Flattening mongoDB schema

Question

I have an existing deeply nested mongoDB schema that I must flatten as I have a complex query that cannot be efficiently made with the current structure. Here is the MWE of the

Answer 1

The following

db.collection.aggregate(
    [{$unwind:"$tests"},
    {$unwind:"$tests.details"},
    {$unwind:"$tests.details.a"},
    {$group:{
        _id:"$_id",
        "tests": {"$push":{
            "aPos":"$tests.details.a.pos",
            "aSize":"$tests.details.a.size",
            "aUnit":"$tests.details.a.unit"
        }}}},
    ])

produces:

{ "_id" : ObjectId("58e574a768afb6085ec3a388"), "tests" : [ { "aPos" : "Far", "aSize" : "5", "aUnit" : "08" } ] }

The above only yielded one set of field:value pairs; doing multiple $unwind at the same level did not work:

db.collection.aggregate(
    [{$unwind:"$tests"},
    {$unwind:"$tests.details"},
    {$unwind:"$tests.details.a"},
    {$unwind:"$tests.details.b"},
    {$group:{
        _id:"$_id",
        "tests": {"$push":{
            "aPos":"$tests.details.a.pos",
            "aSize":"$tests.details.a.size",
            "aUnit":"$tests.details.a.unit",
            "bPos":"$tests.details.b.pos",
            "bSize":"$tests.details.b.size",
            "bUnit":"$tests.details.b.unit"
        }}}},
    ])  //does not run

Therefore, there needs to be another aggregation stage of $facet to carry out similar steps for details.b, details.c and details.d.