Get specific values nested arrays elements in mongo collection by date - mongodb

Question

I have a collection with objects like this:
{
"_id": ObjectId("52ed12c144aecc4bf004d0b6"),
"title": "myBook",
"summary": "This is a book summary",
"chapters": [
{
"number": 1
"created_at": ISODate("2013-12-17T23:00:00Z")
},
{
"number": 2
"created_at": ISODate("2014-12-17T23:00:00Z")
}
]
"covers": [
"http://url.com/cover1.jpg",
"http://url.com/cover2.jpg",
],
"urls": [
"http://url.com/myBook",
"http://url.com/myBook/option2"
],
"genres": [
"comedy",
"romantic"
],
"created_at": ISODate("2012-12-17T23:00:00Z"),
"modify_at": ISODate("2014-02-01T15:41:48.149Z")
}
I only want to get books which 'crated_at' >= '2012-12-17T23:00:00Z' with only the chapters which 'created_at' > "2013-12-17T23:00:00Z". (As a filter)
My output json should be something like this:
{
"_id": ObjectId("52ed12c144aecc4bf004d0b6"),
"title": "myBook",
"summary": "This is a book summary",
"chapters": [
{
"number": 2
"created_at": ISODate("2014-12-17T23:00:00Z")
}
]
"covers": [
"http://url.com/cover1.jpg",
"http://url.com/cover2.jpg",
],
"urls": [
"http://url.com/myBook",
"http://url.com/myBook/option2"
],
"genres": [
"comedy",
"romantic"
],
"created_at": ISODate("2012-12-17T23:00:00Z"),
"modify_at": ISODate("2014-02-01T15:41:48.149Z")
}
In the query output could be books without any chapters, others with a subset of all their chapters or books with all their chapters.
For to search books by 'created_at' I query by:
db.books.find({ created_at: {$gte: ISODate("2012-12-17T23:00:00Z")} })
but I don't know what I have to add for to filter the chapters in the output of this result.

Answer 1

You could try to do it with aggregation framework.
db.chapters.aggregate(
{ $match: { created_at: {$gte: ISODate("2012-12-17T23:00:00Z")} } },
{ $unwind: "$chapters" },
{ $match: { "chapters.created_at": {$gte: ISODate("2013-12-17T23:00:00Z")} } },
{ $group:
{
_id:
{
id: "$_id",
title: "$title",
summary: "$summary",
covers: "$covers",
urls: "$urls",
genres: "$genres",
created_at: "$created_at",
modify_at: "$modify_at"
},
chapters: { $push: "$chapters" }
}
},
{ $project:
{
_id: "$_id.id",
title: "$_id.title",
summary: "$_id.summary",
chapters: "$chapters",
covers: "$_id.covers",
urls: "$_id.urls",
genres: "$_id.genres",
created_at: "$_id.created_at",
modify_at: "$_id.modify_at"
}
}
)