Search on multiple collections in MongoDB

Question

I know the theory of MongoDB and the fact that is doesn\'t support joins, and that I should use embeded documents or denormalize as much as possible, but here goes:

Answer 1

So now join is possible in mongodb and you can achieve this using $lookup and $facet aggregation here and which is probably the best way to find in multiple collections

db.collection.aggregate([
  { "$limit": 1 },
  { "$facet": {
    "c1": [
      { "$lookup": {
        "from": Users.collection.name,
        "pipeline": [
          { "$match": { "first_name": "your_search_data" } }
        ],
        "as": "collection1"
      }}
    ],
    "c2": [
      { "$lookup": {
        "from": State.collection.name,
        "pipeline": [
          { "$match": { "name": "your_search_data" } }
        ],
        "as": "collection2"
      }}
    ],
    "c3": [
      { "$lookup": {
        "from": State.collection.name,
        "pipeline": [
          { "$match": { "name": "your_search_data" } }
        ],
        "as": "collection3"
      }}
    ]
  }},
  { "$project": {
    "data": {
      "$concatArrays": [ "$c1", "$c2", "$c3" ]
    }
  }},
  { "$unwind": "$data" },
  { "$replaceRoot": { "newRoot": "$data" } }
])