Instance Of 'JSArray<dynamic>': Type 'List<dynamic>' Is Not A Subtype Of Type 'Map<String, Dynamic>'

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Introduction

When working with data serialization and deserialization in Dart, using libraries like freezed can simplify the process. However, sometimes, you may encounter errors that can be frustrating to resolve. In this article, we will explore a specific issue related to the freezed library and how to resolve it.

Describe the Bug

The issue at hand is related to the freezed library version 2.5.7 and its usage in a web application. The error message indicates that there is a type mismatch between List<dynamic> and Map<String, dynamic>. This error occurs when trying to parse a JSON object into a specific data model.

To Reproduce

To reproduce this issue, let's consider two models: SessionFeedback and FeedbackDetails. These models are defined using the freezed library.

@Freezed(makeCollectionsUnmodifiable: false)
class SessionFeedback with _$SessionFeedback {
  const factory SessionFeedback({
    required String id,
    required String playerUid,
    required String trainerUid,
    required String sessionId,
    required DateTime createdAt,
    required FeedbackDetails feedbackDetails,
    required List<FeedbackConversation> conversation,
    String? notes,
  }) = _SessionFeedback;

  factory SessionFeedback.fromJson(Map<String, Object?> json) =>
      _$SessionFeedbackFromJson(json);

  /// Setup default values for the session feedback firebase document
  static Map<String, dynamic> get defaultValues => {
    'createdAt': DateTime.now().toIso8601String(),
    'conversations': [],
  };
}

@freezed
class FeedbackDetails with _$FeedbackDetails {
  const factory FeedbackDetails({
    required Mindset mindset,
    required Receptivity receptivity,
    required Engagement engagement,
    required Understanding understanding,
  }) = _FeedbackDetails;

  factory FeedbackDetails.fromJson(Map<String, Object?> json) =>
      _$FeedbackDetailsFromJson(json);
}

The SessionFeedback model has a feedbackDetails property of type FeedbackDetails, which is an enum-based model. The FeedbackDetails model has four properties: mindset, receptivity, engagement, and understanding, all of which are enums.

Expected Behavior

The expected behavior is that the parsing should work as it does in the mobile app, where the same model classes are used. However, the error occurs at the fromJson implementation of the SessionFeedback model.

_$SessionFeedbackImpl _$SessionFeedbackImplFromJson(
        Map<String, dynamic> json) =>
    _$SessionFeedbackImpl(
      id: json['id'] as String,
      playerUid: json['playerUid'] as String,
      trainerUid: json['trainerUid'] as String,
      sessionId: json['sessionId'] as String,
      createdAt: DateTime.parse(json['createdAt'] as String),
      feedbackDetails: FeedbackDetails.fromJson(
          json['feedbackDetails'] as Map<String, dynamic>), // <-- here
      conversation: (json['conversation'] as List<dynamic>)
          .map((e) => FeedbackConversation.fromJson(e as Map<String, dynamic>))
          .toList(),
      notes: json['notes'] as String?,
    );

Resolving the Issue

The issue arises from the fact that the feedbackDetails property in the SessionFeedback model is of type FeedbackDetails, which is an enum-based model. However, in the fromJson implementation, we are trying to parse a Map<String, dynamic> into a FeedbackDetails object.

To resolve this issue, we need to modify the fromJson implementation of the SessionFeedback model to correctly parse the feedbackDetails property. We can do this by using the fromJson method of the FeedbackDetails model to parse the feedbackDetails property.

_$SessionFeedbackImpl _$SessionFeedbackImplFromJson(
        Map<String, dynamic> json) =>
    _$SessionFeedbackImpl(
      id: json['id'] as String,
      playerUid: json['playerUid'] as String,
      trainerUid: json['trainerUid'] as String,
      sessionId: json['sessionId'] as String,
      createdAt: DateTime.parse(json['createdAt'] as String),
      feedbackDetails: FeedbackDetails.fromJson(
          json['feedbackDetails'] as Map<String, dynamic>), // <-- here
      conversation: (json['conversation'] as List<dynamic>)
          .map((e) => FeedbackConversation.fromJson(e as Map<String, dynamic>))
          .toList(),
      notes: json['notes'] as String?,
    );

However, this will not work because the feedbackDetails property is not a Map<String, dynamic>. It is an enum-based model. To resolve this issue, we need to modify the fromJson implementation of the SessionFeedback model to correctly parse the feedbackDetails property.

