.. _form_dissection:

Dissection of a form

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

This is done (again) with a vanilla instance of the `tracker`_

cube. We will populate the database with a bunch of entities and see

what kind of job the automatic entity form does.

.. _`tracker`: http://www.cubicweb.org/project/cubicweb-tracker

Patching the session object

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

In order to play interactively with web side application objects, we

have to cheat a bit: we will decorate the session object with some

missing artifacts that should belong to a web request object. With

that we can instantiate and render forms interactively.

The function below does the minimum to allow going through this

exercice. Some attributes or methods may be missing for other

purposes. It is nevertheless not complicated to enhance it if need

arises.

.. sourcecode:: python

 def monkey_patch_session(session):

     """ useful to use the cw shell session object

     with web appobjects, which expect more than a plain

     data repository session

     """

     # for autoform selection

     session.json_request = False

     session.url = lambda: u'http://perdu.com'

     session.session = session

     session.form = {}

     session.list_form_param = lambda *args: []

     # for render

     session.use_fckeditor = lambda: False

     session._ressources = []

     session.add_js = session.add_css = lambda *args: session._ressources.append(args)

     session.external_resource = lambda x:{}

     session._tabcount = 0

     def next_tabindex():

         session._tabcount += 1

         return session._tabcount

     session.next_tabindex = next_tabindex

     return session

Populating the database

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

We should start by setting up a bit of context: a project with two

unpublished versions, and a ticket linked to the project and the first

version.

.. sourcecode:: python

 >>> p = rql('INSERT Project P: P name "cubicweb"')

 >>> for num in ('0.1.0', '0.2.0'):

 ...  rql('INSERT Version V: V num "%s", V version_of P WHERE P eid %%(p)s' % num, {'p': p[0][0]})

 ...

 <resultset 'INSERT Version V: V num "0.1.0", V version_of P WHERE P eid %(p)s' (1 rows): [765L] (('Version',))>

 <resultset 'INSERT Version V: V num "0.2.0", V version_of P WHERE P eid %(p)s' (1 rows): [766L] (('Version',))>

 >>> t = rql('INSERT Ticket T: T title "let us write more doc", T done_in V, '

             'T concerns P WHERE V num "0.1.0"', P eid %(p)s', {'p': p[0][0]})

 >>> commit()

Now let's see what the edition form builds for us.

.. sourcecode:: python

 >>> monkey_patch_session(session)

 >>> form = session.vreg['forms'].select('edition', session, rset=rql('Ticket T'))

 >>> html = form.render()

This creates an automatic entity form. The ``.render()`` call yields

an html (unicode) string. The html output is shown below (with

internal fieldset omitted).

Looking at the html output

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

The form enveloppe

''''''''''''''''''

.. sourcecode:: html

 <div class="iformTitle"><span>main informations</span></div>

 <div class="formBody">

  <form action="http://crater:9999/validateform" method="post" enctype="application/x-www-form-urlencoded"

        id="entityForm" onsubmit="return freezeFormButtons('entityForm');"

        class="entityForm" cubicweb:target="eformframe">

    <div id="progress">validating...</div>

    <fieldset>

      <input name="__form_id" type="hidden" value="edition" />

      <input name="__errorurl" type="hidden" value="http://perdu.com#entityForm" />

      <input name="__domid" type="hidden" value="entityForm" />

      <input name="__type:763" type="hidden" value="Ticket" />

      <input name="eid" type="hidden" value="763" />

      <input name="__maineid" type="hidden" value="763" />

      <input name="_cw_edited_fields:763" type="hidden"

             value="concerns-subject,done_in-subject,priority-subject,type-subject,title-subject,description-subject,__type,_cw_generic_field" />

      ...

    </fieldset>

   </form>

 </div>

The main fieldset encloses a set of hidden fields containing various

metadata, that will be used by the `edit controller` to process it

back correctly.

The `freezeFormButtons(...)` javascript callback defined on the

``onlick`` event of the form element prevents accidental multiple

clicks in a row.

