HTML form construction#

CubicWeb provides the somewhat usual form / field / widget / renderer abstraction to provide generic building blocks which will greatly help you in building forms properly integrated with CubicWeb (coherent display, error handling, etc…), while keeping things as flexible as possible.

A form basically only holds a set of fields, and has te be bound to a renderer which is responsible to layout them. Each field is bound to a widget that will be used to fill in value(s) for that field (at form generation time) and ‘decode’ (fetch and give a proper Python type to) values sent back by the browser.

The field should be used according to the type of what you want to edit. E.g. if you want to edit some date, you’ll have to use the cubicweb.web.formfields.DateField. Then you can choose among multiple widgets to edit it, for instance cubicweb.web.formwidgets.TextInput (a bare text field), DateTimePicker (a simple calendar) or even JQueryDatePicker (the JQuery calendar). You can of course also write your own widget.

Exploring the available forms#

A small excursion into a CubicWeb shell is the quickest way to discover available forms (or application objects in general).

>>> from pprint import pprint
>>> pprint( session.vreg['forms'] )
{'base': [<class 'cubicweb.web.views.forms.FieldsForm'>,
          <class 'cubicweb.web.views.forms.EntityFieldsForm'>],
 'changestate': [<class 'cubicweb.web.views.workflow.ChangeStateForm'>,
                 <class 'cubicweb_tracker.views.forms.VersionChangeStateForm'>],
 'composite': [<class 'cubicweb.web.views.forms.CompositeForm'>,
               <class 'cubicweb.web.views.forms.CompositeEntityForm'>],
 'deleteconf': [<class 'cubicweb.web.views.editforms.DeleteConfForm'>],
 'edition': [<class 'cubicweb.web.views.autoform.AutomaticEntityForm'>,
             <class 'cubicweb.web.views.workflow.TransitionEditionForm'>,
             <class 'cubicweb.web.views.workflow.StateEditionForm'>],
 'logform': [<class 'cubicweb.web.views.basetemplates.LogForm'>],
 'massmailing': [<class 'cubicweb.web.views.massmailing.MassMailingForm'>],
 'muledit': [<class 'cubicweb.web.views.editforms.TableEditForm'>]}

The two most important form families here (for all practical purposes) are base and edition. Most of the time one wants alterations of the AutomaticEntityForm to generate custom forms to handle edition of an entity.

The Automatic Entity Form#

Anatomy of a choices function#

Let’s have a look at the ticket_done_in_choices function given to the choices parameter of the relation tag that is applied to the (‘Ticket’, ‘done_in’, ‘*’) relation definition, as it is both typical and sophisticated enough. This is a code snippet from the tracker cube.

The Ticket entity type can be related to a Project and a Version, respectively through the concerns and done_in relations. When a user is about to edit a ticket, we want to fill the combo box for the done_in relation with values pertinent with respect to the context. The important context here is:

  • creation or modification (we cannot fetch values the same way in either case)

  • __linkto url parameter given in a creation context

from cubicweb.web import formfields

def ticket_done_in_choices(form, field):
    entity = form.edited_entity
    # first see if its specified by __linkto form parameters
    linkedto = form.linked_to[('done_in', 'subject')]
    if linkedto:
        return linkedto
    # it isn't, get initial values
    vocab = field.relvoc_init(form)
    veid = None
    # try to fetch the (already or pending) related version and project
    if not entity.has_eid():
        peids = form.linked_to[('concerns', 'subject')]
        peid = peids and peids[0]
        peid = entity.project.eid
        veid = entity.done_in and entity.done_in[0].eid
    if peid:
        # we can complete the vocabulary with relevant values
        rschema = form._cw.vreg.schema['done_in'].rdef('Ticket', 'Version')
        rset = form._cw.execute(
            'Any V, VN ORDERBY version_sort_value(VN) '
            'WHERE V version_of P, P eid %(p)s, V num VN, '
            'V in_state ST, NOT ST name "published"', {'p': peid}, 'p')
        vocab += [(v.view('combobox'), v.eid) for v in rset.entities()
                  if rschema.has_perm(form._cw, 'add', toeid=v.eid)
                  and v.eid != veid]
    return vocab

