Services

How to use a few different services hidden away in the app template library.

On this page:

Person lookup

The person lookup service can be use to verify a national identity number and to retrieve person information about the identified person. The user will need to provide the national identity number and the last name of the person. The service will then verify the input by comparing it with stored data. Both input are required and the last name is used to prevent cleaning of random identity numbers. If the user inputs invalid data too many times the service will block the user for some time.

The returned person data can be used to populate additional fields in the model.

Person lookup example

The service can be used in any of the handlers in the logic namespace. Below we’ve created an example using the ProcessDataWrite method in DataProcessingHandler.

public async Task<bool> ProcessDataWrite(
    Instance instance, Guid? dataId, object data)
{
    if (data is MessageV1 message)
    {
        Person person = await _personLookup.GetPerson(
            message.Personnummer, 
            message.Etternavn, 
            CancellationToken.None);

        message.Fornavn = person.FirstName;
        return true;
    }

    return false;
}

For this to work we’ll need to do a few other changes in DataProcessingHandler.

Add a private field for the lookup service and change the constructor to take an instance of the service. Initialize the field in the body of the constructor.

private readonly IPersonLookup _personLookup;

public DataProcessingHandler(IPersonLookup personLookup)
{
    _personLookup = personLookup;
}

The changes to the DataProcessingHandler constructor also force us to update the constructor call from the App class constructor. Add IPersonLookup as an input parameter and use the parameter value as input to the constructor of DataProcessingHandler.

public App(
    ...
    IText textService,
    IPersonLookup personLookup,
    IHttpContextAccessor httpContextAccessor) : base(...)
{
    _logger = logger;
    _validationHandler = new ValidationHandler(httpContextAccessor);
    _dataProcessingHandler = new DataProcessingHandler(personLookup);
    _instantiationHandler = new InstantiationHandler(profileService, registerService);
    _pdfHandler = new PdfHandler();
}

A note on exception handling

With no other changes than those above, the app backend will return response code 429 - TooManyRequests if the user has been typing in invalid data too many times. This response code is currently not handled by the frontend react application which results in an “unknown error”. This can be avoided with exception handling that singles out any PlatformHttpException with a response with status code 429, but there are currently no built in mechanism to convey to the user why a request failed. A workaround for this limitation is to use a property on the data model.

try
{
    ...
    return true;
}
catch (PlatformHttpException phex)
{
    switch (phex.Response.StatusCode)
    {
        case HttpStatusCode.TooManyRequests:
            // Add corrective messures
            break;
        case HttpStatusCode.NotFound:
            // Add corrective messures
            break;
    }
    throw;
}