Deleting document from cloud_firestore in flutter

Question

I am returning a streamBuilder and inside the streamBuider, it returns a widget.
Now I have wrap a widget with dismissible so that I can delete the document from the collection from the cloud_firestore.

showingTheSelectedDateEvents() {
    List<Widget> listViewContainer = [];

    return StreamBuilder<QuerySnapshot>(
      stream: firestoreInstance.collection('eventDetails').snapshots(),
      builder: (context, snapshot) {
        if (!snapshot.hasData) {
          return Center(
            child: CircularProgressIndicator(
              backgroundColor: Colors.lightBlueAccent,
            ),
          );
        }
        String theDatabaseDate;
        final allDocuments = snapshot.data.docs;
        //here we get all the documents from the snapshot.
        for (var i in allDocuments) {
          theDatabaseDate = i.data()['dateTime'];
          if (theDatabaseDate == theDataProvider.databaseSelectedDate) {
            print(theDatabaseDate +
                " is same as " +
                theDataProvider.databaseSelectedDate);
            listViewContainer.add(Dismissible(
              key: ObjectKey(snapshot.data.docs.elementAt(0)),
              onDismissed: (direction) {
                firestoreInstance
                    .collection("eventDetails")
                    .doc()
                    .delete()
                    .then((_) {
                  print("success!");
                });
              },
             child://here
          
            ));
            print(listViewContainer.length);
          } else {
            print("no any events for today");
          }
        }
        return Expanded(
          child: ListView(
            reverse: true,
            padding: EdgeInsets.symmetric(horizontal: 10.0, vertical: 20.0),
            children: listViewContainer,
          ),
        );
      },
    );
  }

I tried this for deleting the data from the cloud_firestore

key: ObjectKey(snapshot.data.docs.elementAt(0)),
onDismissed: (direction) {
                firestoreInstance
                    .collection("eventDetails")
                    .doc()
                    .delete()
                    .then((_) {
                  print("success!");
                });
              },           

I want to delete the specific document from the collection
I cannot figure out how to do that.
here is the database model

I am trying to delete the document of eventDetails collection.

Answer 1

doc() will generate a new random id, therefore if you don't have access to the id, then you need to do the following:

    FirebaseFirestore.instance
        .collection("eventDetails")
        .where("chapterNumber", isEqualTo : "121 ")
        .get().then((value){
          value.docs.forEach((element) {
           FirebaseFirestore.instance.collection("eventDetails").doc(element.id).delete().then((value){
             print("Success!");
           });
          });
        });

Use a where() condition to get the required document and delete it.

---

Since in your code you are using:

return StreamBuilder<QuerySnapshot>(
      stream: firestoreInstance.collection('eventDetails').snapshots(),

Here you are fetching all the documents under eventDetails, therefore you can add a unique field to the document and then inside the for loop you can get the id:

for (var i in allDocuments) {
          if(i.data()["subject"] == "Mathemtics")
               docId = i.id;

And then you can delete it:

              onDismissed: (direction) {
                FirebaseFirestore.instance
                    .collection("eventDetails")
                    .doc(docId)
                    .delete()
                    .then((_) {
                  print("success!");
                });
              },

This way you dont need to fetch the documents twice.

Answer 2

You can always query the document to get the document ID and perform the deletion.

var collection = FirebaseFirestore.instance.collection('users');
var snapshot = await collection.where('age', isGreaterThan: 20).get();
for (var doc in snapshot.docs) {
 await doc.reference.delete();
}

To delete all the documents, iterate through the QueryDocumentSnapshot.

var collection = FirebaseFirestore.instance.collection('collection');
var querySnapshots = await collection.get();
for (var doc in querySnapshots.docs) {
  await doc.reference.delete();
}