getRelation with error: Invalid Relation key name

[catalunha]

I'm building a tutorial for Parse Serve (using Back4app) and ran into this issue on SKD for Flutter.

New Issue Checklist

• [x ] I am not disclosing a vulnerability.
• [ x] I am not just asking a question.
• [ x] I have searched through existing issues.
• [x ] I can reproduce the issue with the latest version of Parse Server and the Parse Flutter SDK.

Issue Description

I tested the following code. All very well.

    log('addRelation 01');
    final parseObjectBook01 = ParseObject(BookEntity.className);
    parseObjectBook01.objectId = 'aeOTTuGO7r';
    final parseObjectAuthor01 = ParseObject(AuthorEntity.className);
    parseObjectAuthor01.objectId = 'fK4I00NlBy';
    parseObjectBook01.addRelation('typeRelationAuthor', [parseObjectAuthor01]);
    await parseObjectBook01.save();

But this code. It generates error. Informed below.

    log('addRelation 01a');
    final parseObjectBook01 = ParseObject(BookEntity.className);
    parseObjectBook01.objectId = 'aeOTTuGO7r';
    var parseRelationBook = parseObjectBook01.getRelation('typeRelationAuthor');
    final parseObjectAuthor01 = ParseObject(AuthorEntity.className);
    parseObjectAuthor01.objectId = 'fK4I00NlBy';
    parseRelationBook.add(parseObjectAuthor01);
    await parseObjectBook01.save();

Exactly on this line:
var parseRelationBook = parseObjectBook01.getRelation('typeRelationAuthor');

Steps to reproduce

Create a pure standard Dart project with VSCode
Create a basic project in back4app and write down the appId and clientKey.
Copy the code above to your Dart project and enter the correct appId and clientKey and then a wrong value.
Run the Dart project with:
$ dart bin/learning_about_b4a_dart.dart

Actual Outcome

Error

Expected Outcome

May the result be the same. In both codes

Environment

Parse Flutter SDK

• SDK version: parse_server_sdk_flutter: ^3.1.3
• Operating system version: Description: Pop!_OS 22.04 LTS

Server

• Parse Server version: 4.5.0

Logs

Connecting to VM Service at http://127.0.0.1:35555/jjn-YZQ6Y-s=/
[log] Back4app Connected.
[log] addRelation 01a
Unhandled exception:
Invalid Relation key name
#0 new ParseRelation
package:parse_server_sdk/…/objects/parse_relation.dart:7
#1 ParseObject.getRelation
package:parse_server_sdk/…/objects/parse_object.dart:313
#2 BookAddData.addRelations2
package:learning_about_b4a_dart/…/book/book_add_data.dart:108
#3 main
bin/learning_about_b4a_dart.dart:81

Exited (255)

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[catalunha]

Congratulations and thanks @mtrezza ,
I wish I had more knowledge to solve issues and not just create them.
I'm struggling here.

[mbfakourii]

You have created an empty parseObject and you are trying to get the value but your key does not exist in the empty ParseObject ! I suggest first fetch and next try getRelation. like this

var parseObjectBook01 = ParseObject(BookEntity.className);
parseObjectBook01.objectId = 'aeOTTuGO7r';
parseObjectBook01 = await parseObjectBook01.fetch(); // <--------
var parseRelationBook = parseObjectBook01.getRelation('typeRelationAuthor');

[catalunha]

It is true @mbfakourii
Sorry for the inconvenience and thanks for the help.
I thought that only for addition it made association and allowed addition.

[catalunha]

Final code follows.

  static addRelations() async {
    log('addRelation 01');
    //The downside of this approach is that it fetches the data.
    var parseObjectBook01 = ParseObject(BookEntity.className);
    parseObjectBook01.objectId = 'aeOTTuGO7r';
    parseObjectBook01 = await parseObjectBook01.fetch();
    var parseRelationBook = parseObjectBook01.getRelation('typeRelationAuthor');
    print(parseRelationBook.toJson());
    print(parseRelationBook.toString());
    final parseObjectAuthor01 = ParseObject(AuthorEntity.className);
    parseObjectAuthor01.objectId = 'fK4I00NlBy';
    parseRelationBook.add(parseObjectAuthor01);
    await parseObjectBook01.save();

    log('addRelation 02');
    final parseObjectBook02 = ParseObject(BookEntity.className);
    parseObjectBook02.objectId = 'gkotvO6IKI';
    final parseObjectAuthor02 = ParseObject(AuthorEntity.className);
    parseObjectAuthor02.objectId = 'ETwKYOAMh2';
    parseObjectBook02.addRelation(
        'typeRelationAuthor', [parseObjectAuthor01, parseObjectAuthor02]);
    await parseObjectBook02.save();
  }