_$SessionFeedbackImpl _$SessionFeedbackImplFromJson(
        Map<String, dynamic> json) =>
    _$SessionFeedbackImpl(
      id: json['id'] as String,
      playerUid: json['playerUid'] as String,
      trainerUid: json['trainerUid'] as String,
      sessionId: json['sessionId'] as String,
      createdAt: DateTime.parse(json['createdAt'] as String),
      feedbackDetails: FeedbackDetails(
        mindset: Mindset.values[json['feedbackDetails']['mindset'] as int],
        receptivity: Receptivity.values[json['feedbackDetails']['receptivity'] as int],
        engagement: Engagement.values[json['feedbackDetails']['engagement'] as int],
        understanding: Understanding.values[json['feedbackDetails']['understanding'] as int],
      ),
      conversation: (json['conversation'] as List<dynamic>)
          .map((e) => FeedbackConversation.fromJson(e as Map<String, dynamic>))
          .toList(),
      notes: json['notes'] as String?,
    );

In this modified implementation, we are using the values property of the enum to parse the feedbackDetails property.

Conclusion

In conclusion, the issue of Instance of 'JSArray<dynamic>': type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>' can be resolved by modifying the fromJson implementation of the SessionFeedback model to correctly parse the feedbackDetails property. This can be done by using the values property of the enum to parse the feedbackDetails property.

Additional Tips

  • When working with data serialization and deserialization in Dart, it is essential to understand the types and structures of the data being serialized and deserialized.
  • The freezed library can simplify the process of data serialization and deserialization in Dart, but it requires careful consideration of the types and structures of the data being serialized and deserialized.
  • When encountering errors related to type mismatches, it is essential to carefully examine the types and structures of the data being serialized and deserialized to resolve the issue.

References

  • Freezed Library
  • Dart Documentation
    Instance of 'JSArray': type 'List' is not a subtype of type 'Map<String, dynamic>' ===========================================================

Q&A

Q: What is the issue with the freezed library in this scenario? A: The issue is that the freezed library is trying to parse a List<dynamic> into a Map<String, dynamic>, which is not a valid type conversion.

Q: Why is this issue occurring? A: This issue is occurring because the fromJson implementation of the SessionFeedback model is trying to parse a List<dynamic> into a Map<String, dynamic>, which is not a valid type conversion.

Q: How can I resolve this issue? A: To resolve this issue, you need to modify the fromJson implementation of the SessionFeedback model to correctly parse the feedbackDetails property. You can do this by using the values property of the enum to parse the feedbackDetails property.

Q: What is the correct way to parse the feedbackDetails property? A: The correct way to parse the feedbackDetails property is to use the values property of the enum to parse the feedbackDetails property. For example:

feedbackDetails: FeedbackDetails(
  mindset: Mindset.values[json['feedbackDetails']['mindset'] as int],
  receptivity: Receptivity.values[json['feedbackDetails']['receptivity'] as int],
  engagement: Engagement.values[json['feedbackDetails']['engagement'] as int],
  understanding: Understanding.values[json['feedbackDetails']['understanding'] as int],
),

Q: What are some additional tips for working with data serialization and deserialization in Dart? A: Some additional tips for working with data serialization and deserialization in Dart include:

  • Understanding the types and structures of the data being serialized and deserialized.
  • Using the freezed library to simplify the process of data serialization and deserialization.
  • Carefully examining the types and structures of the data being serialized and deserialized to resolve any issues that may arise.

Q: What are some common issues that can occur when working with data serialization and deserialization in Dart? A: Some common issues that can occur when working with data serialization and deserialization in Dart include:

  • Type mismatches between the data being serialized and deserialized.
  • Issues with the structure of the data being serialized and deserialized.
  • Problems with the serialization and deserialization process itself.

Q: How can I troubleshoot issues with data serialization and deserialization in Dart? A: To troubleshoot issues with data serialization and deserialization in Dart, you can:

  • Carefully examine the types and structures of the data being serialized and deserialized.
  • Use the freezed library to simplify the process of data serialization and deserialization.
  • Use debugging tools to identify and resolve any issues that may arise.

Q: What are some best practices for working with data serialization and deserialization in Dart? A: Some best practices for working with data serialization and deserialization in Dart include:

  • Understanding the types and structures of the data being serialized and deserialized.
  • Using the freezed library simplify the process of data serialization and deserialization.
  • Carefully examining the types and structures of the data being serialized and deserialized to resolve any issues that may arise.

Conclusion

In conclusion, the issue of Instance of 'JSArray<dynamic>': type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>' can be resolved by modifying the fromJson implementation of the SessionFeedback model to correctly parse the feedbackDetails property. This can be done by using the values property of the enum to parse the feedbackDetails property. Additionally, some best practices for working with data serialization and deserialization in Dart include understanding the types and structures of the data being serialized and deserialized, using the freezed library to simplify the process, and carefully examining the types and structures of the data being serialized and deserialized to resolve any issues that may arise.