MongoDb Access array of objects with certain property - mongodb

Question

I have one document as follows:
{
user: 'hvt07',
photos: [
{
link: 'http://link.to.com/image1.jpg',
isPrivate: true
},
{
link: 'http://link.to.com/image2.jpg',
isPrivate: false
}
]
}
I want to get all photos which are with:
isPrivate: false
I am using the following query:
db.collection_name.find({ photos:{ $elemMatch:{isPrivate: false} } }).pretty()
I have also tried:
db.collection_name.find({'photos.isPrivate': true}).pretty()
But both return all elements in the array even ones that are set as :
isPrivate: true
Please suggest.

Answer 1

Aggregation is the solution.
You need to deconstruct the photos array using the $unwind operator. Next use the $match to select documents where isPrivate: false. The $group you can regroup your documents by _id and reconstruct your photos array using the $push operator
db.collection_name.aggregate(
[
{$unwind: "$photos"},
{$match: {"photos.isPrivate": false}},
{$group: {"_id": {"id": "$_id", "user": "$user"}, photos: {$push: "$photos"}}}
{$project: {"_id": "$_id.id", "user": "$_id.user", "photos": 1, "_id": 0 }}
]
)

Answer 2

You can use $elemMatch to the result projection like this
db.collection_name.find(
{ photos:{ $elemMatch:{isPrivate: false} } }, //1
{photos:{$elemMatch:{isPrivate: false}}}) //2
Find all documents that have at least a photo which is not private
Select only photos that are not private for the documents found.