Openapi Repository Generator


The aim of this generator is to generate repositories, blocs and freezed models for query params filters for OpenApi module.

openapi-generator-cli is a very powerful tool that allows us to generate client libraries(api calling methods) following Repository pattern, documentation, tests etc for Dart language from the OpenApi/Swagger spec file. A good can be this article on how to generate OpenApi client library from OpenApi/Swagger specification Article Link

But generated client library containing OpenApi endpoints is not very efficient to use with pagination or filtering data. Here list_bloc comes into play. It utilizes the Bloc library to create DataCubit, ListCubit state management solution. Which supports pagination and filtering data for the generated endpoints. And help us remove a lot boilerplate codes to support pagination and filtering.

And our openapi_repository library takes that to even further. It is possible to provide those endpoints, it will automatically generate DataCubit and ListCubit which can be easily used to with widgets provided in list_bloc and flutter_list_bloc

It will create generate Repository like this with relevant methods


Make sure you've generated OpenApi client library using OpenApi(Swagger) schema definitions and openapi-generator-cli. And make sure that each operationId in the OpenApi(Swagger) schema has operations(create, update, partial_update, retrieve, destroy, list etc) suffix which helps the library to detect methods. For each CRUD operations it also checks api call method. (retrieve -> GET, list -> GET, create -> POST, update -> PUT, partial_update -> PATCH, destroy -> DELETE)

Then create a flutter/dart project. Make sure previously generated(using openapi-generator-cli) OpenApi client library can be imported in the flutter/dart project. Then install these depdencies

For Flutter:

flutter pub add openapi_repository_annotations
flutter pub add list_bloc
flutter pub add flutter_list_bloc
flutter pub add dio
flutter pub add openapi_repository --dev
flutter pub add build_runner --dev
flutter pub add built_value_generator --dev

For Dart:

dart pub add openapi_repository_annotations
dart pub add list_bloc
dart pub add flutter_list_bloc
dart pub add dio
dart pub add openapi_repository --dev
dart pub add build_runner --dev
dart pub add built_value_generator --dev

Use @OpenapiRepository annotation on the class that will hold the generated files. Use annoation params to configure how the files should be generated. Example: Annotation Usage

Here $ApiRepository class will holding the generated files in part 'api_repository.openapi.dart'; part 'api_repository.freezed.dart'; part 'api_repository.g.dart'; directories. This generator will add files to part 'api_repository.openapi.dart'; first.

After adding annotation run flutter pub run build_runner build --delete-conflicting-outputs or dart run build_runner build --delete-conflicting-outputs

This should generate Repository, DataBlocs, ListBlocs in the same directory as the $ApiRepository class.

Generated ApiRepository class will look something like this

class ApiRepository {
  static ApiRepository get instance => _instance;
  static final ApiRepository _instance = ApiRepository._internal();

  ApiRepository._internal() {
      ..baseUrl = sandboxBasePath
      ..connectTimeout = 3000
      ..receiveTimeout = 5000
      ..sendTimeout = 3000;

  static const String liveBasePath = '';
  static const String sandboxBasePath = '';

  void updateBaseUrl(String baseUrl) {
    _openapi.dio.options.baseUrl = baseUrl;

  static final Openapi _openapi = Openapi(
    basePathOverride: kReleaseMode ? liveBasePath : null,
    interceptors: [],

  Openapi get api => _openapi;
  PetApi get pet => api.getPetApi();
  StoreApi get store => api.getStoreApi();
  UserApi get user => api.getUserApi();

And Generated Repository from endpoints will look like something like this

abstract class PetRepository {
  static Future<Pet> retrieve([
    PetRetrieveFilter? filter,
  ]) async {
    if (filter == null) {
      throw Exception('Invalid filter');
    final r = await
      petId: filter.petId,
    if ( == null) {
      throw Exception('Failed to load data!');
    } else {

  Future<void> create({
    required Pet body,
  }) async {

And ListBloc and DataBloc with relevant methods extending the generated Repository like PetRepository will be generated as well.

class PetDataBloc extends DataCubit<Pet, PetRetrieveFilter> with PetRepository {
    Future<Pet> Function([
      PetRetrieveFilter? filter,
  ) : super(PetRepository.retrieve);

  Future<void> create({
    required Pet body,
  }) async {
    final r = await super.create(
      body: body,

    return r;

And we can directly use this piece of PetDataBloc with widgets from flutter_list_bloc


DataBlocBuilder<PetDataBloc, Pet, PetRetrieveFilter>(
  create: (context) => PetDataBloc(PetRepository.retrieve)
      PetRetrieveFilter(petId: widget.petId),
  emptyBuilder: (_, __) => const Center(
    child: Text('No data'),
  loadingBuilder: (_, __) => const Center(
    child: CircularProgressIndicator(),
  itemBuilder: (context, state) => .........

For full example: Example generated files

How this library works

This library uses annotation(@OpenapiRepository) on a class. This annonated class will hold all the generated Repository, DataBlocs, ListBlocs. It searches for {methodPrefix}Retrieve/List (where request api call method is also GET) and then finds relevant {methodPrefix}Update/PartialUpdate/Destroy/{randomMethod sufix} and put them inside annotated class in Repository pattern. Based on the generated class from annotation it will generate DataBlocs(for {methodPrefix}Retrieve) and ListBlocs(for {methodPrefix}List) and these Blocs will inherite other methods inside the generated class. These Blocs can be directly used with flutter_list_bloc or list_bloc widgets.


