How to handle division by zero in MongoDB aggregation framework

Question

I have a collection of items that can be upvoted or downvoted.

{\"_id\" : 1, \"name\": \"foo\", \"upvotes\" : 30, \"downvotes\" : 10}
{\"_id\" : 2, \"name\": \"b         


        

Answer 1

You might want to use the $cond operator to handle this:

db.items.aggregate([
    {"$project":
        {
            "name": "$name",
            "upvotes": "$upvotes",
            "downvotes": "$downvotes",
            "quality": { $cond: [ { $eq: [ "$downvotes", 0 ] }, "N/A", {"$divide":["$upvotes", "$downvotes"]} ] }
        }
    },
    {"$sort": {"quality":-1}}
]);

Answer 2

You want the $cond operator. http://docs.mongodb.org/manual/reference/operator/aggregation/cond/

Something like:

{"$project":
  {
    "name": "$name",
    "upvotes": "$upvotes",
    "downvotes": { $cond: [ { $eq: ["$downvotes", 0] }, 1, "$downvotes"] } 
  }
},