Consequences of using $ relind on nested arrays?

Question

Let's say I have 17,000 documents that have a structure similar to the document below:

{
   someInfo: "blah blah blah",
   // and another dozen or so attributes here, followed by:
   answers:[
      {
          email: "[e-mail],
          values:[
             {value: 1, label: "test1"},
             {value: 2, label: "test2"}    
          ]
      },
      {
          email: "[e-mail],
          values:[
             {value: 6, label: "test1"},
             {value: 1, label: "test2"}    
          ]
      }
   ]
}

Let's say I use an aggregate to unwind both answers, and answers.valuesas follows:

db.participants.aggregate(
   {$unwind: "$answers"},
   {$unwind: "$answers.values"}
);

I assume that it will create a fairly large set of results in memory, since it will essentially replicate the parent object 17,000 * # of answers * # of valuesonce.

, - , , , , . Mongo $unwind , , .

? db?

Answer 1

, $unwind ing - , .

$match, , , , , .

- $project. $project , , .

,

{
  someInfo: "blah blah blah",
  answers: [
    {
      email: "[e-mail]",
      values: [
        {value: 1, label: "test1"},
        {value: 2, label: "test2"}    
      ]
    },
    {
      email: "[e-mail]",
      values: [
        {value: 6, label: "test1"},
        {value: 1, label: "test2"}    
      ]
    }
  ]
}

db.collection.aggregate([{ $match: { <element>: <value> }}, { $project: { _id: 0, answers: 1}}])

someInfo , . $project ...

db.collection.aggregate([
   { $match: { <element>: <value> }},
   { $project: { _id: 0, answers: 1}},
   { $unwind: "$answers"},
   { $unwind: "$answers.tags"},
   { $project: { e: "$answers.email", v: "$answers.values"}}
])

, :

{ e: "[e-mail]", v: { value: 1, label: "test1" } }
{ e: "[e-mail]", v: { value: 2, label: "test2" } }
{ e: "[e-mail]", v: { value: 6, label: "test1" } }
{ e: "[e-mail]", v: { value: 1, label: "test2" } }

, , .