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exports.aggregateRatings = functions.firestore |
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.document('restaurants/{restId}/ratings/{ratingId}') |
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.onWrite((change, context) => { |
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// Get value of the newly added rating |
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var ratingVal = change.after.data().rating; |
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|
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// Get a reference to the restaurant |
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var restRef = db.collection('restaurants').doc(context.params.restId); |
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|
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// Update aggregations in a transaction |
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return db.runTransaction(transaction => { |
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return transaction.get(restRef).then(restDoc => { |
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// Compute new number of ratings |
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var newNumRatings = restDoc.data().numRatings + 1; |
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|
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// Compute new average rating |
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var oldRatingTotal = restDoc.data().avgRating * restDoc.data().numRatings; |
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var newAvgRating = (oldRatingTotal + ratingVal) / newNumRatings; |
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// Update restaurant info |
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return transaction.update(restRef, { |
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avgRating: newAvgRating, |
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numRatings: newNumRatings |
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}); |
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}); |
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}); |
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}); |
If it's retried, I think it's possible to get a wrong value for newNumRatings.
