Aggregate.group

1. Interface Description

Function: Groups input records by a given expression, with each output record representing a group and each record's _id serving as the key distinguishing different groups. Output records can also include accumulated values, where setting an output field to an accumulated value calculates it from the group.

Syntax: group({ _id: <expression>, <field1>: <accumulator1>, ... <fieldN>: <accumulatorN> })

2. Input Parameters

Parameter	Type	Required	Description
_id	expression	Yes	is the key used to distinguish different groups
fieldN	expression	No	fieldN: These additional fields are optional and represent accumulated values. Use accumulators like $.sum, but other expressions can also be employed.

The accumulator must be one of the following operators:

• addToSet
• avg
• first
• last
• max
• min
• push
• stdDevPop
• stdDevSamp
• sum

Memory Limit

This stage has a 100M memory usage limit.

3. Response

Parameter	Type	Required	Description
-	Aggregate	Yes	Aggregation object

4. Sample Code

Grouping by Field Value

Suppose the collection avatar contains the following records:

{
  _id: "1",
  alias: "john",
  region: "asia",
  scores: [40, 20, 80],
  coins: 100
}
{
  _id: "2",
  alias: "arthur",
  region: "europe",
  scores: [60, 90],
  coins: 20
}
{
  _id: "3",
  alias: "george",
  region: "europe",
  scores: [50, 70, 90],
  coins: 50
}
{
  _id: "4",
  alias: "john",
  region: "asia",
  scores: [30, 60, 100, 90],
  coins: 40
}
{
  _id: "5",
  alias: "george",
  region: "europe",
  scores: [20],
  coins: 60
}
{
  _id: "6",
  alias: "john",
  region: "asia",
  scores: [40, 80, 70],
  coins: 120
}

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("avatar")
    .aggregate()
    .group({
      _id: "$alias",
      num: $.sum(1),
    })
    .end();
  console.log(res.data);
};

The returned result is as follows:

{
  "_id": "john",
  "num": 3
}
{
  "_id": "authur",
  "num": 1
}
{
  "_id": "george",
  "num": 2
}

Grouping by Multiple Values

You can group by multiple values by passing a record to _id. Still using the example data from above, group by region with the same highest score, and calculate the total coins amount for each group.

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("avatar")
    .aggregate()
    .group({
      _id: {
        region: "$region",
        maxScore: $.max("$scores"),
      },
      totalCoins: $.sum("$coins"),
    })
    .end();
  console.log(res.data);
};

The returned result is as follows:

{
  "_id": {
    "region": "asia",
    "maxScore": 80
  },
  "totalCoins": 220
}
{
  "_id": {
    "region": "asia",
    "maxScore": 100
  },
  "totalCoins": 100
}
{
  "_id": {
    "region": "europe",
    "maxScore": 90
  },
  "totalCoins": 70
}
{
  "_id": {
    "region": "europe",
    "maxScore": 20
  },
  "totalCoins": 60
}