What's best practice "joining" a bunch of values in mongoose/mongodb without populate

Question

Let me start off by stating that I'm aware of the populate method that mongoose offers, but since my work has decided to move to native mongodb drivers in the future, I can no longer rely on populate to avoid work for myself latter on.

If I have two collections of Documents

People
{_id:1, name:Austin}
{_id:2, name:Doug}
{_id:3, name:Nick}
{_id:4, name:Austin}

Hobbies:
{Person: 1,  Hobby: Cars}
{Person:1, Hobby: Boats}
{Person:3, Hobby: Chess}
{Person:4, Hobby: Cars}

How should I go about joining each document in people with Hobbies. Ideally I would prefer to only have to call the database twice once to get the people and the second time to get the hobbies, and then return to the client app objects with them joined toeghter.

Answer 1

It depends on what is your primary concern. Generally, I would say to embed the hobbies into the People, like:

{
  "_id":1,
  "name":"Austin",
  "hobbies": [
    "Cars","Boats"
  ]
},
{
  "_id":2,
  "name":"Doug",
  "hobbies": []
},

{
  "_id":3,
  "name":"Nick",
  "hobbies": [
    "Chess"
  ]
},

{
  "_id":4,
  "name":"Austin",
  "hobbies": [
    "Cars"
  ]
}

which would give you the possibility of using a multi keyed index on hobbies and allow queries like this:

db.daCollection.find({"hobbies":"Cars"})

which would return both Austins as complete documents. Yes, I know that there would be a lot of redundant entries. If you would try to prevent that, could model it like this:

{
  "_id": 1,
  "name":"Cars"
},...

{
  "_id":1,
  "name":"Austin",
  "hobbies": [
    1, ...
  ]
}

which would need an additional index on the name field of the hobby to be efficient. So when you would want to find every person which is into cars, you would need to find the _id and query for it like

db.person.find({"hobbies":1})

I think it is easier, more intuitive and for most use cases faster if you use the embedding.