The ``action`` of the form is mapped to the ``validateform`` controller

(situated in :mod:`cubicweb.web.views.basecontrollers`).

A full explanation of the validation loop is given in

:ref:`validation_process`.

.. _attributes_section:

The attributes section

''''''''''''''''''''''

We can have a look at some of the inner nodes of the form. Some fields

are omitted as they are redundant for our purposes.

.. sourcecode:: html

      <fieldset class="default">

        <table class="attributeForm">

          <tr class="title_subject_row">

            <th class="labelCol"><label class="required" for="title-subject:763">title</label></th>

            <td>

              <input id="title-subject:763" maxlength="128" name="title-subject:763" size="45"

                     tabindex="1" type="text" value="let us write more doc" />

            </td>

          </tr>

          ... (description field omitted) ...

          <tr class="priority_subject_row">

            <th class="labelCol"><label class="required" for="priority-subject:763">priority</label></th>

            <td>

              <select id="priority-subject:763" name="priority-subject:763" size="1" tabindex="4">

                <option value="important">important</option>

                <option selected="selected" value="normal">normal</option>

                <option value="minor">minor</option>

              </select>

              <div class="helper">importance</div>

            </td>

          </tr>

          ... (type field omitted) ...

          <tr class="concerns_subject_row">

            <th class="labelCol"><label class="required" for="concerns-subject:763">concerns</label></th>

            <td>

              <select id="concerns-subject:763" name="concerns-subject:763" size="1" tabindex="6">

                <option selected="selected" value="760">Foo</option>

              </select>

            </td>

          </tr>

          <tr class="done_in_subject_row">

            <th class="labelCol"><label for="done_in-subject:763">done in</label></th>

            <td>

              <select id="done_in-subject:763" name="done_in-subject:763" size="1" tabindex="7">

                <option value="__cubicweb_internal_field__"></option>

                <option selected="selected" value="761">Foo 0.1.0</option>

                <option value="762">Foo 0.2.0</option>

              </select>

              <div class="helper">version in which this ticket will be / has been  done</div>

            </td>

          </tr>

        </table>

      </fieldset>

Note that the whole form layout has been computed by the form

renderer. It is the renderer which produces the table

structure. Otherwise, the fields html structure is emitted by their

associated widget.

While it is called the `attributes` section of the form, it actually

contains attributes and *mandatory relations*. For each field, we

observe:

* a dedicated row with a specific class, such as ``title_subject_row``

  (responsability of the form renderer)

* an html widget (input, select, ...) with:

  * an id built from the ``rtype-role:eid`` pattern

  * a name built from the same pattern

  * possible values or preselected options

The relations section

'''''''''''''''''''''

.. sourcecode:: html

      <fieldset class="This ticket :">

        <legend>This ticket :</legend>

        <table class="attributeForm">

          <tr class="_cw_generic_field_None_row">

            <td colspan="2">

              <table id="relatedEntities">

                <tr><th>&#160;</th><td>&#160;</td></tr>

                <tr id="relationSelectorRow_763" class="separator">

                  <th class="labelCol">

                    <select id="relationSelector_763" tabindex="8"

                            onchange="javascript:showMatchingSelect(this.options[this.selectedIndex].value,763);">

                      <option value="">select a relation</option>

                      <option value="appeared_in_subject">appeared in</option>

                      <option value="custom_workflow_subject">custom workflow</option>

                      <option value="depends_on_object">dependency of</option>

                      <option value="depends_on_subject">depends on</option>

                      <option value="identical_to_subject">identical to</option>

                      <option value="see_also_subject">see also</option>

                    </select>

                  </th>

                  <td id="unrelatedDivs_763"></td>

                </tr>

              </table>

            </td>

          </tr>

        </table>

      </fieldset>

The optional relations are grouped into a drop-down combo

box. Selection of an item triggers a javascript function which will:

* show already related entities in the div of id `relatedentities`

  using a two-colown layout, with an action to allow deletion of

  individual relations (there are none in this example)

* provide a relation selector in the div of id `relationSelector_EID`

  to allow the user to set up relations and trigger dynamic action on

  the last div

* fill the div of id `unrelatedDivs_EID` with a dynamically computed

  selection widget allowing direct selection of an unrelated (but

  relatable) entity or a switch towards the `search mode` of

  |cubicweb| which allows full browsing and selection of an entity

  using a dedicated action situated in the left column boxes.

