jomg 0.0.3-dev

A build package to generate Dart objects models from one or more JSON definitions.

JOMG

The Json Object Model Generator is an opinionated builder designed to convert 1 or more json definitions into a set of class based object models. It does this by analysing the JSON and attempting to create a representation of the JSON as Dart classes.

Features

JOMG will create a set of 1 or more Dart models from each .json file that it finds in the defined src_dir, the number of generated classes will depend on how complex the JSON is. These files are created (or overwritten) to the defined output_dir.

Installation

JOMG is intended for use when developing Dart/Flutter project so it should be installed in the dev_dependencies section of your projects pubspec.yaml file

dev_dependencies:
  jomg:

Then at the top level of your pubspec.yaml add entries to define the src_dir and output_dir directories, PLEASE NOTE these directories must exist. See below for an example entry, or look in the pubspec.yaml in the /example directory.

jomg:
  src_dir: 'src/json'
  output_dir: 'lib/src/models'
  all_attributes_required: false

There is a third configuration option all_attributes_required. This is optional and is only required if you wish all the attributes generated in a model to be required. By default all are set to optional so they can be null if needed, this is done as the model does not know which attributes in the JSON are always present and which are not (its is simpler, and safer, to assume they can all be null).

Conversion rules

• The name of the dart file created is {json file name}_model.dart
• The name of the object created is {json file name}Model
• Any complex types in the json will have there own models created (Dart List and Map types)
• Any sub models are named using the JSON attribute name i.e. {json attribute}_model.dart and {json attribute name}Model

Known Limitations

The JSON must be well formed and not contain complex types of the same name with varying structures. For example

{
  "question": "How long is a piece of string?",
  "answers": [
    {"order": 1, "answer": "Too long"},
    {"order": 2, "answer": "Too short"},
    {"order": 3, "answer": "Who cares"},
    {"order": 4, "answer": "Stupid question"}
  ],
  "help":{
    "title": "hints"
    "answers": [
        {"id": 1, "description": "Always reply with answer 4"},
        {"id": 1, "description": "Answer 3 is the best bet"}
    ]
  }
}

This has 2 Lists defined both named answers, but they are NOT the same object as they have a different structure which will mean the JOMG will overwrite any AnswersModel generated only with the last one found. The solution would be to change the attribute name of one, for example the answers in the help structure could be called help_answers.

Usage

Just run the flutter packages pub run jomg command in the root of your project to start the generator process, and create the models from the JSON found.

For example a simple object defined in a file called entry.json:

{
  "id": 1,
  "name": "Test Entry"
}

would be converted as entry_model.dart to

class EntryModel {
  final int? id;
  final String? fullName;
  
  EntryModel(this.id, this.fullNname);

  static EntryModel fromJson(Map<String, dynamic> json) {
    return EntryModel(
      id: json['id'],
      fullName: json['full_name']
    );
  }
}

For a more in-depth example that generates multiple objects from a single JSON file see the /example folder. This example also shows the automated creation of static fromJson methods to import the JSON data directory into the Object Model.

Additional information

This is currently an experimental package, originally created as a private builder for generating Dart objects that can be used to track the data returned from APIs. I have released it to see if it is helpful to anyone else.