fhir-schema codegen

Library that generates language-specific models from FHIR StructureDefinition using type-schema (Github), enabling developers to work with strongly-typed FHIR resources in their preferred programming language.

How does it work?

fhir-schema-codegen uses a two-step process:

1. Type-Schema Transformation: Converts FHIR StructureDefinition into type-schema format, which provides a flat and denormalized representation for easier data access.

2. Template-Based Generation: Uses generators to transform the type-schema into language-specific models for each supported language (TypeScript, C#, Python, etc.).

Supports custom template-based generators allowing you to add new language support, customize the output format of available generators, and implement language-specific features.

Join our community at FHIR Chat to learn more and contribute!

Installation

# Install globally
npm install -g @fhirschema/codegen

# Or use with npx
npx @fhirschema/codegen [command] [options]

Usage

The fhir-schema codegen provides several commands to work with FHIR definitions and generate code:

# Generate code
fscg generate -g typescript -o ./fhir.r4.sdk -p [email protected]

# List all available (built in) generators
fscg generators

Command Reference

generate

Generates code from core FHIR Implementation Guide:

fscg generate -g <generator> -o <output-dir> -p <fhir.package@version>

Options:

• -g, --generator <generator> - Generator to use (typescript, csharp, python)
• -o, --output <directory> - Output directory
• -p, --packages <packages...> - Available published FHIR IGs
• -f, --files <files...> - TypeSchema source *.ndjson files
• --custom-generator <path> - Path to your custom generator template
• --with-debug-comment - Enable debug comments in generated code
• --profile - Enable profile generation

Example:

fscg generate -g typescript -o ./fhir.r4.sdk -p [email protected]

Create a custom generator template

generators

Lists of the available generators:

fscg generators

create-generator

Creates a new custom generator template:

fscg create-generator -o <output-directory>

Options:

• -o, --output <directory> - Output directory (default: ./fhirschema-generators)

Example:

fscg create-generator -o ./my-generator

Supported Generators

The library supports multiple language generators, each providing type-safe FHIR resource handling. Below are the currently supported generators with examples and implementation details:

TypeScript Generator

The TypeScript generator creates a fully typed SDK with interfaces for all FHIR resources. Example implementation in ./example/typescript/:

import { Patient } from './aidbox/types/hl7-fhir-r4-core';

const patient: Patient = {
  identifier: [{ system: 'http://org.io/id', value: '0000-0000' }],
  name: [{ given: ['John'], family: 'Doe' }],
  gender: 'male',
  birthDate: '1990-01-01',
};

Generate TypeScript SDK:

fscg generate -g typescript -o ./ts-sdk -p [email protected]

# With debug comments:
fscg generate -g typescript -o ./ts-sdk -p [email protected] --with-debug-comment

C# Generator

The C# generator produces strongly-typed C# classes for FHIR resources. Example implementation in ./example/csharp/:

using Aidbox.FHIR.R4.Core;

var patient = new Patient
{
    Identifier = [new Identifier { System = "http://hl7.org/fhir/us/CodeSystem/identity", Value = "0000-0000" }],
    Name = [new HumanName { Given = ["John"], Family = "Doe" }],
    Gender = "male",
    BirthDate = "1990-01-01",
};

Generate C# SDK:

fscg generate -g csharp -o ./csharp-sdk -p [email protected]

Python Generator

The Python generator creates Python classes. Example implementation in ./example/python/:

from aidbox.hl7_fhir_r4_core.base import HumanName, Identifier
from aidbox.hl7_fhir_r4_core import Patient

patient = Patient(
    identifier=[Identifier(system="http://org.io/id", value="0000-0000")],
    name=[HumanName(given=["John"], family="Doe")],
    gender="male",
    birth_date="1990-01-01",
)

Generate Python SDK:

fscg generate -g python -o ./python-sdk -p [email protected]

# With options:
fscg generate -g python -o ./python-sdk -p [email protected] --py-sdk-package my_package --py-allow-extra-fields

Custom Generators

You can create custom generators to support additional languages or specialized formats. The generator system is extensible and allows you to:

• Create generators for new languages
• Customize the output format
• Add language-specific features

Generator inherits from base Generator class and implements generate() method to produce target language code based on type-schema (see ./src/generators/typescript/index.ts)

For more information on creating and using custom generators, see the Generators Registry documentation.

