db.command.aggregate.indexOfCP

1. Operator Description

Description: Searches for a substring in a target string and returns the code point index (starting from 0) of the first occurrence in UTF-8. If the substring does not exist, returns -1.

Declaration: db.command.aggregate.indexOfCP([<target string expression>, <substring expression>, <start position expression>, <end position expression>])

Notes:

A code point is a "code position", also known as an "encoding position". Here it specifically refers to the code points in the Unicode standard, ranging from 0 (hexadecimal) to 10FFFF (hexadecimal).

2. Operator Parameters

Field	Type	Required	Description
-	<Array>Expression	Required	Array of aggregate expressions, with the meaning of each element as follows

Below are the detailed descriptions of the 4 expressions:

Expression	Description
Target String Expression	Any expression that can be resolved to a string
Substring Expression	Any expression that can be resolved to a string
Start Position Expression	Any expression that can be resolved to a non-negative integer
End Position Expression	Any expression that can be resolved to a non-negative integer

3. Sample Code

Suppose the collection students contains the following records:

{ "firstName": "Yuanxin", "group": "a", "lastName": "Dong", "score": 84 }
{ "firstName": "Weijia", "group": "a", "lastName": "Wang", "score": 96 }
{ "firstName": "Chengxi", "group": "b", "lastName": "Li", "score": 80 }

Using indexOfCP to find the position of the character "a" in the field firstName:

// 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('students')
    .aggregate()
    .project({
      _id: 0,
      aStrIndex: $.indexOfCP(['$firstName', 'a'])
    })
    .end()
  console.log(res.data)
}

The returned result is as follows:

{ "aStrIndex": 2 }
{ "aStrIndex": 5 }
{ "aStrIndex": -1 }