MongoDb. Get an object in a nested array

Question

I have a collection with documents like this one:

{
    "_id" : "bc923adf-ddd9-4987-a759-2d3f8dbffe3e",
    "title" : "DocumentTitle",        
    "nestedObjects" : [ 
        {
            "_id" : "3eef3a60-8d70-4640-b494-cb17e52e73a7",
            "startTime" : "21:00:00",
            "endTime" : "00:00:00"
        },
        {
            "_id" : "5aa8ca60-8d70-4640-b494-cb17e52e4caa",
            "startTime" : "17:00:00",
            "endTime" : "23:00:00"
        }
    ]
}

I need a query to get the 'nestedObject' that matches both Ids, root object Id and nested object Id. For instance, given root object Id equals "bc923adf-ddd9-4987-a759-2d3f8dbffe3e" and nested object Id equals "5aa8ca60-8d70-4640-b494-cb17e52e4caa", I want to get this result:

{
   "_id" : "5aa8ca60-8d70-4640-b494-cb17e52e4caa",
   "startTime" : "17:00:00",
   "endTime" : "23:00:00"
}

I tried with this query;

var nestedObject = db.myCollection.aggregate(
[
    { "$match" : { "_id" : "bc923adf-ddd9-4987-a759-2d3f8dbffe3e" } }, 
    { "$unwind" : "$nestedObjects" }, 
    { "$match" : { "nestedObjects._id" : "5aa8ca60-8d70-4640-b494-cb17e52e4caa" } }, 
    { "$project" : { "startTime" : "$nestedObjects.startTime", "endTime":"$nestedObjects.endTime" } }
]);

I expected to be able to access starTime and endTime properties using nestedObject.startTime with no luck. Also, I'd like to get the whole nested object without the need of listing all its properties in the project phase.

What am I doing wrong? Is there an easier query I could run?

Thanks.

Answer 1

Replace your $project stage with a $replaceRoot:

{ "$replaceRoot" : { newRoot: "$nestedObjects" } }