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Boston, 19-21 June | @HL7 @FirelyTeam | #fhirdevdays18 | www.fhirdevdays.com

Build your own Vonk FHIR Facade

Christiaan Knaap, Furore

Audience

• Developers

• Architects

• .NET

• Code involved

Speaker

• Christiaan Knaap

• Firely

• 20 yr IT dev / analist / architect

• Lead dev of Vonk FHIR Server

• christiaan@fire.ly

• Zulip

Agenda

• Prerequisites

• What is (Vonk) FHIR Facade?

• ASP.Net Core

• Vonk Architecture

• Components

• Building a facade

• Exercise

• Sneak preview

Prerequisites

For this session

.NET programming

ASP.NET Core

LINQ

FHIR RESTful API

For the exercise

Git client

Visual Studio 2017

.NET Core 2.0 SDK

SQL Server >= 2012

Postman / Fiddler

Example

• https://github.com/FirelyTeam/Vonk.Facade.Starter

FHIR Facade?

Implementation of a

FHIR RESTful API

as an interface

to an existing

backend system.

Vonk FHIR Facade?

Set of NuGet packages

to build a FHIR Facade

with the ASP.NET (Core)

web stack

(NuGet package = .NET library)

Programming?

• Maximum flexibility

• Fast

• Collect common patterns

• Provide those in other formats

• scripting

• mapping tooling

• code generation

• A growth model

ASP.NET Core

Pipeline of Middleware

Chain of function calls

operating on

HttpContext

Request

Response

ASP.NET Core

Middleware component

(Class with)

Invoke:

function on

HttpRequest

‘next’ (call to next middleware)

public class Middleware { private readonly RequestDelegate _next;

public Middleware(RequestDelegate next)

{ _next = next; }

public async Task Invoke(HttpContext httpContext)

{ // do something on the request await _next(httpContext);

// do something on the response }

}

ASP.NET Core Dependency Injection

• Inversion of Control is key in ASP.NET Core

• Declare your dependencies in your constructor

• Register your services in ConfigureServices()

• Pay attention to scopes

• Transient

• Scoped (Request)

• Singleton

Vonk Pipeline

ASP.NET Core Pipeline with Middleware components

implementing parts of the FHIR RESTful API

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VonkRequest

VonkResponse

Vonk Layered architecture

Pipeline of Middleware

calling Services

by using Repositories

that Map data to and from FHIR

and access the backend

VonkContext

Interface

A bit of Vonk and a touch of your own

VonkContext

Interface

You have

You get

You build

A minimal server

New ASP.Net Core Web Application

Tour of components

• For background

• IVonkContext

• IResource

• IConformanceContributor

• You implement

• ISearchRepository

• IChangeRepository

IVonkContext

Vonk specific ‘HttpContext’ • VonkRequest

• interaction

• resource

• Arguments

• VonkResponse

• responsecode

• resource

• operationoutcome

public interface IVonkContext

{

IVonkRequest Request { get; }

IVonkResponse Response { get; }

IArgumentCollection Arguments { get; }

Uri ServerBase { get; }

string Description { get; }

}

Arguments

Arguments from anywhere

• Path

• QueryString

• Form variables

And you can report issues on them

IResource

Abstraction of Resource

Provides metadata and status

IElementNavigator

for FhirPath navigation

Currently based on POCO

Future: cross-version; invalid resources

interface IResource

{

Navigator { get; }

Type { get; }

Id { get; set; }

Version { get; set; }

LastUpdated { get; set; }

Currency { get; set; }

Change { get; set; }

Contained { get; }

ContainedResources

}

Express your capabilities

Tell what you can do

Contribute to the CapabilityStatement

With IConformanceContributor

Most of this is done for you

Search

Search

Service

My Search Repository My Query

Factory

Query

Context

Q Q Search

CreateQuery

Filter Q

Q

Q

Execute

Map

Arguments

You get the ‘raw’ Arguments

You can control them directly if you must

But usually you relay them...

Search

Service

My Search Repository

Arguments

Querying

Vonk finds out WHAT to query for

id (token)

value (quantity)

name (string)

... and calls Filter

You control HOW you query

SQL

json

http call

... and implement that in Q

My Query Factory

Q Q Q

Query

Context

My Search Repository

Arguments

Filter

Q

Relational

Vonk comes with base classes

for accessing Relational db

with EntityFrameworkCore

and LINQ

ISearchRepository.Search

ISearchRepository - SearchPatient

Provide a

queryfactory

on your entity

type

map the

results

Vonk will Bundle

& serialize

PatientQueryFactory

LINQ on

Patient

Op.Outcome

to do: check

modifiers

Mapping to resource Patient entity

from your db

Create a FHIR

Patient

And populate it

Dependency Injection

Vonk uses ASP.NET Core DI heavily

Register your:

DbContext

SearchRepository

ChangeRepository

ResourceMapper

Reuse

ISearchRepository

can enable

all read-only access:

- read

- vread

- search

- history

- _include, _revinclude

- SMART authorization re

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My SearchRepository

Change

IChangeRepository

can enable

all read-write access:

- create

- update

- delete

- conditional c/u/d (with ISearchRepository)

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My ChangeRepository

Add Validation

Readonly server

Override SearchRepository

+ RelationalQueryFactory

Write a mapping

your model -> FHIR

Startup

AddReadServices()

AddSearchServices()

UseRead()

UseSearch()

Exercise

• Best way to get a feeling for Vonk Facade.... build one!

• Go to http://docs.simplifier.net/vonk/facade/facadestart.html

• Arrange the prerequisites

• Build!

• Find the completed example at: https://github.com/FirelyTeam/Vonk.Facade.Starter

• Find me at the ‘Developer’ table

Sneak preview to Vonk 0.7.0 and Facade

• Server setup and Pipeline of Vonk FHIR Server

• Pick & Choose & Replace

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VonkResponse

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Advantages

• Utilize Vonk Server setup:

• flexible appsettings

• logging

• dependency injection

• application insights

• Focus on your logic

• business

• data access

• Use of Administration API

Configure

Credits

Icons made by several authors from www.flaticon.com