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.
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.
openforms.formio.service
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 renderers <developers_backend_core_submission_renderer>.
Whenever a component plugin is registered, the openforms.formio.registry.BasePlugin.formatter class attribute must be specified.
format_value
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 openforms.formio.registry.BasePlugin.normalizer.
normalize_value_for_component
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 openforms.formio.registry.BasePlugin.mutate_config_dynamically. It receives the current openforms.submissions.models.Submission instance and a mapping of all the variable names and values at the time.
get_dynamic_configuration
For an example of a custom field type, see 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 openforms.formmio.service.rewrite_formio_components_for_request).
openforms.formio.service
openforms.formio.registry.BasePlugin
Using our usual extension pattern <developers_extending> you can register your own types.
Extensions should inherit from 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 = DefaultFormatterYou can find some examples in openforms.formio.components.custom.
openforms.formio.dynamic_config
openforms.formio.formatters
openforms.formio.rendering