One-hot category

onehot-category renders a select and submits one column per option: 1 for the selected option, 0 for every other. The model gets its one-hot encoding; people get one readable choice. No hidden fields are involved.

With Rain selected, the transport received weather_clear: 0, weather_cloudy: 0, weather_rain: 1.

{
  id: "weather",
  kind: "onehot-category",
  label: "Weather condition",
  defaultValue: "rain",
  required: true,
  options: [
    { label: "Clear", value: "clear", mappedTo: "weather_clear" },
    { label: "Cloudy", value: "cloudy", mappedTo: "weather_cloudy" },
    { label: "Rain", value: "rain", mappedTo: "weather_rain" },
  ],
}

request.modelValues for that selection:

{ "weather_clear": 0, "weather_cloudy": 0, "weather_rain": 1 }

The field’s own value stays "rain"; that is what inputs[].value holds, and what displayValues shows when the field has a displayKey. With no selection, every column is 0; add required: true when the model needs exactly one 1.

Options

Property	Type	Meaning
label	string	Text in the select.
value	string	The field’s value when the option is selected.
mappedTo	target or per-backend map	The column that receives 1 or 0 for this option.

The field-level mappedTo is not used; each option names its own column. Per-backend maps work as for any field, so a column can have a different name for each backend.

Rules

• Every option needs a target for the backend being submitted. A missing target fails the submission.
• Two options that resolve to the same column fail.
• Values are numbers 0 and 1, never booleans or strings.

Restore a selection from model columns

When you load saved model inputs, resolveOneHotDisplayValue from mlform/builtins turns the columns back into the option value:

import { resolveOneHotDisplayValue } from "mlform/builtins";

const weather = resolveOneHotDisplayValue(weatherField, savedModelValues); // "rain"
mounted.form.setValues({ weather });

It accepts 1, "1", or true as selected, returns undefined when no column is selected, and throws when more than one is. Pass { backend } as the third argument to read per-backend targets.

When to use mapped category instead

Use mapped-category when an option sets arbitrary values, several non-binary features, or values that people should see in other fields.