.. _controllers:

Controllers

-----------

Overview

++++++++

Controllers are responsible for taking action upon user requests

(loosely following the terminology of the MVC meta pattern).

The following controllers are provided out-of-the box in CubicWeb. We

`Browsing`:

  system build up the whole content; it handles ObjectNotFound and

  NoSelectableObject errors that may bubble up to its entry point, in

  an end-user-friendly way (but other programming errors will slip

  through)

`Edition`:

* the Edit controller (see :ref:`edit_controller`) handles CRUD

  operations in response to a form being submitted; it works in close

  association with the Forms, to which it delegates some of the work

`Other`:

* the SendMail controller (web/views/basecontrollers.py) is reponsible

  for outgoing email notifications

* the MailBugReport controller (web/views/basecontrollers.py) allows

  to quickly have a `repotbug` feature in one's application

Registration

++++++++++++

All controllers (should) live in the 'controllers' namespace within

the global registry.

API

+++

Most API details should be resolved by source code inspection, as the

various controllers have differing goals.

`web/controller.py` contains the top-level abstract Controller class and

its (NotImplemented) entry point `publish(rset=None)` method.

A handful of helpers are also provided there:

* process_rql builds a result set from an rql query typically issued

  from the browser (and available through _cw.form['rql'])

* validate_cache will force cache validation handling with respect to

  the HTTP Cache directives (that were typically originally issued

  from a previous server -> client response); concrete Controller

  implementations dealing with HTTP (thus, for instance, not the

  SendMail controller) may very well call this in their publication

  process.

.. _edit_controller:

The `edit controller`

+++++++++++++++++++++

It can be found in (:mod:`cubicweb.web.views.editcontroller`).

Editing control

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

  <field name>:<entity eid>

where entity eid could be a letter in case of an entity to create. We

name those parameters as *qualified*.

1. Retrieval of entities to edit by looking for the forms parameters

   starting by `eid:` and also having a parameter `__type` associated

   (also *qualified* by eid)

2. For all the attributes and the relations of an entity to edit:

   1. search for a parameter `edits-<relation name>` or `edito-<relation name>`

      qualified in the case of a relation where the entity is object

   2. if found, the value returned is considered as the initial value

      for this relaiton and we then look for the new value(s)  in the parameter

      <relation name> (qualified)

   3. if the value returned is different from the initial value, an database update

      request is done

3. For each entity to edit:

   1. if a qualified parameter `__linkto` is specified, its value has to be

      a string (or a list of string) such as: ::

        <relation type>:<eids>:<target>

      where <target> is either `subject` or `object` and each eid could be

      separated from the others by a `_`. Target specifies if the *edited entity*

      is subject or object of the relation and each relation specified will

      be inserted.

    2. if a qualified parameter `__clone_eid` is specified for an entity, the

       relations of the specified entity passed as value of this parameter are

       copied on the edited entity.

    3. if a qualified parameter `__delete` is specified, its value must be

       a string or a list of string such as follows: ::

          <ssubjects eids>:<relation type>:<objects eids>

       where each eid subject or object can be seperated from the other

       by `_`. Each relation specified will be deleted.

    4. if a qualified parameter `__insert` is specified, its value should

       follow the same pattern as `__delete`, but each relation specified is

       inserted.

4. If the parameters `__insert` and/or `__delete` are found not qualified,

   they are interpreted as explained above (independantly from the number

   of entities edited).

5. If no entity is edited but the form contains the parameters `__linkto`

   and `eid`, this one is interpreted by using the value specified for `eid`

   to designate the entity on which to add the relations.

.. note::

   * If the parameter `__action_delete` is found, all the entities specified

     as to be edited will be deleted.

   * If the parameter `__action_cancel` is found, no action is completed.

   * If the parameter `__action_apply` is found, the editing is

     applied normally but the redirection is done on the form (see

     :ref:`RedirectionControl`).

   * The parameter `__method` is also supported as for the main template

   * If no entity is found to be edited and if there is no parameter

     `__action_delete`, `__action_cancel`, `__linkto`, `__delete` or

     `__insert`, an error is raised.

   * Using the parameter `__message` in the form will allow to use its value

     as a message to provide the user once the editing is completed.

.. _RedirectionControl:

Redirection control

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

Once editing is completed, there is still an issue left: where should we go

now? If nothing is specified, the controller will do his job but it does not

mean we will be happy with the result. We can control that by using the

following parameters:

* `__redirectpath`: path of the URL (relative to the root URL of the site,

  no form parameters

* `__redirectparams`: forms parameters to add to the path

* `__redirectrql`: redirection RQL request

* `__redirectvid`: redirection view identifier

* `__errorurl`: initial form URL, used for redirecting in case a validation

  error is raised during editing. If this one is not specified, an error page

  is displayed instead of going back to the form (which is, if necessary,

  responsible for displaying the errors)

* `__form_id`: initial view form identifier, used if `__action_apply` is

  found

In general we use either `__redirectpath` and `__redirectparams` or

`__redirectrql` and `__redirectvid`.