db.command.aggregate.filter

1. Operator Description

Function: Returns a subset of the array that meets the given conditions.

Declaration: db.command.aggregate.filter({ input: array, as: string, cond: expression })

2. Operator Parameters

Field	Type	Required	Description
input	Expression	Required	An expression that resolves to an array.
as	string	No	Optional. The variable representing each element in the array, defaults to this.
cond	Expression	Required	An expression that resolves to a boolean value, used to determine whether each element meets the condition. The element name is defined by the as parameter (parameter names must be prefixed with $$, e.g., $$this).

3. Sample Code

Suppose the collection fruits contains the following records:

{
  "_id": 1,
  "stock": [
    { "name": "apple", "price": 10 },
    { "name": "orange", "price": 20 }
  ],
}
{
  "_id": 2,
  "stock": [
    { "name": "lemon", "price": 15 },
  ],
}

// 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('fruits')
    .aggregate()
    .project({
      stock: $.filter({
        input: '$stock',
        as: 'item',
        cond: $.gte(['$$item.price', 15])
      })
    })
    .end()
  console.log(res.data)
}

The returned result is as follows:

{ "_id": 1, "stock": [ { "name": "orange", "price": 20} ] }
{ "_id": 2, "stock": [ { "name": "lemon", "price": 15 } ] }