$multiply query not working in Document DB

Question

We have created a documentDb instance having a 4.0.0 version. When running the query using $muliply it throws an error as Bad Query.

Query: 'test': { $multiply: "$price", 8 }

When checking the documentation it says the $muliply is supported. Not sure why it throws a Bad Query

Answer 1

There should be square braces encasing the field and the multiplier.

'test': { $multiply: ["$price", 8 ]}

If you still get an error, it might be that you are You have to make sure that price is not stored as string. You can use $toInt to change it to an integer or $toDouble if you are expecting decimals.

'test': { $multiply: [{$toInt:"$price"}, 8 ]}

Answer 2

Something is wrong in your code, $multiply works as expected in Amazon DocumentDB:

rs0:PRIMARY> db.collection.find().pretty()
{
    "_id" : ObjectId("62693003512474f1017b6ce2"),
    "name" : "prod1",
    "price" : 10
}
{
    "_id" : ObjectId("62693009512474f1017b6ce3"),
    "name" : "prod2",
    "price" : 20
}
rs0:PRIMARY>
rs0:PRIMARY> db.collection.aggregate(
...    [
...      { $project: { _id:0, total: { $multiply: [ "$price", 8 ] } } }
...    ]
... )
{ "total" : 80 }
{ "total" : 160 }