firebase - 将 Flutter 对象与列表映射到 Firebase 实时数据库

Question

我正在尝试将我的轮询对象保存到 Firebase 实时数据库，但我真的不知道如何使用我的轮询对象执行此操作，因为它有一个列表。我试图找到一个教程，如何将带有 map 的对象映射到 firebase，但没有找到任何内容。

class Poll {
  String id;
  String name;
  String description;
  List<Question> questions;

  Poll({this.name, this.description, this.questions});

  Poll.fromSnapshot(DataSnapshot snapshot) {
    id = snapshot.key;
    name = snapshot.value['name'];
    description = snapshot.value['description'];
    questions = snapshot.value['questions'];
  }

  toJson() {
    return {'name': name, 'description': description, 'questions': questions};
  }
}

class Question {
  String id;
  String question;
  String customAnswer;

  Question.customAnswer({this.question, this.customAnswer});

  Question.fromSnapshot(DataSnapshot snapshot) {
    id = snapshot.key;
    question = snapshot.value['question'];
    customAnswer = snapshot.value['customAnswer'];
  }

  toJson() {
    return {'question': question, 'customAnswer': customAnswer};
  }
}

这里我尝试写入数据库:

RaisedButton(
                onPressed: () async {
                  Poll poll1 =
                      Poll(name: 'poll1', description: 'desc1', questions: [
                    Question.customAnswer(
                        question: 'who am i', customAnswer: 'Ostap'),
                    Question.customAnswer(
                        question: 'who are you', customAnswer: 'test'),
                  ]);
                  await databaseReference
                      .child('Polls')
                      .push()
                      .set(poll1.toJson());
                },
                child: Text('Write To DB'),

这里出现错误:

Exception has occurred.
ArgumentError (Invalid argument: Instance of 'Question')

其原因是 await databaseReference

有人可以帮助我吗？提前致谢!

Answer 1

我已经根据您的代码创建了一个 JSON

{
  "id":"",
  "name":"",
  "description":"",
  "questions": [
      {
        "id":"",
        "question":"",
        "customAnswer":""
      }
  ]
}

然后生成 dart 类 Use this website 。你的对象类将如下所示。

class Welcome {
Welcome({
    this.id,
    this.name,
    this.description,
    this.questions,
});

String id;
String name;
String description;
List<Question> questions;

factory Welcome.fromJson(Map<String, dynamic> json) => Welcome(
    id: json["id"],
    name: json["name"],
    description: json["description"],
    questions: List<Question>.from(json["questions"].map((x) => Question.fromJson(x))),
);

Map<String, dynamic> toJson() => {
    "id": id,
    "name": name,
    "description": description,
    "questions": List<dynamic>.from(questions.map((x) => x.toJson())),
};

}

class Question {
Question({
    this.id,
    this.question,
    this.customAnswer,
});

String id;
String question;
String customAnswer;

factory Question.fromJson(Map<String, dynamic> json) => Question(
    id: json["id"],
    question: json["question"],
    customAnswer: json["customAnswer"],
);

Map<String, dynamic> toJson() => {
    "id": id,
    "question": question,
    "customAnswer": customAnswer,
};

}

现在您将能够调用 await ...set(poll1.toJson()); 而不会出现任何错误