The buttons zone

''''''''''''''''

Finally comes the buttons zone.

.. sourcecode:: html

      <table width="100%">

        <tbody>

          <tr>

            <td align="center">

              <button class="validateButton" tabindex="9" type="submit" value="validate">

                <img alt="OK_ICON" src="http://myapp/datafd8b5d92771209ede1018a8d5da46a37/ok.png" />

                validate

              </button>

            </td>

            <td style="align: right; width: 50%;">

              <button class="validateButton"

                      onclick="postForm('__action_apply', 'button_apply', 'entityForm')"

                      tabindex="10" type="button" value="apply">

                <img alt="APPLY_ICON" src="http://myapp/datafd8b5d92771209ede1018a8d5da46a37/plus.png" />

                apply

              </button>

              <button class="validateButton"

                      onclick="postForm('__action_cancel', 'button_cancel', 'entityForm')"

                      tabindex="11" type="button" value="cancel">

                <img alt="CANCEL_ICON" src="http://myapp/datafd8b5d92771209ede1018a8d5da46a37/cancel.png" />

                cancel

              </button>

            </td>

          </tr>

        </tbody>

      </table>

The most notable artifacts here are the ``postForm(...)`` calls

defined on click events on these buttons. This function basically

submits the form.

.. _validation_process:

The form validation process

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

Preparation

~~~~~~~~~~~

After the (html) document is loaded, the ``setFormsTarget`` javascript

function dynamically transforms the DOM as follows. For all forms of

the DOM, it:

* sets the ``target`` attribute where there is a ``cubicweb:target``

  attribute (with the same value)

* appends an empty `IFRAME` element at the end

Let us have a look again at the form element. We have omitted some

irrelevant attributes.

.. sourcecode::html

  <form action="http://crater:9999/validateform" method="post"

        enctype="application/x-www-form-urlencoded"

        id="entityForm" cubicweb:target="eformframe"

        target="eformframe">

  ...

  </form>

Validation loop

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

On form submission, the form.action is invoked. Basically, the

``validateform`` controller is called and its output lands in the

specified ``target``, the iframe that was previously prepared.

Hence, the main page is not replaced, only the iframe contents. The

``validateform`` controller only outputs a tiny javascript fragment

which is then immediately executed.

.. sourcecode:: html

 <iframe width="0px" height="0px" name="eformframe" id="eformframe" src="javascript: void(0)">

   <script type="text/javascript">

     window.parent.handleFormValidationResponse('entityForm', null, null,

                                                [false, [2164, {"name-subject": "required field"}], null],

                                                null);

   </script>

 </iframe>

The ``window.parent`` part ensures the javascript function is called

on the right context (that is: the form element). We will describe its

parameters:

* first comes the form id (`entityForm`)

* then two optional callbacks for the success and failure case

* an array containing:

  * a boolean which indicates status (success or failure), and then, on error:

    * an array structured as ``[eid, {'rtype-role': 'error msg'}, ...]``

  * on success:

    * an url (string) representing the next thing to jump to

Given the array structure described above, it is quite simple to

manipulate the DOM to show the errors at appropriate places.

Explanation

~~~~~~~~~~~

This mecanism may seem a bit overcomplicated but we have to deal with

two realities:

* in the (strict) XHTML world, there are no iframes (hence the dynamic

  inclusion, tolerated by Firefox)

* no (or not all) browser(s) support file input field handling through

  ajax.