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This documentation covers files located at: Questionnaire Item Choice

Questionnaire Item Choice Component

The Questionnaire Item Choice Component is a little more complex than the other questionnaire item components. It needs to handle the answerOptions and therefore it must retrieve them from the QuestionnaireItem.answerOption property.

Choice Item Handling & Option Matching

Concept

A critical requirement for Choice items is that the QuestionnaireResponseItem.answer property must be matched against available options before the patching process occurs. This ensures that only valid values, consistent with the current Questionnaire definition, are set.

Initialization Workflow

To achieve this, option retrieval must be completed before the answer FormArray is initialized. Consequently, the setup must occur prior to the QuestionnaireItemBaseComponent.ngOnInit call:

1. We override ngOnInit.
2. We set up and filter for our options.
3. Finally, we call super.ngOnInit() to proceed with the standard lifecycle.

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Special Case: itemValueKey

In standard items, the itemValueKey is mapped directly to a specific FHIR key (e.g., valueString or valueInteger), as detailed in the Questionnaire Item Base Component.

However, Choice elements present a unique challenge because they support polymorphic value types within their options (e.g., valueString, valueInteger, or valueCoding). To handle this flexibility without hardcoding a single FHIR key, we use a specialized approach:

• Dedicated Wrapper: We use a custom key called CHOICE_ANSWER_WRAPPER.
• Object-Level Handling: Instead of managing primitive values, the Choice element handles the entire Response object.
• Custom Comparison: We implemented a custom comparison function to ensure that objects are compared by their internal structure/identity rather than just primitive equality.

Dynamic Response Building

When the final response is constructed, the QuestionnaireLogicService unpacks the value stored under the CHOICE_ANSWER_WRAPPER. This architecture allows us to:

1. Keep FormGroups consistent and simple.
2. Remain dynamic across different value types.
3. Theoretically support a mix of different "value" types within the same set of options.

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Supported Item Features

Feature	Config Key	Logic
Label Text	item.text	This component
Answer Options	item.answerOption	This component
Enable When	item.enableWhen	Item Renderer
Enable When Behaviour	item.enableWhenBehaviour	Item Renderer
Required	item.required	Item Renderer
Repeats	item.repeats	Item Renderer

Extension Features

Feature	Extension URL	Key / Value Type
Translation	http://hl7.org/fhir/StructureDefinition/translation	Complex Type
Min Occurrences	http://hl7.org/fhir/StructureDefinition/questionnaire-minOccurs	valueInteger
Max Occurrences	http://hl7.org/fhir/StructureDefinition/questionnaire-maxOccurs	valueInteger
SDC Enable When	http://hl7.org/fhir/uv/sdc/StructureDefinition/sdc-questionnaire-enableWhenExpression	valueExpression
Item Control	http://hl7.org/fhir/StructureDefinition/questionnaire-itemControl	valueCodeableConcept: radio-button
Choice Orientation	http://hl7.org/fhir/StructureDefinition/questionnaire-choiceOrientation	valueCode: horizontal | vertical

Technical Implementation Details

For detailed information regarding technical implementation, please refer to the following:

• Questionnaire Base Component
• Questionnaire Item Renderer
• Questionnaire-Enable-When Service