How can I get specific document data from firestore querysnapshot?

Question

I got a querysnapshot in a function. And want to bring the whole querysnapshot to another function (functionTwo). In functionTwo, I want to get a specific document in the querysnapshot WITHOUT forEach. The specific doc can be changed by different cases.

ref_serial_setting.get()
    .then(querysnapshot => {
      return functionTwo(querysnapshot)
    })
    .catch(err => {
      console.log('Error getting documents', err)
    })


let functionTwo = (querysnapshot) => {
  // getting value

  const dataKey_1 = "dataKey_1"

  // Tried 1
  const value = querysnapshot.doc(dataKey_1).data()

  // Tried 2
  const value = querysnapshot.document(dataKey_1).data()

  // Tried 3 (Put 'data_name': dataKey_1 in that doc)
  const value = querysnapshot.where('data_name', '==', dataKey_1).data()
}

The result are all these trying are not a function.

How can I get specific document data from querysnapshot??

or

Is there any easy method to change the querysnapshot to JSON?

Answer 1

You can get an array of the document snapshots by using the docs property of a QuerySnapshot. After that you'll have to loop through getting the data of the doc snapshots looking for your doc.

const docSnapshots = querysnapshot.docs;

for (var i in docSnapshots) {
    const doc = docSnapshots[i].data();

    // Check for your document data here and break when you find it
}

Or if you don't actually need the full QuerySnapshot, you can apply the filter using the where function before calling get on the query object:

const dataKey_1 = "dataKey_1";    
const initialQuery = ref_serial_setting;
const filteredQuery = initialQuery.where('data_name', '==', dataKey_1);

filteredQuery.get()
    .then(querySnapshot => {
        // If your data is unique in that document collection, you should
        // get a query snapshot containing only 1 document snapshot here
    })

    .catch(error => {
        // Catch errors
    });

Answer 2

Theres an easy way to do this, each QuerySnapshot has a property docs which returns an array of QueryDocumentSnapshots. See QuerySnapshot documentation.

let citiesRef = db.collection('cities');
let query = citiesRef.where('capital', '==', true).get().then(snapshot => {
  snapshot.docs[0]; // => returns first document
});