Manageprovidercommand

Mixin Implementation

// lib/shared/providers/command_provider_base_mixin.dart
import 'package:odu_core/odu_core.dart';
import 'package:riverpod_annotation/riverpod_annotation.dart';

AsyncValue<T> invalidState<T>() => AsyncError<T>(
  StateError('Not called yet'),
  StackTrace.current,
);

mixin CommandMixin<T> on $Notifier<AsyncValue<T>> {
  Result<T> emitError<E extends Exception>(E error, [StackTrace? stackTrace]) {
    if (ref.mounted) {
      state = AsyncError(error, stackTrace ?? StackTrace.current);
    }
    return Err(error, stackTrace ?? StackTrace.current);
  }

  Result<T> emitData(T data) {
    if (ref.mounted) {
      state = AsyncData(data);
    }
    return Ok(data);
  }

  void emitLoading() {
    if (ref.mounted) {
      state = const AsyncLoading();
    }
  }

  Result<T> emitResult(Result<T> result, [StackTrace? stackTrace]) {
    if (ref.mounted) {
      state = switch (result) {
        Ok<T>(value: final data) => AsyncData(data),
        Err<T>(value: final error) => AsyncError(
          error,
          stackTrace ?? StackTrace.current,
        ),
      };
    }
    return result;
  }
}

Structure

@riverpod
class AddExercise extends _$AddExercise with CommandMixin<Exercise> {
  @override
  AsyncValue<Exercise> build() {
    return invalidState();
  }

  Future<void> call(DailyTraining training, Exercise exercise) async {
    emitLoading();
    final repository = ref.read(trainingRepositoryProvider);
    training.addExercise(exercise);
    final result = await repository.store(training).map((_) => exercise);
    emitResult(result);
  }
}

Naming Conventions

Return Types

Future<void> - Fire and Forget

Future<void> call(DailyTraining training, Exercise exercise) async {
  emitLoading();
  final result = await repository.store(training).map((_) => exercise);
  emitResult(result);
}

FutureResult<T> - Caller Needs Result

FutureResult<Exercise> call(
  DailyTraining training, {
  required PositionedExercise exercise,
}) async {
  emitLoading();
  training.setExercise(exercise);
  final result = await ref
      .read(trainingRepositoryProvider)
      .store(training)
      .map((_) => exercise.value);
  return emitResult(result);
}

Command with Unit Return Type

@riverpod
class MergeExercises extends _$MergeExercises with CommandMixin<Unit> {
  @override
  AsyncValue<Unit> build() => invalidState();

  Future<void> call(
    DailyTraining training, {
    required List<PositionedExercise> exercises,
  }) async {
    emitLoading();
    training.mergeExercises(exercises);
    final result = await ref
        .read(trainingRepositoryProvider)
        .store(training)
        .map((_) => unit);
    emitResult(result);
  }
}

Maintenance and Modification

When modifying existing commands:

1. Preserve State Logic: Ensure emitLoading() is called at the start and emitResult() (or equivalent) at the end.
2. Update Parameters: If changing the call method signature, ensure all call sites are updated.
3. Refactor Responsibilities: If a command is growing too large or handling multiple distinct actions, split it into separate command providers.
4. Check Dependencies: When adding new dependencies (e.g., a new repository), use ref.read() within the call method, not ref.watch().

Anti-Patterns

❌ Business Logic in Provider

// BAD: Validation belongs in entity
Future<void> call(DailyTraining training, Exercise exercise) async {
  if (exercise.name.isEmpty) {
    emitError(ValidationException('Name required'));
    return;
  }
  // ...
}

❌ Multiple Responsibilities

// BAD: One action per provider
class ExerciseManager extends _$ExerciseManager with CommandMixin<void> {
  Future<void> add(...) async { ... }
  Future<void> update(...) async { ... }
  Future<void> delete(...) async { ... }
}

❌ Command Without CommandMixin

// BAD: Missing mixin and invalidState()
class AddExercise extends _$AddExercise {
  @override
  AsyncValue<Exercise> build() => AsyncData(Exercise.empty());
}

❌ Manual State Switching

// BAD: Use emitResult() instead
state = switch (result) {
  Ok() => AsyncData(exercise),
  Err(value: final err) => AsyncError(err, StackTrace.current),
};

Code Smells

Code Generation

import 'package:riverpod_annotation/riverpod_annotation.dart';

part 'your_command.g.dart';

dart run build_runner build -d