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Core: form.io integration

Open Forms uses form.io under the hood to build and render forms, and then adds its own layers on top of that, such as:

  • implementing multi-step forms where every step is a form.io definition
  • evaluating backend logic using data from earlier steps
  • dynamically adapting form.io definitions as needed

This means that we process the form.io datastructures in the backend, using Python. All the code for this is organized in the openforms.formio package.

.. versionchanged:: 2.1.0

    ``openforms.custom_field_types`` was refactored into the ``openforms.formio`` package,
    and all of the separate registries (formatters, normalizers...) were merged into a
    single compoment registry.

Supported features

.. currentmodule:: openforms.formio.service

Formatting values for display

Value formatting is done for displaying form submission data summaries, rendering confirmation PDFs and emails... It is aware if it's in a HTML context or not. It is heavily used in the :ref:`renderers <developers_backend_core_submission_renderer>`.

Whenever a component plugin is registered, the :attr:`openforms.formio.registry.BasePlugin.formatter` class attribute must be specified.

.. autofunction:: format_value
    :noindex:

Normalizing input data

Data for a component can be sourced from external systems that employ different formatting rules compared to what form.io expects. Normalizing this data helps to be able to make proper comparisons at different stages in the submission life-cycle.

You can opt-in to this by configuring :attr:`openforms.formio.registry.BasePlugin.normalizer`.

.. autofunction:: normalize_value_for_component
    :noindex:

Dynamically modifying component configuration

Certain component types require on-the-fly configuration rewriting, such as applying global configuration options that may change independently from when the form is actually being designed.

Dynamic rewriting is enabled by implementing :meth:`openforms.formio.registry.BasePlugin.mutate_config_dynamically`. It receives the current :class:`openforms.submissions.models.Submission` instance and a mapping of all the variable names and values at the time.

.. autofunction:: get_dynamic_configuration
    :noindex:

For an example of a custom field type, see :class:`openforms.formio.components.custom.Date`.

Finally, the resulting resolved component definitions are evaluated with the template engine where variable values are evaluated for compoment labels, descriptions... and configuration based on the HTTP request is performed (see :func:`openforms.formmio.service.rewrite_formio_components_for_request`).

Reference

Public API - openforms.formio.service

.. automodule:: openforms.formio.service
    :members:


.. autoclass:: openforms.formio.registry.BasePlugin
    :members:
    :exclude-members: verbose_name

Extending

Using our :ref:`usual extension pattern <developers_extending>` you can register your own types.

Extensions should inherit from :class:`openforms.formio.registry.BasePlugin` or implement the same protocol(s) and be registered with their form.io type:

from openforms.formio.formatters.formio import DefaultFormatter
from openforms.formio.registry import BasePlugin

@register("myCustomType")
class MyComponent(BasePlugin):
    formatter = DefaultFormatter

You can find some examples in openforms.formio.components.custom.

Private API

Module: openforms.formio.dynamic_config

.. automodule:: openforms.formio.dynamic_config
    :members:

Module: openforms.formio.formatters

.. automodule:: openforms.formio.formatters
    :members:

Module: openforms.formio.rendering

.. automodule:: openforms.formio.rendering
    :members: