Calculating the size of an array of objects using Mongoose's aggregate function

Question

Calculating the size of an array of objects using Mongoose's aggregate function

I have a specific document in my collection that I need help with:

{
"_id" : ObjectId("5b8aaaebf57de10e080c9151"),
"user_email" : "<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="b9cddcd4c9f9cddcd4c997dad6d4">[email protected]</a>",
"platforms_budget" : [ 
    {
        "_id" : ObjectId("5b8aaaebf57de10e080c9154"),
        "platform_id" : "f_01",
        "platform_name" : "Facebook"
    }, 
    {
        "_id" : ObjectId("5b8aaaebf57de10e080c9153"),
        "platform_id" : "i_01",
        "platform_name" : "Instagram"
    }, 
    {
        "_id" : ObjectId("5b8aaaebf57de10e080c9152"),
        "platform_id" : "f_02",
        "platform_name" : "Facebook_Adds"

    }
],
"__v" : 0

}

My task is to locate a specific user using their email address under "user_email" and determine the length of the associated "platform_budget" array. In this instance, the expected array length is 3.

The function I am utilizing for this task is shown below:

var BudgetSchema = require('../models/Budget');

router.post('/temp', async function (req, res) {
var length = await BudgetSchema.aggregate(
[{ $match: { user_email: "<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="bacedfc9cefacedfc9ce94d9d5d7">[email protected]</a>" } }, { $unwind: "$platforms_budget" },
{ $project: { "platforms_budget.count": { $size: '$platforms_budget' } } }])

console.log(length);
})

Upon attempting to log the value of length, an empty array is returned.

I have reviewed similar solutions on websites like this one, but I am still unable to grasp what mistake I am making or how to access the size information from the response. Can anyone assist me in determining the size of the "platforms_budget" array?

Your guidance is greatly appreciated.

javascript mongodb mongoose size aggregate

Answer 1

Answer №1

When ../models/Budget exports a Model, the Model#aggregate(Array, Function) function requires the pipeline with aggregations in an array format, along with an optional callback function that handles any errors and results.

.aggregate([...], function(error, result) {
    // handle actions here
});

Alternatively, you can also utilize the Aggregate object directly and use .exec(Function) method with a callback function.

.aggregate([...]).exec(function(error, result) {
    // handle actions here
});

I still find the documentation regarding .aggregate(Array, Function) a bit confusing.

If a callback is provided, the aggregate operation is executed and a Promise is returned. If no callback is provided, the aggregate itself is returned.

The statement seems to suggest that a promise is returned when a callback is used, but I could not locate any evidence of a promise being returned by .aggregate(Array, Function) on GitHub.

Answer 2

When ../models/Budget exports a Model, the Model#aggregate(Array, Function) function requires the pipeline with aggregations in an array format, along with an optional callback function that handles any errors and results.

.aggregate([...], function(error, result) {
    // handle actions here
});

Alternatively, you can also utilize the Aggregate object directly and use .exec(Function) method with a callback function.

.aggregate([...]).exec(function(error, result) {
    // handle actions here
});

I still find the documentation regarding .aggregate(Array, Function) a bit confusing.

If a callback is provided, the aggregate operation is executed and a Promise is returned. If no callback is provided, the aggregate itself is returned.

The statement seems to suggest that a promise is returned when a callback is used, but I could not locate any evidence of a promise being returned by .aggregate(Array, Function) on GitHub.

Calculating the size of an array of objects using Mongoose's aggregate function

Answer №1

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