db.command.aggregate.mergeObjects

1. Operator Description

Function: Merges multiple documents into a single document.

Declaration: db.command.aggregate.max(<expression>)

There are two usage forms for expressions as follows:

• When used in group():

mergeObjects(<document>)

• When used in other expressions:

mergeObjects([<document1>, <document2>, ...])

2. Operator Parameters

Field	Type	Required	Description
-	Expression or <Array>Expression	Required	aggregate expression

3. Sample Code

Used with group()

Suppose the collection sales contains the following documents:

{ "_id": 1, "year": 2018, "name": "A", "volume": { "2018Q1": 500, "2018Q2": 500 } }
{ "_id": 2, "year": 2017, "name": "A", "volume": { "2017Q1": 400, "2017Q2": 300, "2017Q3": 0, "2017Q4": 0 } }
{ "_id": 3, "year": 2018, "name": "B", "volume": { "2018Q1": 100 } }
{ "_id": 4, "year": 2017, "name": "B", "volume": { "2017Q3": 100, "2017Q4": 250 } }

The following code uses mergeObjects() to merge documents with the same name:

// 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('sales')
    .aggregate()
    .group({
      _id: '$name',
      mergedVolume: $.mergeObjects('$volume')
    })
    .end()
  console.log(res.data)
}

The output is as follows:

{ "_id": "A", "mergedVolume": { "2017Q1": 400, "2017Q2": 300, "2017Q3": 0, "2017Q4": 0, "2018Q1": 500, "2018Q2": 500 } }
{ "_id": "B", "mergedVolume": { "2017Q3": 100, "2017Q4": 250, "2018Q1": 100 } }

General Usage

Suppose the collection test contains the following documents:

{ "_id": 1, "foo": { "a": 1 }, "bar": { "b": 2 } }
{ "_id": 2, "foo": { "c": 1 }, "bar": { "d": 2 } }
{ "_id": 3, "foo": { "e": 1 }, "bar": { "f": 2 } }

The following code uses mergeObjects() to merge the foo and bar fields in the documents into foobar:

// 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('sales')
    .aggregate()
    .project({
      foobar: $.mergeObjects(['$foo', '$bar'])
    })
    .end()
  console.log(res.data)
}

The output is as follows:

{ "_id": 1, "foobar": { "a": 1, "b": 2 } }
{ "_id": 2, "foobar": { "c": 1, "d": 2 } }
{ "_id": 3, "foobar": { "e": 1, "f": 2 } }