How to query mongodb wildcard sub fields in filter and projection?-CodePudding

I have this structure of a document:

{
  "1": {
    "type1": 1,
    "type2": 2
  },
  "2": {
    "type1": 11,
    "type2": 12
  }
}
// There can by multiple values at all levels, not just 2

Now I want to to query for all type2 with a filter, conceptually:

"*.type2" > 10

And I want to return only one field as well, so that the result would look like that:

{
  "10": {
    "type2": 20
  },
  "20": {
    "type2": 25
  }
}

Is it possible to achieve in MongoDB with a single query?

CodePudding user response：

One option is to iterate over the keys and keep only the type2 with value greater than 10. In order to iterate over the keys we are using $objectToArray. In order to keep only the type2, we use $reduce to iterate (which allow to format the item), instead of a simple $filter that will just return the un-formatted matching items. The last step is just to format back the array to a dictionary.

db.collection.aggregate([
  {$project: {
      _id: 0,
      data: {$reduce: {
          input: {$objectToArray: "$$ROOT"},
          initialValue: [],
          in: {$concatArrays: [
              "$$value",
              {$cond: [
                  {$gt: ["$$this.v.type2", 10]},
                  [{k: "$$this.k", v: {type2: "$$this.v.type2"}}],
                  []
              ]}
          ]}
      }}
  }},
  {$replaceRoot: {newRoot: {$arrayToObject: "$data"}}}
])

See how it works on the playground example