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+++ b/doc/book/en/annexes/faq.rst Thu May 07 16:33:22 2009 +0200
@@ -0,0 +1,244 @@
+.. -*- coding: utf-8 -*-
+
+Frequently Asked Questions
+==========================
+
+[XXX 'copy answer from forum' means reusing text from
+http://groups.google.com/group/google-appengine/browse_frm/thread/c9476925f5f66ec6
+and
+http://groups.google.com/group/google-appengine/browse_frm/thread/d791ce17e2716147/eb078f8cfe8426e0
+and
+http://groups.google.com/group/google-appengine/browse_frm/thread/f48cf6099973aef5/c28cd6934dd72457
+]
+
+* Why does not CubicWeb have a template language ?
+
+ There are enough template languages out there. You can use your
+ preferred template language if you want. [explain how to use a
+ template language]
+
+ `CubicWeb` does not define its own templating language as this was
+ not our goal. Based on our experience, we realized that
+ we could gain productivity by letting designers use design tools
+ and developpers develop without the use of the templating language
+ as an intermediary that could not be anyway efficient for both parties.
+ Python is the templating language that we use in `CubicWeb`, but again,
+ it does not prevent you from using a templating language.
+
+ The reason template languages are not used in this book is that
+ experience has proved us that using pure python was less cumbersome.
+
+* Why do you think using pure python is better than using a template language ?
+
+ Python is an Object Oriented Programming language and as such it
+ already provides a consistent and strong architecture and syntax
+ a templating language would not reach.
+
+ When doing development, you need a real language and template
+ languages are not real languages.
+
+ Using Python enables developing applications for which code is
+ easier to maintain with real functions/classes/contexts
+ without the need of learning a new dialect. By using Python,
+ we use standard OOP techniques and this is a key factor in a
+ robust application.
+
+* Why do you use the GPL license to prevent me from doing X ?
+
+ GPL means that *if* you redistribute your application, you need to
+ redistribute it *and* the changes you made *and* the code _linked_
+ to it under the GPL licence.
+
+ Publishing a web site has nothing to do with redistributing
+ source code. A fair amount of companies use modified GPL code
+ for internal use. And someone could publish a `CubicWeb` component
+ under a BSD licence for others to plug into a GPL framework without
+ any problem. The only thing we are trying to prevent here is someone
+ taking the framework and packaging it as closed source to his own
+ clients.
+
+
+* CubicWeb looks pretty recent. Is it stable ?
+
+ It is constantly evolving, piece by piece. The framework has
+ evolved over the past seven years and data has been migrated from
+ one schema to the other ever since. There is a well-defined way to
+ handle data and schema migration.
+
+* Why is the RQL query language looking similar to X ?
+
+ It may remind you of SQL but it is higher level than SQL, more like
+ SPARQL. Except that SPARQL did not exist when we started the project.
+ Having SPARQL has a query language has been in our backlog for years.
+
+ That RQL language is what is going to make a difference with django-
+ like frameworks for several reasons.
+
+ 1. accessing data is *much* easier with it. One can write complex
+ queries with RQL that would be tedious to define and hard to maintain
+ using an object/filter suite of method calls.
+
+ 2. it offers an abstraction layer allowing your applications to run
+ on multiple back-ends. That means not only various SQL backends
+ (postgresql, sqlite, mysql), but also multiple databases at the
+ same time, and also non-SQL data stores like LDAP directories and
+ subversion/mercurial repositories (see the `vcsfile`
+ component). Google App Engine is yet another supported target for
+ RQL.
+
+[copy answer from forum, explain why similar to sparql and why better
+ than django and SQL]
+
+* which ajax library
+
+ [we use jquery and things on top of that]
+
+* `Error while publishing rest text ...`
+
+ While modifying the description of an entity, you get an error message in
+ the application `Error while publishing ...` for Rest text and plain text.
+ The server returns a traceback like as follows ::
+
+ 2008-10-06 15:05:08 - (cubicweb.rest) ERROR: error while publishing ReST text
+ Traceback (most recent call last):
+ File "/home/user/src/blogdemo/cubicweb/common/rest.py", line 217, in rest_publish
+ File "/usr/lib/python2.5/codecs.py", line 817, in open
+ file = __builtin__.open(filename, mode, buffering)
+ TypeError: __init__() takes at most 3 arguments (4 given)
+
+
+ This can be fixed by applying the patch described in :
+ http://code.google.com/p/googleappengine/issues/detail?id=48
+
+* What are hooks used for?