The first thing we have to do is fetch potential values from the __linkto url parameter that is often found in entity creation contexts (the creation action provides such a parameter with a predetermined value; for instance in this case, ticket creation could occur in the context of a Version entity). The RelationField field class provides a relvoc_linkedto() method that gets a list suitably filled with vocabulary values.

linkedto = field.relvoc_linkedto(form)
if linkedto:
    return linkedto

Then, if no __linkto argument was given, we must prepare the vocabulary with an initial empty value (because done_in is not mandatory, we must allow the user to not select a verson) and already linked values. This is done with the relvoc_init() method.

vocab = field.relvoc_init(form)

But then, we have to give more: if the ticket is related to a project, we should provide all the non published versions of this project (Version and Project can be related through the version_of relation). Conversely, if we do not know yet the project, it would not make sense to propose all existing versions as it could potentially lead to incoherences. Even if these will be caught by some RQLConstraint, it is wise not to tempt the user with error-inducing candidate values.

The “ticket is related to a project” part must be decomposed as:

  • this is a new ticket which is created is the context of a project

  • this is an already existing ticket, linked to a project (through the concerns relation)

  • there is no related project (quite unlikely given the cardinality of the concerns relation, so it can only mean that we are creating a new ticket, and a project is about to be selected but there is no __linkto argument)


the last situation could happen in several ways, but of course in a polished application, the paths to ticket creation should be controlled so as to avoid a suboptimal end-user experience

Hence, we try to fetch the related project.

veid = None
if not entity.has_eid():
    peids = form.linked_to[('concerns', 'subject')]
    peid = peids and peids[0]
    peid = entity.project.eid
    veid = entity.done_in and entity.done_in[0].eid

We distinguish between entity creation and entity modification using the Entity.has_eid() method, which returns False on creation. At creation time the only way to get a project is through the __linkto parameter. Notice that we fetch the version in which the ticket is done_in if any, for later.


the implementation above assumes that if there is a __linkto parameter, it is only about a project. While it makes sense most of the time, it is not an absolute. Depending on how an entity creation action action url is built, several outcomes could be possible there

If the ticket is already linked to a project, fetching it is trivial. Then we add the relevant version to the initial vocabulary.

if peid:
    rschema = form._cw.vreg.schema['done_in'].rdef('Ticket', 'Version')
    rset = form._cw.execute(
        'Any V, VN ORDERBY version_sort_value(VN) '
        'WHERE V version_of P, P eid %(p)s, V num VN, '
        'V in_state ST, NOT ST name "published"', {'p': peid})
    vocab += [(v.view('combobox'), v.eid) for v in rset.entities()
              if rschema.has_perm(form._cw, 'add', toeid=v.eid)
              and v.eid != veid]


we have to defend ourselves against lack of a project eid. Given the cardinality of the concerns relation, there must be a project, but this rule can only be enforced at validation time, which will happen of course only after form subsmission

Here, given a project eid, we complete the vocabulary with all unpublished versions defined in the project (sorted by number) for which the current user is allowed to establish the relation.

Building self-posted form with custom fields/widgets#

Sometimes you want a form that is not related to entity edition. For those, you’ll have to handle form posting by yourself. Here is a complete example on how to achieve this (and more).

