the site as anonymous, e.g. not authenticated. If I login, I can now see:

Yeah, it's there! You can also notice that I can see some entities as well as folders and images the anonymous users can't. It just works everywhere in the ui since it's handled at the repository level, thanks to our security model.

Now if I click on the newly inserted folder, I can see

Great! I get my pictures in the folder. I can now give a nicer name to this folder (provided I don't intend to import from it anymore, else already imported photos will be reimported), change permissions, title for some pictures, etc... Having good content is much more difficult than having a good web site ;)


We started to see here an advanced feature of our repository: the ability to store some parts of our data-model into a custom storage, outside the database. There is currently only the BytesFileSystemStorage available, but you can expect to see more coming in a near future.

Also, we can now start to feed our web-site with some nice pictures! The site isn't perfect (far from it actually) but it's usable, and we can start using it and improve it on the way. The Incremental Cubic Way :)

So see you next time to start tweaking the user interface!

CSS+JS sprint report - Day 1 and 2 (April 2010)

2010/04/30 by Adrien Di Mascio

These first two days essentially consisted in exploring the javascript world.

Documenting javascript

Sandrine and Alain worked on the javascript documentation tools and how they could be integrated into our sphinx generated documentation.

They first studied pyjsdoc which unfortunately only generates HTML. After a somewhat successful attempt to generate sphinx ReST, we decided to use a consistent documentation format between python modules and js modules and therefore switched to a home-made, very simple javascript comment parser. Here's an example of what the parser understands:

 * .. cfunction:: myFunction(a, b, /*...*/, c, d)
 *    This function is very **well** documented and does quite
 *    a lot of stuff :
 *    - task 1
 *    - task 2
 *    :param a: this is the first parameter
 *    ...
 *    :return: 42
function myFunction(a, b, /*...*/, c, d) {

The extracted ReST snippets are then concatenated and inserted in the general documentation.

Unit testing javascript

Katia, Julien and Adrien looked at the different testing tools for javascript, with the two following goals in mind:

  • low-level unit testing, as cubicweb agnostic as possible
  • high-level / functional testing, we want to write navigation scenarios and replay them

And the two winners of the exploration are:
  • QUnit for pure javascript / DOM testing. Julien and Adrien successfully managed to test a few cubicweb js functions, most notably the loadxhtml jquery plugin.
  • Windmill for higher level testing. Katia and Sylvain were able to integrate Windmill within the CubicWeb unit testing framework.

Of course, there is still a lot of work that needs to be done. For instance, we would like to have a test runner facility to run QUnit-based tests on multiple platforms / browsers automatically.

Parametrized stylesheets and vertical rhythm

Sylvain worked on property sheets and managed to implement compiled CSS based on simple string interpolation. Of course, compiled CSS are still HTTP cached, automatically recompiled on debug mode, etc. On his way, he also got rid of the external_resources file. Backward compatibility will of course be guaranteed for a while.

Nicolas worked on CSS and vertical rythm and prepared a patch that introduces a basic rhythm. The tedious work will be to get every stylesheet to dance to the beat.