Other Validation Types

Beyond date-based validation and expression-based validation, the Form Engine supports the following validator types.

conditionalAnswered

Use a conditionalAnswered validator when a question should only be answered if another question was answered with one of a specific set of values. If the question has a value while the referenced question is unanswered, or was answered with a value outside the allowed set, validation fails with the provided message. Note that the comparison only works for single-valued referenced questions — when the referenced question holds an array (a checkbox or multi-select question), the validator cannot match it against referenceQuestionAnswers and fails whenever this question is answered.

The validator takes:

referenceQuestionId: the id of the question this one depends on.
referenceQuestionAnswers: an array of allowed answer values (concept UUIDs for coded questions) for the referenced question.
message: the error message shown when validation fails.

The example below is from a form where a hospitalization diagnosis should only be provided if the patient was marked as hospitalized:

{
  "label": "Hospitalization diagnosis",
  "type": "obs",
  "id": "hospitalizedDiagnosis",
  "questionOptions": {
    "concept": "a8a07a48-1350-11df-a1f1-0026b9348838",
    "rendering": "problem"
  },
  "validators": [
    {
      "type": "conditionalAnswered",
      "message": "Providing diagnosis but didn't answer that patient was hospitalized in question",
      "referenceQuestionId": "wasHospitalized",
      "referenceQuestionAnswers": ["a899b35c-1350-11df-a1f1-0026b9348838"]
    }
  ]
}

Numeric constraints via questionOptions

For number and decimal renderings, the engine also derives validators from questionOptions — no validators array needed:

min and max: bounds for the value. The engine registers these validators only when both are present.
minLength and maxLength: bounds on the length of the entered value.
disallowDecimals: when true, accepts unsigned whole digits only — any other character fails validation, including a decimal point but also a minus sign on a negative integer. The error message is the disallowDecimals translation key, so provide a translation for it or users see the raw key.

{
  "label": "Number of children",
  "type": "obs",
  "id": "numChildren",
  "questionOptions": {
    "concept": "a8a04b76-1350-11df-a1f1-0026b9348838",
    "rendering": "number",
    "min": "0",
    "max": "30",
    "disallowDecimals": true
  }
}

Expression-based Validation Injecting Data Sources