Calculated Fields Mockup

To implement:

• Modify the Field object:

  • Add new JSONB column calculation to the fields table
  • The values will look like this calculation: { type: "boolean|integer|string|string|array|date|date-time", expression: <EXPRESSION> }
  • Add new field type 'calculated'
  • A calculated field will be configured like this:

    Field.new(
      name: 'felt_stigma_score_calc',
      type: 'calculated',
      calculation: {
        type: 'number',
        expression: { sum: ['feelings_worthlessness', 'feeling_detached', 'feeling_badly_treated', ...}
      },
      display_name_en: 'Score'
    )
    

• Update the lookup values of the source fields to be numeric strings:

  Lookup.create_or_update!(
  unique_id: 'lookup-felt-stigma-scale',
  name_en: 'Felt Stigma Scale',
  locked: true,
  lookup_values: [
    { id: '0', display_text: 'Not at all (0 pts)' },
    { id: '1', display_text: 'A little bit (1 pt)' },
    { id: '2', display_text: 'A moderate amount (2 pts)' },
    { id: '3', display_text: 'A lot (3 pts)' }
  ]
  

• Update the RecordJsonValidatorService:

  • Use the calculation.type field property
  • Always permit null values
  • Make sure that existing constraints apply: eg. integers should range from -2_147_483_648 to 2_147_483_647

• Calculations will be performed on the front end.

  • See expression evaluator library app/javascript/libs/expressions/parse-expression.js
  • We implemented skip logic and conditional options using this expression library. See:
    • app/javascript/components/record-form/form/subforms/subform-dialog-fields/component.jsx
    • app/javascript/components/record-form/components/render-form-sections.js
  • Note that the lookup values are actually strings. The new sum and average functions can try to cast strings to int.