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Custom Validation Rules

Beyond standard FHIR profile validation, organizations often need to enforce site-specific policies on FHIR resources. You can implement custom validation logic in Ballerina by combining the built-in FHIR validator with your own business rules.

Approach​

The FHIR validator package validates resources against base FHIR models and profile-constrained types. For additional organizational rules, you can write Ballerina functions that inspect the parsed resource and return errors when constraints are violated.

A typical pattern is:

  1. Validate the resource against the FHIR specification using validator:validate().
  2. Parse the resource into a typed Ballerina record.
  3. Apply custom business rules to the parsed record.
  4. Aggregate any validation errors from both steps.
import ballerina/io;
import ballerinax/health.fhir.r4;
import ballerinax/health.fhir.r4.international401;
import ballerinax/health.fhir.r4.validator;

public function main() returns error? {

    json body = {
        "resourceType": "Patient",
        "id": "591841",
        "name": [ {
            "family": "Cushing",
            "given": [ "Caleb" ]
        } ]
    };

    // Step 1: Validate against the FHIR profile
    r4:FHIRValidationError? fhirValidation = validator:validate(body, international401:Patient);

    if fhirValidation is r4:FHIRValidationError {
        io:println("FHIR validation failed: ", fhirValidation.message());
    }

    // Step 2: Apply custom business rules
    international401:Patient patient = check body.cloneWithType();
    string[] customErrors = checkBusinessRules(patient);

    foreach string err in customErrors {
        io:println("Custom rule violation: ", err);
    }
}

function checkBusinessRules(international401:Patient patient) returns string[] {
    string[] errors = [];

    // Example: require at least one identifier
    if patient.identifier is () || (<r4:Identifier[]>patient.identifier).length() == 0 {
        errors.push("Patient must have at least one identifier");
    }

    return errors;
}

Common Custom Rule Categories​

CategoryExamples
Identifier requirementsMRN must be present, NPI format validation
Temporal constraintsDates in valid ranges, encounters not in the future
Referential integrityReferenced resources must exist
Business logicMedication dosage within safe ranges
Data qualityCompleteness checks, preferred coding systems