Mongo Query - $group-CodePudding

Is it possible with Mongo to make this transformation (with a $group I think) ? or should it be done with JavaScript on the client side ?

[
  {
    id: 1,
    lib: 'x'
  },
  {
    id: 2,
    lib: 'a'
  },
  {
    id: 1,
    lib: 'b'
  },
  {
    id: 1,
    lib: 'v'
  }
]

[
  {
    id: 1,
    lib_1: 'x',
    lib_2: 'b',
    lib_3: 'v'
  },
  {
    id: 2,
    lib_1: 'a'
  }
]

CodePudding user response：

Query

with $group you can easily put them in an array, and i think its best to just do this
but if you want the exact output like in your expected output its more complicated, because you need to convert array to object, and add numbers in keys etc, in general in mongodb fields are not made for data, because queries become harder, fields are for the schema

Playmongo

aggregate(
[{"$group": {"_id": "$id", "libs": {"$push": "$lib"}}},
 {"$set": 
   {"libs": 
     {"$map": 
       {"input": {"$range": [0, {"$size": "$libs"}]},
        "in": 
         {"k": {"$concat": ["lib_", {"$toString": {"$add": ["$$this", 1]}}]},
          "v": {"$arrayElemAt": ["$libs", "$$this"]}}}}}},
 {"$set": {"libs": {"$arrayToObject": ["$libs"]}}},
 {"$replaceRoot": {"newRoot": {"$mergeObjects": ["$libs", "$$ROOT"]}}},
 {"$project": {"libs": 0}}])