db.command.aggregate.literal

1. Operator Description

Functionality: Directly returns the literal value of a given input without any parsing or processing.

Declaration: literal(<value>)

2. Operator Parameters

Field	Type	Required	Description
-	any	Required	If <value> is an expression, literal does not parse or evaluate it, but returns the expression directly.

3. Sample Code

For example, we have a collection items with the following data:

{ "_id": "0", "price": "$1" }
{ "_id": "1", "price": "$5.60" }
{ "_id": "2", "price": "$8.90" }

Using \$ in Literal Form

The following code uses literal to generate a new field isOneDollar, indicating whether the price field is strictly equal to "$1".

Note: We cannot use eq(['$price', '$1']) here because "$1" is an expression that represents the value of the "1" field, rather than the string literal "$1".

// 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
const _ = db.command

exports.main = async (event, context) => {
  const res = await db
    .collection('items')
    .aggregate()
    .project({
      isOneDollar: $.eq(['$price', $.literal('$1')])
    })
    .end()
  console.log(res.data)
}

The output is as follows:

{ "_id": "0", "isOneDollar": true }
{ "_id": "1", "isOneDollar": false }
{ "_id": "2", "isOneDollar": false }

Project a field to the value 1

The following code uses literal to project a new field amount with the value 1.

// 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
const _ = db.command

exports.main = async (event, context) => {
  const res = await db
    .collection('items')
    .aggregate()
    .project({
      price: 1,
      amount: $.literal(1)
    })
    .end()
  console.log(res.data)
}

The output is as follows:

{ "_id": "0", "price": "$1", "amount": 1 }
{ "_id": "1", "price": "$5.60", "amount": 1 }
{ "_id": "2", "price": "$8.90", "amount": 1 }