Nrthugu

I realise this question is marked as a duplicate - but I think this question is more comprehensive and easier to understand, and therefore more likely to help others. (^__^)

I have read about reading data from Firebase realtime database.
https://firebase.google.com/docs/database/admin/retrieve-data

What I have not found is any documentation on how to control what data gets returned from the read query.

Consider the following structure:

-users

  -EiYu7OWooToo6noo

    alias: "Kermit"

    createdAt: 1538330532000

    firstName: "Kermit"

    surName: "Frogman" 

    pictureURL: "/imgs/kermit.png"

    phonePrimary: "555-1234"

    email: "kermit@themuppetshow.com"

    -myBooks

      -A1234567890

        title: "Frogs 101"

      ...

Is there a way to tell Firebase realtime database to only return some of the document data?

This code returns the entire document:

var ref = db.ref(`users/${uid}`);



ref.once("value", (snapshot) => {

  console.log(snapshot.val());

}, function (errorObject) {

  console.log("The read failed: " + errorObject.code);

});

Would it be possible to only get a partial document, for example:

    {

      alias: "Kermit"

      firstName: "Kermit"

    }

My reasoning is that this would be a huge performance gain when reading large amount of data. But is it possible?

You can't select a subset of child nodes for a query. Every query at a node always fetches the entire contents of the node - all the children and their children.

If you want only a subset of children, you have to perform different queries for each one. Alternatively, you can organize your data in such a way that commonly grouped fields are collected together at a particular node.