Imagine you want a form that selects a month period. There are no proper field/widget to handle this in CubicWeb, so let’s start by defining them:

# let's have the whole import list at the beginning, even those necessary for
# subsequent snippets
from logilab.common import date
from logilab.mtconverter import xml_escape
from cubicweb.view import View
from cubicweb.predicates import match_kwargs
from cubicweb.web import RequestError, ProcessFormError
from cubicweb.web import formfields as fields, formwidgets as wdgs
from cubicweb.web.views import forms, calendar

class MonthSelect(wdgs.Select):
    """Custom widget to display month and year. Expect value to be given as a
    date instance.

    def format_value(self, form, field, value):
        return u'%s/%s' % (value.year, value.month)

    def process_field_data(self, form, field):
        val = super(MonthSelect, self).process_field_data(form, field)
            year, month = val.split('/')
            year = int(year)
            month = int(month)
            return, month, 1)
        except ValueError:
            raise ProcessFormError(
                form._cw._('badly formated date string %s') % val)

class MonthPeriodField(fields.CompoundField):
    """custom field composed of two subfields, 'begin_month' and 'end_month'.

    It expects to be used on form that has 'mindate' and 'maxdate' in its
    extra arguments, telling the range of month to display.

    def __init__(self, *args, **kwargs):
        kwargs.setdefault('widget', wdgs.IntervalWidget())
        super(MonthPeriodField, self).__init__(
                                choices=self.get_range, sort=False,
                                choices=self.get_range, sort=False,
                                widget=MonthSelect())], *args, **kwargs)

    def get_range(form, field):
        mindate = date.todate(form.cw_extra_kwargs['mindate'])
        maxdate = date.todate(form.cw_extra_kwargs['maxdate'])
        assert mindate <= maxdate
        _ = form._cw._
        months = []
        while mindate <= maxdate:
            label = '%s %s' % (_(calendar.MONTHNAMES[mindate.month - 1]),
            value = field.widget.format_value(form, field, mindate)
            months.append( (label, value) )
            mindate = date.next_month(mindate)
        return months

    def get_mindate(form, field):
        return form.cw_extra_kwargs['mindate']

    def get_maxdate(form, field):
        return form.cw_extra_kwargs['maxdate']

    def process_posted(self, form):
        for field, value in super(MonthPeriodField, self).process_posted(form):
            if == 'end_month':
                value = date.last_day(value)
            yield field, value

Here we first define a widget that will be used to select the beginning and the end of the period, displaying months like ‘<month> YYYY’ but using ‘YYYY/mm’ as actual value.

We then define a field that will actually hold two fields, one for the beginning and another for the end of the period. Each subfield uses the widget we defined earlier, and the outer field itself uses the standard IntervalWidget. The field adds some logic:

  • a vocabulary generation function get_range, used to populate each sub-field

  • two ‘value’ functions get_mindate and get_maxdate, used to tell to subfields which value they should consider on form initialization

  • overriding of process_posted, called when the form is being posted, so that the end of the period is properly set to the last day of the month.

Now, we can define a very simple form:

class MonthPeriodSelectorForm(forms.FieldsForm):
    __regid__ = 'myform'
    __select__ = match_kwargs('mindate', 'maxdate')

    form_buttons = [wdgs.SubmitButton()]
    form_renderer_id = 'onerowtable'
    period = MonthPeriodField()

where we simply add our field, set a submit button and use a very simple renderer (try others!). Also we specify a selector that ensures form will have arguments necessary to our field.

Now, we need a view that will wrap the form and handle post when it occurs, simply displaying posted values in the page:

class SelfPostingForm(View):
    __regid__ = 'myformview'

    def call(self):
        mindate, maxdate =, 1, 1),, 1, 1)
        form = self._cw.vreg['forms'].select(
            'myform', self._cw, mindate=mindate, maxdate=maxdate, action='')
            posted = form.process_posted()
            self.w(u'<p>posted values %s</p>' % xml_escape(repr(posted)))
        except RequestError: # no specified period asked
        form.render(w=self.w, formvalues=self._cw.form)

Notice usage of the process_posted() method, that will return a dictionary of typed values (because they have been processed by the field). In our case, when the form is posted you should see a dictionary with ‘begin_month’ and ‘end_month’ as keys with the selected dates as value (as a python date object).