Ignixa.FhirPath 0.0.127

Ignixa.FhirPath

FHIRPath expression evaluation engine for FHIR resources. Provides a high-performance implementation of the FHIRPath specification for querying and navigating FHIR data structures.

Why Use This Package?

• Standards-compliant: Implements the FHIRPath specification
• High-performance: Includes compiled delegate mode for common patterns
• Modern architecture: Works with IElement from Ignixa.Abstractions
• Extensible: Add custom functions and evaluation logic

Installation

dotnet add package Ignixa.FhirPath

Quick Start

Evaluating FHIRPath Expressions

using Ignixa.FhirPath.Parser;
using Ignixa.FhirPath.Evaluation;
using Ignixa.Abstractions;

// Parse a FHIRPath expression
var parser = new FhirPathParser();
var expression = parser.Parse("Patient.name.family");

// Evaluate against a resource
var evaluator = new FhirPathEvaluator();
IElement patientElement = GetYourPatientElement();

IEnumerable<IElement> results = evaluator.Evaluate(patientElement, expression);

// Extract values
foreach (var result in results)
{
    Console.WriteLine(result.Value); // Prints family names
}

Using the Compiled Delegate Mode (Faster)

For better performance on repeated evaluations:

using Ignixa.FhirPath.Evaluation;

// Set up compiler with fallback evaluator
var evaluator = new FhirPathEvaluator();
var compiler = new FhirPathDelegateCompiler(evaluator);

// Parse expression
var expression = parser.Parse("telecom.where(system='phone').value");

// Try to compile (falls back to interpreter if not supported)
var compiled = compiler.TryCompile(expression);

if (compiled != null)
{
    // Use compiled delegate (80% faster for common patterns)
    var context = new EvaluationContext();
    var results = compiled(patientElement, context);
}
else
{
    // Fallback to interpreter
    var results = evaluator.Evaluate(patientElement, expression);
}

Common FHIRPath Patterns

// Simple path navigation
"Patient.name.family"                    // Get all family names

// Filtering with where()
"telecom.where(system='phone')"          // Get phone telecoms
"name.where(use='official').family"      // Get official family name

// Existence checks
"identifier.exists()"                    // Has any identifiers?
"name.family.exists()"                   // Has family name?

// First/single element
"name.first().family"                    // First family name
"identifier.where(system='SSN').value"   // SSN value

// Boolean expressions
"active = true"                          // Is patient active?
"birthDate < @2000-01-01"               // Born before 2000

Working with Evaluation Context

using Ignixa.FhirPath.Evaluation;

var context = new EvaluationContext();

// Set variables for use in expressions
context.SetVariable("minDate", someDate);

// Evaluate expression using context
var expression = parser.Parse("birthDate > %minDate");
var results = evaluator.Evaluate(patientElement, expression, context);

Supported FHIRPath Features

Compiled Mode (High Performance)

• Simple paths: name, identifier
• Two-level paths: name.family, identifier.value
• Where clauses: telecom.where(system='phone')
• Common functions: first(), exists()

Interpreter Mode (Full Compatibility)

• All FHIRPath 2.0 operators
• All standard functions
• Complex nested expressions
• Type checking and conversions

Performance Notes

The FhirPathDelegateCompiler compiles ~80% of common search parameter patterns to optimized delegates:

• Simple paths: 30% of patterns (e.g., name)
• Two-level paths: 40% of patterns (e.g., name.family)
• Where clauses: 15% of patterns (e.g., telecom.where(system='phone'))
• Functions: 10% of patterns (e.g., name.first())

Unsupported expressions automatically fall back to the interpreted mode.

Advanced Usage

Custom Function Registration

// Extend FhirPathEvaluator with custom functions
public class MyCustomEvaluator : FhirPathEvaluator
{
    protected override IEnumerable<IElement> EvaluateFunctionCall(
        IEnumerable<IElement> focus,
        FunctionCallExpression func,
        EvaluationContext context)
    {
        if (func.FunctionName == "myCustomFunc")
        {
            // Implement custom logic
            return focus.Where(e => /* your logic */);
        }

        return base.EvaluateFunctionCall(focus, func, context);
    }
}

Related Packages

• Ignixa.Abstractions: Provides IElement and IType interfaces
• Ignixa.Serialization: Parse JSON/XML to IElement trees
• Ignixa.Search: Uses FHIRPath for search parameter extraction
• Ignixa.Validation: Uses FHIRPath for constraint evaluation

Specification Compliance

This implementation follows the FHIRPath N1 specification.

License

MIT License - see LICENSE file in repository root