MongoDB aggregation query - return all items inside nested subdocument

Basically, I have a nested array of objects. I want to extract information from those objects, and return all the results as an array.

Here is my data:

[    {      "_id": "608642db80a36336946620aa",      "title": "titleHere",      "types": {        "flashcardReversed": [          {            "normal": { // the data inside of "normal" should become its own object in the returned array              "_id": "608d5b290e635ece6828141X",              "front": "2front",              "back": "2back"            },            "reversed": { // the data inside of "reversed" should become its own object in the returned array              "_id": "608t5b290e635ece6828141Y",              "front": "2frontReversed",              "back": "2backReversed"            }          },          {            "normal": {              "_id": "608a5b31a3f9806de253726X",              "front": "2front2",              "back": "2back2"            },            "reversed": {              "_id": "608a5b31a3f9806de253726Y",              "front": "2frontReversed2",              "back": "2backReversed2"            }          }        ]      }    }  ]  

Here is the desired result:

[    {      "flashcardReversed": [        {          "_id": "608d5b290e635ece6828141X",          "front": "2front",          "back": "2back"        },        {          "_id": "608t5b290e635ece6828141Y",          "front": "2frontReversed",          "back": "2backReversed"        },        {          "_id": "608t5b290e635ece6828141Y",          "front": "2frontReversed",          "back": "2backReversed"        },        {          "_id": "608a5b31a3f9806de253726Y",          "front": "2frontReversed2",          "back": "2backReversed2"        }      ]    }  ]  

My current attempt: https://mongoplayground.net/p/k3Fjd59KMKg I have tried merging the $card and $card2 documents through various methods, and then using $replaceRoot to create the desired result - but after much time trying, I was unsuccessful.

Some notes about my use-case - I will be using this pipeline inside $facet There will be many objects inside of flashcardReversed, all created from the same Mongoose Schema

The document should have a max of ~2000 cards. I need the results for use in a react website. Should I be worried about the efficiency of this search? (if this should be a question in itself I would be happy to move it).

If my Mongoose Schemas would be helpful, let me know and I can add them.

All help is appreciated,

- Riley Swinson

https://stackoverflow.com/questions/67394118/mongodb-aggregation-query-return-all-items-inside-nested-subdocument May 05, 2021 at 09:36AM