+
+ Hooks are executed around (actually before or after) events. The
+ most common events are data creation, update and deletion. They
+ permit additional constraint checking (those not expressible at the
+ schema level), pre and post computations depending on data
+ movements.
+
+ As such, they are a vital part of the framework.
+
+ Other kinds of hooks, called Operations, are available
+ for execution just before commit.
+
+* When should you define an HTML template rather than define a graphical component?
+
+ An HTML template cannot contain code, hence it is only about static
+ content. A component is made of code and operations that apply on a
+ well defined context (request, result set). It enables much more
+ dynamic views.
+
+* What is the difference between `AppRsetObject` and `AppObject` ?
+
+ `AppRsetObject` instances are selected on a request and a result
+ set. `AppObject` instances are directly selected by id.
+
+* How to update a database after a schema modification?
+
+ It depends on what has been modified in the schema.
+
+ * Update of an attribute permissions and properties:
+ ``synchronize_eschema('MyEntity')``.
+
+ * Update of a relation permissions and properties:
+ ``synchronize_rschema('MyRelation')``.
+
+ * Add an attribute: ``add_attribute('MyEntityType', 'myattr')``.
+
+ * Add a relation: ``add_relation_definition('SubjRelation', 'MyRelation', 'ObjRelation')``.
+
+
+* How to create an anonymous user?
+
+ This allows to bypass authentication for your site. In the
+ ``all-in-one.conf`` file of your instance, define the anonymous user
+ as follows ::
+
+ # login of the CubicWeb user account to use for anonymous user (if you want to
+ # allow anonymous)
+ anonymous-user=anon
+
+ # password of the CubicWeb user account matching login
+ anonymous-password=anon
+
+ You also must ensure that this `anon` user is a registered user of
+ the DB backend. If not, you can create through the administation
+ interface of your instance by adding a user with the role `guests`.
+ This could be the admin account (for development
+ purposes, of course).
+
+.. note::
+ While creating a new instance, you can decide to allow access
+ to anonymous user, which will automatically execute what is
+ decribed above.
+
+
+* How to change the application logo?
+
+ There are two ways of changing the logo.
+
+ 1. The easiest way to use a different logo is to replace the existing
+ ``logo.png`` in ``myapp/data`` by your prefered icon and refresh.
+ By default all application will look for a ``logo.png`` to be
+ rendered in the logo section.
+
+ .. image:: ../images/lax-book.06-main-template-logo.en.png
+
+ 2. In your cube directory, you can specify which file to use for the logo.
+ This is configurable in ``mycube/data/external_resources``: ::
+
+ LOGO = DATADIR/path/to/mylogo.gif
+
+ where DATADIR is ``mycubes/data``.
+
+* How to configure LDAP source?
+
+ Your instance's sources are defined in ``/etc/cubicweb.d/myapp/sources``.
+ Configuring an LDAP source is about declaring that source in your
+ instance configuration file such as: ::
+
+ [ldapuser]
+ adapter=ldapuser
+ # ldap host
+ host=myhost
+ # base DN to lookup for usres
+ user-base-dn=ou=People,dc=mydomain,dc=fr
+ # user search scope
+ user-scope=ONELEVEL
+ # classes of user
+ user-classes=top,posixAccount
+ # attribute used as login on authentication
+ user-login-attr=uid
+ # name of a group in which ldap users will be by default
+ user-default-group=users
+ # map from ldap user attributes to cubicweb attributes
+ user-attrs-map=gecos:email,uid:login
+
+ Any change applied to configuration file requires to restart your
+ application.
+
+* I get NoSelectableObject exceptions: how do I debug selectors ?
+
+ You just need to put the appropriate context manager around view/component
+ selection: ::
+
+ from cubicweb.common.selectors import traced_selection
+ with traced_selection():
+ comp = self.vreg.select_object('contentnavigation', 'wfhistory',
+ self.req, rset, context='navcontentbottom')
+
+ This will yield additional WARNINGs, like this: ::
+
+ 2009-01-09 16:43:52 - (cubicweb.selectors) WARNING: selector one_line_rset returned 0 for <class 'cubicweb.web.views.basecomponents.WFHistoryVComponent'>
+
+* How to format an entity date attribute?
+
+ If your schema has an attribute of type Date or Datetime, you might
+ want to format it. First, you should define your preferred format using
+ the site configuration panel ``http://appurl/view?vid=systemepropertiesform``
+ and then set ``ui.date`` and/or ``ui.datetime``.
+ Then in the view code, use::
+
+ self.format_date(entity.date_attribute)