如何从refrenced文档（Firebase）中的字段获取String数据

Question

In my Flutter Application I would like to get some information from a field which contains a refrence to another Collection. I don't know how to get to the information from the field inside the referenced document.

Down below are two pictures of both collections.

The first picture contains the main collection where the field ("geslacht") refers to: "/gender/Girl"

The second picture shows the referenced collection.

I currently have written the following piece (following this tutorial )

class Record {
  final String name;
  var color;
  final DocumentReference reference;
  Record.fromMap(Map<String, dynamic> map, {this.reference})
      : assert(map['name'] != null),
        assert(map['geslacht'] != null),
        name = map['name'],
        color = map['geslacht'];
  Record.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(snapshot.data, reference: snapshot.reference);  
  @override
  String toString() => "Record<$name:$votes>";
}

Which perfectly gets the data from the field called "name" and returns a instance of DocumentReference for the field called "geslacht"

I would love to get the information in this referenced document. So to conclude the value "pink" is what I am trying a get. (The path would be baby --> dana --> geslacht --> gender --> girl --> color --> pink )

Thanks in advance for the help!

Answer 1

You will have to get() the other document using that DocumentReference, just like you would if you built the DocumentReference yourself. Cloud Firestore will not automatically follow references for you - you have to write code for that.

Answer 2

You need to query for your data using that reference, you currently only grab that first document:

class Record {
  final String name;
  var color;
  final DocumentReference reference;
  Record.fromMap(Map<String, dynamic> map, {this.reference})
      : assert(map['name'] != null),
        assert(map['geslacht'] != null),
        name = map['name'],
        color = map['geslacht'];
  Record.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(snapshot.data, reference: snapshot.reference);  
  @override
  String toString() => "Record<$name:$votes>";
}

What you need to do is to perform another query like this:

_getGender(ref) async {
  // ref is '/gender/Girl/' in your case
  var query = await Firestore.instance.document(ref).get();
  print('color is: ' + query.data['color'])
}