Emulating a map() across multiple collections

marr · April 14, 2022, 8:25pm

I have some data stored in separate collections, and I’d like to essentially merge ($unionWith) them and return a normalized shape. In JS, it would look something like:

const types = ['type 1', 'type 2'];
[coll1, coll2].flatMap((coll, i) => coll.map(data => ({ type: types[i], data }))

The resulting data looking something like:
[{ type: 'type 1', data }, { type: 'type 1', data }, { type: 'type 2', data }]

My approach using mongo aggregations looks like this:

gist.github.com

https://gist.github.com/marr/a466f16482be02e098225e2d5e416eea

map.js

use example;
db.dropDatabase();

db.coll1.insertMany([{
    created_at: new Date(),
    text: 'abc'
}, {
    created_at: new Date(),
    text: 'bbb'
}]);

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Would you be able to help me optimize/simplify/reorganize that, if possible? I just want to make sure I’m not missing an easier way.

Thanks!