db.command.aggregate.dayOfMonth

1. Operator Description

Function: Returns the day of the month for a date field, which is a number between 1 and 31.

Declaration: db.command.aggregate.dayOfMonth(<date field>)

2. Operator Parameters

Field	Type	Required	Description
-	Expression	Required	Date field

3. Sample Code

Suppose the collection dates contains the following documents:

{
  "_id": 1,
  "date": ISODate("2019-05-14T09:38:51.686Z")
}

We use dayOfMonth() to project the date field and obtain the corresponding day of the month:

// Sample code in the Cloud Function environment
const tcb = require('@cloudbase/node-sdk')
const app = tcb.init({
  env: 'xxx'
})

const db = app.database()
const $ = db.command.aggregate

exports.main = async (event, context) => {
  const res = await db
    .collection('dates')
    .aggregate()
    .project({
      _id: 0,
      dayOfMonth: $.dayOfMonth('$date')
    })
    .end()
  console.log(res.data)
}

The output is as follows:

{
  "dayOfMonth": 14
}