Tutorials for code generation from annotation

To learn more about code generation using annotation:


A package called openapi_repository_annotations is created to hold all annotations. This will be added as a dependency module in the projects, while the generator itself will be a dev-dependency.

For the purpose of this project, we have created an annotation called @OpenapiRepository() which can also be invoked with @openApiRepository. The annotation must be have a const constructor for it to be used as a subtype for GeneratorForAnnotation.

@OpenapiRepository() Takes multiple values

  • Type buildFor : The main OpenApi class which contains all the API Objects(which are used to fetch Api methods for each API Object. Ex: OpenApi -> AccountsApi -> {AccountsApi related API methods}).
  • List<RepositoryBuilder> builderList : It helps to pass allowed/ingorable methods for a API class object. RepositoryBuilder contains List of allowed and ingorable api method names. if the value is * then all will be counted for allowed/ingorable for that method. For example: We can pass RepositoryBuilder(AccountsApi, allowedEndpoints: [*], ignoreEndpoints = []) then it will generate for all the endpoints that is included inside AccountsApi class and ingore none of the endpoints.
  • List<BlocMixin> blocMixins : It helps to pass BlocMixins which hold a dart mixin element. Generated ListBloc/DataBloc will use the provided mixins.
  • int connectTimeout : timeout for the connecting with the server. Default: 10000
  • int receiveTimeout : timeout for to receive data from server. Default: 15000
  • int sendTimeout : timeout to send/upload data to the server. Default: 15000
  • int defaultOffset : Default offset for paginated APIs. Default: 0
  • int defaultPageSize : Default pagesize/limit for paginated APIs. Default: 100
  • Type? dioInterceptor : Includable DioInterceptor
  • String? liveBasePath : Includable baseUrl for liveMode(kReleaseMode) which will override the default baseUrl in liveMode.
  • String? baseUrl : Includable baseUrl which will be used for default baseUrl for Dio configuration

For example please follow this link: Annotation Usage

This will generate Filter, DataCubit, ListCubit, Repository classes with Dio configuration.

Generated files will in {fileName}.openapi.dart.

For generated example file please follow this link: Generated Classes


The generator code is available in lib/src/list_repository_generator.dart For this use case we went ahead with GeneratorForAnnotation so that we can create an Annotation that we can use to mark classes on which the generator is supposed to run on.

Any class which extends from GeneratorForAnnotation should override the generateForAnnotatedElement method. This method should return a String, which is passed out as the output for the generator.

For e.g.

class OpenapiRepositoryGenerator extends GeneratorForAnnotation<OpenapiRepository> {

    String generateForAnnotatedElement(
        Element element,
        ConstantReader annotation,
        BuildStep buildStep,
    ) {
        return '// Output';

The above code block will generate a file with an output similar to the below block.


part of 'xxxxxxxxxxxx.dart';

// **************************************************************************
// xxxxxxxxxxxxxxxxGenerator
// **************************************************************************

// Output

The most important of the generateForAnnotatedElement method is the Element argument, which provides details on the Class/method/function/type that the annotation was placed on. Using the element we can get more insights on whether the element is static, or private, etc. Additionally it is possible to peek into the Element and get more data on it's child elements as well. This can be done by creating an instance of an ElementVisitor and using element.visitChildren(vistor).


To take a peek into the inner fields or parameters or property accessors, etc, we need to define a class which extends from SimpleElementVisitor. In this project, this is done at model_visitor.dart where 2 instances of SimpleElementVisitors are created.


This method is created to perform the following steps

  1. Iterate over all methods in a class.
  2. For every method in the class, check if the return type is Future<T> such that
    • T is either an instance of List or BuiltList for List method, or any object for Retrieve method OR
    • For List method, T has a parameter called results such that results is an instance of List or BuiltList. This happens when the API returns a paginated response. To acheive this another visitor called InlineClassVisitor is used.
  3. If 2 is satisfied, the required data is parsed into a class called RepositoryModel and saved in the listMethods field of the visitor which can then be accessed from the calling Element.


This class helps to find the api call type(PUT, POST, DELETE etc) of an method.


The builder defines the type of builder to use. In the case of this project a PartBuilder is used.

Builder generateListRepository(BuilderOptions options) => PartBuilder(

We have to define here what the part declaration needs to be. In this case we went ahead with .query.dart.

We cannot use a SharedPartBuilder as of now because, the code that is generated also creates @freezed annotations. There are a few issues created related to this which suggested to go ahead with PartBuilder


This is the file which tells builder how to build the code

        enabled: true

    target: ":generators"
    import: "package:openapi_repository/openapi_repository.dart"
    builder_factories: ["generateListRepository"]
    build_extensions: { ".dart": [".g.dart"] }
    auto_apply: dependents
    runs_before: [freezed_annotations|freezed_annotations]
    build_to: source # Tells builder to generate file to the same path of the file where annotation was created and not to the default .dart_tool/build/generated/ path.
    applies_builders: ["source_gen|combining_builder"]