Can't convert _InternalLinkedHashMap<String, dynamic> to Map<String, dynamic>

Question

I'm trying to get data from cloud_firestore.

void _getData(){
    final getData = await FirebaseFirestore.instance
        .collection('users')
        .doc(id)
        .get();
    Map<String, dynamic> d = getData.data()!;

    for (dynamic i in d["tags"]) {
       .......
    }
}

But when _getData() is called, an error occurs at for (dynamic i in d["tags"]) .

 _TypeError (type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'Iterable<dynamic>')

I found this answer and changed my code.

Map<String, dynamic> d = getData.data()!;

to

Map<String, dynamic> d = Map<String, dynamic>.from(getData.data()!);

But the error never be fixed.

I don't want waste time with useless _InternalLinkedHashMap.

RunTimeType print

print("type: " + d["tags"].runtimeType.toString());

output

I/flutter (18762): type: _InternalLinkedHashMap<String, dynamic>

Answer 1

I found the error origin. when the specific document was broken, this error occurs.

In my case, I thought database was like this:

tags (array)
 |- tag1 (map)
     |- user (String)
     |- date (Timestamp)
 |- tag2 (map)
     |- user (String)
     |- date (Timestamp)
 ...

However the database was actually this:

tags (array)
 |- user (String)
 |- date (Timestamp)