mongoose sum a value across all documents

Question

I am looking to count all columns with the name amount in the documents that match my query,

 tickets.count({time: {$gte: a}, time: {$lte: tomorrow}}).then(function (numTickets) {

How can I get the total result of the document column called amount?

Example, if I do have:

{ time: 20, amount: 40}
{ time: 40, amount: 20}

it would return the total amount(60)?

Remember that I do need to use {time: {$gte: a}, time: {$lte: tomorrow} in the query.

How would I do this?

Answer 1

Try it with the aggregation framework using the $match and $group operators, i.e. something like this

db.tickets.aggregate([
    { $match: { time: {$gte: a, $lte: tomorrow} } },
    { $group: { _id: null, amount: { $sum: "$amount" } } }
])

for example with test data like this

/* 1 */
{
    "_id" : ObjectId("57e0ed40828913a99c2ceb46"),
    "time" : 20,
    "amount" : 40
}

/* 2 */
{
    "_id" : ObjectId("57e0ed40828913a99c2ceb47"),
    "time" : 40,
    "amount" : 20
}

/* 3 */
{
    "_id" : ObjectId("57e0ed40828913a99c2ceb48"),
    "time" : 50,
    "amount" : 10
}

/* 4 */
{
    "_id" : ObjectId("57e0ed40828913a99c2ceb49"),
    "time" : 10,
    "amount" : 5
}

a pipeline (with dummy time range) like the following

db.tickets.aggregate([
    { $match: { time: {$gte: 20, $lte: 40} } },
    { $group: { _id: null, amount: { $sum: "$amount" } } }
])

would give you a result like this

/* 1 */
{
    "_id" : null,
    "amount" : 60
}

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