withForm.js

/**
 * Loads a DuckEntityForm and pre-populates it with the value from a singleDuck
 *
 * Note that you need to map the form properties into your component props separately using mapStateToProps.  i.e.
 *
 * const tacos = DuckEntity();
 * const tacoForm = DuckEntityForm();
 *
 * function mapDucksToProps (props) {
 *   const parentDuck = singleDuck(tacos, props.tacoId);
 *   
 *   return: {
 *       parentDuck,
 *       formDuck: withForm(parentDuck, tacoForm)
 *   }
 * }
 *
 * @param entityDuck    The entity to be fetched, should be a singleDuck
 * @param formDuck      The form to be populated
 * @param transformLoad Optionally alter model when loading
 */
export const withForm = (entityDuck, formDuck, transformLoad = (model) => model) =>
  dependentDuck(entityDuck, ({value, meta}) =>
    customDuck(formDuck, {
      load: () => dispatch(formDuck.actions.load(transformLoad(value))), // loads the value into RRF
      read: (state) => ({
        value: state[formDuck.name],
        meta: {
          ...meta,
          ready: meta.ready && state[formDuck.name].model.id === value.id // holds off on setting the 'ready' flag until the `formDuck.actions.load` call has finished.
        }
      })
    })
);