So I am creating an attendance app in which there is a list named attendees which contains the list of all students attending the lecture.
List<String> attendees = [uid0, uid1, uid2];
and the student data model is as follows
Student(
List<String> attendance = [at0, at1]; //this is the list of lectures attended
String name;
)
and the document name of every student is their user-id
How do I update the list of every student via the batch() function?
I assume you already have a list of attendees that contains user-id as you mentioned the userId would be the documentId in Firestore.
Therefore, you can do a loop and update your doc directly and then use commit to apply your changes.
updateBatch(List<String> attendees) async {
try {
final db = FirebaseFirestore.instance;
final WriteBatch batch = db.batch();
// based on this doc https://firebase.flutter.dev/docs/firestore/usage/#batch-write
// Each transaction or batch of writes can write to a maximum of 500 documents.
for (final userid in attendees) {
// Use the batch to update a document that exist otherwise it will throw error,
// in case you want to create that doc, maybe you should use `set` instead
// ref: https://pub.dev/documentation/cloud_firestore/latest/cloud_firestore/WriteBatch/update.html
batch.update(
//Give the ref of document.
db.document('Path/to/firestore/document'), // e.g: /Students/userId
//And the data to update.
{"key": value},
);
}
await batch.commit();
print('success');
} catch (e) {
print('error $e');
}
}
A few notes:
