如何将元素数组转换为 MongoDB 投影中的对象

Question

I tried to use $project and $arrayToObject but I can't figure how it works. My MongoDB query returns an array of objects:

[{ amounts: [ 10, 20, 30 ], id: "0x3c93" }, { amounts: [ 0, 0, 100 ], id: "0xee10" }]

And I want to group the results by "id" as key and "amounts" as value:

{"0x3c93": [ 10, 20, 30 ], "0xee10": [ 0, 0, 100 ]}

What is the correct expression to achieve this projection? I am using the node.js driver.

Answer 1

One option is to $group them to an array and format them to k , v before using $arrayToObject :

db.collection.aggregate([
  {$group: {_id: 0, data: {$push: {k: "$id", v: "$amounts"}}}},
  {$project: {_id: 0, data: {$arrayToObject: "$data"}}},
  {$replaceRoot: {newRoot: "$data"}}
])

See how it works on the playground example