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Is it acceptable to increment a counter with a realtime database trigger using transaction?
exports.incPostCount = functions.database.ref('/threadsMeta/{threadId}/posts') .onWrite(event => { admin.database().ref('/analytics/postCount') .transaction(count => { if (count === null) { return count = 1 } else { return count + 1 } }) }); 
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Firestore now has a specific operator for this called FieldValue. increment() . By applying this operator to a field, the value of that field can be incremented (or decremented) as a single operation on the server.
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A FieldValue is a union type that may contain a primitive (like a boolean or a double), a container (e.g. an array), some simple structures (such as a Timestamp ) or some Firestore-specific sentinel values (e.g. ServerTimestamp ) and is used to write data to and read data from a Firestore database.
Definitely! In fact, that's exactly how it's done in this code sample, although with a few small differences:
exports.countlikechange = functions.database.ref("/posts/{postid}/likes/{likeid}").onWrite((event) => { var collectionRef = event.data.ref.parent; var countRef = collectionRef.parent.child('likes_count'); return countRef.transaction(function(current) { if (event.data.exists() && !event.data.previous.exists()) { return (current || 0) + 1; } else if (!event.data.exists() && event.data.previous.exists()) { return (current || 0) - 1; } }); }); Notably, this sample handles both an increment and a decrement case depending on whether the child node is being created or deleted.
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