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db.command.aggregate.cmp

1. Operator Description​

Function: Given two values, returns their comparison result.

Declaration: db.command.aggregate.cmp([expression1, expression2])

  • If the first value is less than the second value, return -1
  • If the first value is greater than the second value, return 1
  • If the two values are equal, return 0

2. Operator Parameters​

FieldTypeRequiredDescription
-<Array>ExpressionRequiredAn array containing two aggregation expressions

3. Sample Code​

Suppose the collection price contains the following records:

{ "_id": 1, "shop1": 10, "shop2": 100 }
{ "_id": 2, "shop1": 80, "shop2": 20 }
{ "_id": 3, "shop1": 50, "shop2": 50 }

Compare the prices of all items between shop1 and shop2.

// 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('price').aggregate()
    .project({
      compare: $.cmp(['$shop1', '$shop2']))
    })
    .end()
  console.log(res.data)
}

The returned result is as follows:

{ "_id": 1, "compare": -1 }
{ "_id": 2, "compare": 1 }
{ "_id": 3, "compare": 0 }