I parked my current build project for a week or two while I did some QA work for a London-based client who had a flutter app built by a small team in Pakistan. Once this was complete I returned to the project only to find it no longer working. It’s a flutter app that uses Environment Agency river data from one of their data.gov.uk apis, and I was certain the only thing that could have changed since I parked the project was the data.

I wasn’t wrong – in my short absence some unexpected data had been added, breaking my mapping from json to model. One of the fields documented by the EA as a string had become in a single record amongst thousands, a list/array.

The documentation:

The data:

I also noticed that the api had become version 0.9 but there was no mention of this in the ‘Recent Updates’ documentation:

The moral of this story is to take the following EA warning seriously:

While they are intended to be stable and robust the open data APIs do not offer a guarantee of service level and should not be relied upon for safety critical applications.

I realised I had to code this more defensively, so in my factory method on the model a try/catch was dropped in, allowing anything consuming this to iterate over bad data but also log it so it can be investigated:

  factory Station.fromJson(Map<String, dynamic> json) {
    try {
      return Station(
        id: json['@id'],
        catchmentName: json['catchmentName'],
        lat: json['lat']?.toDouble(),
        long: json['long']?.toDouble(),
        //etc.....
      );
    } catch (e) {
      throw Exception('Failed to parse fromJson. Station Id:' + json['@id']);
    }
  }
}