如何使用Firebase云功能查询数据库

Question

I am trying to query my firestore database using cloud functions. I want to trigger an email notification every time a new reading in my database is under the value of 10.

Here is the relevant database structure for reference: database structure . The "readings" field is an array and each "reading" is a map which holds the fields "date" and "value".

Currently I am at the point where I can send an email notification every time a new user is created however I want this to work for the database. I am unsure how to query for the "readings" array and then for each individual reading.

Here is my code so far which sends an email when a new user is created

 exports.sendNotification = functions.auth.user().onCreate((user) => { const mailOptions = { from: '"Spammy Corp." <noreply@firebase.com>', to:"fakeEmail@btopenworld.com", text: "TEST" }; return mailTransport.sendMail(mailOptions) .then(() => console.log("It worked")) .catch((error) => console.error('There was an error while sending the email:', error)); }); 

Answer 1

See: https://firebase.google.com/docs/firestore/extend-with-functions

For example, to fire on all new readings added to that first child:

exports.sendEmail = functions.firestore
    .document('sensor/UGt.../readings')
    .onCreate((snap, context) => {
        const newValue = snap.data();
        const value = newValue.value;
        if (value < 10) {
            // send email
        }
    });

In further comments you mentioned listening for new readings in all sensor elements, not just your first one. This is unfortunately not possible in an efficient / simple way ( source ). Instead you will have to listen to all onUpdate events on /sensor/ , check if the update is adding a reading, then check the value & send your email.

It may be easier to call the cloud function directly from wherever adds the reading, depending on how many times the /sensor/ path is going to be updated for other reasons (since every time this happens, it's a waste of resources).