TypeScript Example

import { Generator, type GeneratorOptions, NestedTypeSchema, TypeSchema } from '@fhirschema/codegen';
import path from 'node:path';

export interface CustomGeneratorOptions extends GeneratorOptions {
    // Add custom options here
}

const typeMap :  Record<string, string> = {
    'boolean': 'boolean',
    'integer': 'number',
    'decimal': 'number',
    'positiveInt': 'number',
    'number': 'number'
}

export class CustomGenerator extends Generator {
    constructor(opts: CustomGeneratorOptions) {
        super({
            ...opts,
            staticDir: path.resolve(__dirname, '../static'),
        });
    }

    generateType(schema: TypeSchema | NestedTypeSchema) {
        let base = schema.base ? 'extends ' + schema.base.name : '';
        this.curlyBlock(['export', 'interface', schema.identifier.name, base], () => {
            if (schema.fields) {
                for (const [fieldName, field] of Object.entries(schema.fields)) {
                    if ('choices' in field) continue;
                    let fieldSymbol = fieldName;
                    if (!field.required) {
                        fieldSymbol += '?';
                    }
                    if (field.type.kind == 'primitive-type') {
                        type = typeMap[field.type.name] || 'string'
                    } else {
                        type = field.type.name;
                    }
                    this.lineSM(fieldSymbol, ':', type + (field.array ? '[]' : ''));
                }
            }
        });
        this.line();
    }

    generate() {
        this.dir('src', async () => {
            this.file('types.ts', () => {
                for (let schema of this.loader.complexTypes()) {
                    this.generateType(schema);
                }
            });

            for (let schema of this.loader.resources()) {
                this.file(schema.identifier.name + ".ts", () => {
                    if (schema.dependencies) {
                        for (let dep of schema.dependencies.filter(d => d.kind == 'complex-type')) {
                            this.lineSM('import', '{', dep.name, '}', 'from', '"./types.ts"');
                        }

                        for (let dep of schema.dependencies.filter(d => d.kind == 'resource')) {
                            this.lineSM('import', '{', dep.name, '}', 'from', '"./' + dep.name + '.ts"');
                        }
                    }

                    this.line();

                    if (schema.nested) {
                        for (let subtype of schema.nested) {
                            this.generateType(subtype);
                        }
                    }

                    this.line();

                    this.generateType(schema);
                });
            }
        })
    }
}

export function createGenerator(options: GeneratorOptions): Generator {
    return new CustomGenerator(options);
}

This will produce something like this:

import { CodeableConcept } from "./types.ts";
import { Reference } from "./types.ts";
import { HumanName } from "./types.ts";
import { Address } from "./types.ts";
import { Identifier } from "./types.ts";
import { Attachment } from "./types.ts";
import { BackboneElement } from "./types.ts";
import { ContactPoint } from "./types.ts";
import { Period } from "./types.ts";
import { DomainResource } from "./DomainResource.ts";

export interface PatientLink extends BackboneElement {
  other : Reference;
  type : string;
}

export interface PatientCommunication extends BackboneElement {
  language : CodeableConcept;
  preferred? : boolean;
}

export interface PatientContact extends BackboneElement {
  address? : Address;
  gender? : string;
  name? : HumanName;
  organization? : Reference;
  period? : Period;
  relationship? : CodeableConcept[];
  telecom? : ContactPoint[];
}


export interface Patient extends DomainResource {
  active? : boolean;
  address? : Address[];
  birthDate? : string;
  communication? : PatientCommunication[];
  contact? : PatientContact[];
  deceasedBoolean? : boolean;
  deceasedDateTime? : string;
  gender? : string;
  generalPractitioner? : Reference[];
  identifier? : Identifier[];
  link? : PatientLink[];
  managingOrganization? : Reference;
  maritalStatus? : CodeableConcept;
  multipleBirthBoolean? : boolean;
  multipleBirthInteger? : number;
  name? : HumanName[];
  photo? : Attachment[];
  telecom? : ContactPoint[];
}

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

Development Setup

1. Clone the repository

   git clone https://github.com/fhir-schema/fhir-schema-codegen.git
   cd fhir-schema-codegen

2. Install dependencies

   npm install

3. Build the project

   npm run build

4. Run tests

   npm test

Creating a New Generator

To create a new generator for a language:

1. Create a new directory in src/generators/ for your language
2. Create an index.ts file that exports a createGenerator function
3. Implement your generator by extending the base Generator class
4. Add your generator to the choices in the CLI in src/cli.ts

Alternatively, you can use the create-generator command to create a custom generator outside the main codebase.