问在Cloud Function中运行Cloud Firestore事务

EN

exports.runMyTransaction = functions.firestore
    .doc('/myCollection/{myId}').onWrite((event) => {

    // In this transaction, I want to pass event instead of cityRef
    var transaction = db.runTransaction(t => {
    return t.get(cityRef)
        .then(doc => {
        // doc should contain the event object
        var newPopulation = doc.data().population + 1;
        t.update(cityRef, { population: newPopulation });
        });
    });

});