Flutter firebase 从文档中获取一个字段

Question

I'm trying to get the message from a field in a collection. It is a read only data, i have modeled it like this

class SocialShare {
  final String message;
  SocialShare({
    this.message,
  });
  factory SocialShare.fromJson(Map<String, dynamic> json) {
    return SocialShare(
      message: json['message'],
    );
  }
}

I have a collection named 'Social Share and contains a doc with a single field called message..

Here is how i call it

class SocialShares {
  final CollectionReference _socialMessage =
      FirebaseFirestore.instance.collection('socialShare');

  Future<SocialShare> fetchsocial() {
    return _socialMessage.get().then((value) {
      return SocialShare.fromJson(value); // how can i call it
    });
  }
}

How can i get a that value from firebase

Answer 1

You can do fetchSocial async and await the result to return:

fetchSocial() async{
  var value = await _socialMessage.get();
  return SocialShare.fromJson(value);
}

then you have to call fetchSocial method with await or then where you need it.

await fetchSocial() or fetchSocial.then...

Answer 2

The value in _socialMessage.get().then((value) { is a QuerySnapshot object , which contains the DocumentSnapshot s of all documents in the socialShare collection.

To get a field, or the Map<String, dynamic> of all fields, you need the data from a single document. For example, to get the message field fro the first document from the collection, you can do:

return SocialShare.fromJson(value.docs[0].data());