Flutter - Amplify Graphql - Type "Null" is not a subtype of "String" - RESOLVED!! Explanation at the end

Question

I'm getting an error that says `type "Null" is not a subtype of "String". I have no idea where this error is coming from. I can't understand, because It works just fine in amplify studio and it works just fine in AppSync. I'm out of options. Please help! :) I know that I don't have to write graphql query to get a list of activities. But this is the only way to get activityMessages data together because I have a 1:many relationship

For testing, I set a breakpoint where it says final test = await res.response.

Error message

Debugger screenshot

debug_img

AppSync screenshot

Amplify Studio screenshot

It doesn't get to the return

This is my code that throws me an error

   Future<Request<List<Activity?>>> fetchActivitiesByDay(TemporalDate day, String schoolID) async {
    try {
      const listActivities = 'listActivities';
      const graphQLDocument = '''query MyQuery {
  listActivities {
    items {
      id
    end_time
    description
    title
    }
  }
};
      final getPostRequest = GraphQLRequest<Activity>(
        document: graphQLDocument,
        modelType: Activity.classType,
        // variables: <String, String>{'id': 'b34f6dfc-fb18-4f20-85cf-57e97671d480'},
        decodePath: listActivities,
      );
      final res = Amplify.API.query(request: getPostRequest);
      final test = await res.response;
      return formatRequestList<Activity?>(test);
    } on ApiException catch (e) {
      throw e.message;
    }
  }

I've tried without providing a query

const graphQLDocument = '''query {
  listActivities {
    items {
      id
    end_time
    description
    title
    }
  }
};

If I try to get a single activity it works just fine.

const graphQLDocument = '''query GetActivity(\$id: ID!) {
  getActivity(id: \$id) {
    id
  }
};

This is how my schema looks like

type Activity
  @model
  @auth(
    rules: [{ allow: private, operations: [read, update] }, { allow: owner }]
  ) {
  id: ID!
  schoolID: ID!
  category: ActivityEnum!
  title: String!
  start_time: AWSTime!
  end_time: AWSTime!
  date: AWSDate!
  description: String!
  activityMessages: [ActivityMessage]
    @hasMany(indexName: "byActivity", fields: ["id"])
}

type ActivityMessage
  @model
  @auth(rules: [{ allow: private, operations: [read] }, { allow: owner }]) {
  id: ID!
  schoolID: ID!
  activityID: ID! @index(name: "byActivity", sortKeyFields: ["message"])
  activity: Activity! @belongsTo(fields: ["activityID"])
  message: String
  isImage: Boolean!
  imageKey: String
  url: String
  likes: Int!
  createdAt: AWSDateTime
  updatedAt: AWSDateTime
}

EXPLANATION!! The problem was that modelType: Activity.classType is to get single instance. To get a list I had to use modelType: const PaginatedModelType(Activity.classType) and this solved my problem. Working Example

instead of `!` you can use ` ?? ''` to set a default value if the return value is `null`. By that, I think your problem will be solved. — Hamed, May 05 '23 at 03:58

score 0 · Answer 1 · answered May 05 '23 at 04:46

0

I suppose this change will solve your issue:

const graphQLDocument = '''query MyQuery {
  listActivities {
    items {
      id
      end_time
      description
      title
      activityMessages {
        items {
          id
          message
          isImage
          imageKey
          url
          likes
        }
      }
    }
  }
}''';

answered May 05 '23 at 04:46

Hamed

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It didn't work. I still get the same error :/ – Lukas Babaliauskas May 05 '23 at 12:17
Omg.. I solved it :) it works now. I was providing wrong model type. `modelType: Activity.classType` is for a single instance. To get a list I had to use `modelType: const PaginatedModelType(Activity.classType)` – Lukas Babaliauskas May 05 '23 at 13:02

Flutter - Amplify Graphql - Type "Null" is not a subtype of "String" - RESOLVED!! Explanation at the end

1 Answers1