How to query nested document in mongodb?

Question

I have document with nested document reviews:

{
        "_id" : ObjectId("53a5753937c2f0ef6dcd9006"),
        "product" : "Super Duper-o-phonic",
        "price" : 11000000000,
        "reviews" : [
                {
                        "user" : "fred",
                        "comment" : "Great!",
                        "rating" : 5
                },
                {
                        "user" : "Tom",
                        "comment" : "Great again!",
                        "rating" : 5
                },
                {
                        "user" : "Tom",
                        "comment" : "I agree with fred somewhat",
                        "rating" : 4
                }
        ]
}

I want to find only those reviews whose rating is 5.

Final query should select product price and two documents from reviews whose rating is 5.

The last query I tried is :

db.testData.find({'reviews':{$elemMatch:{'rating':{$gte:5}}}}).pretty()

It's strange but it doesn't work.

How to do this in mongodb?

JohnnyHK · Accepted Answer · 2014-06-21 15:07:48Z

4

If you only want a single sub-doc from reviews whose rating is 5, you can use the $ positional projection operator to include the first element of reviews that matches your query:

db.test.find({'reviews.rating': 5}, {product: 1, price: 1, 'reviews.$': 1})

If you want all reviews elements with a rating of 5 (instead of just the first) you can use aggregate instead of find:

db.test.aggregate([
    // Only include docs with at least one 5 rating review
    {$match: {'reviews.rating': 5}}, 
    // Duplicate the docs, one per reviews element
    {$unwind: '$reviews'}, 
    // Only include the ones where rating = 5
    {$match: {'reviews.rating': 5}}, 
    // Only include the following fields in the output
    {$project: {product: 1, price: 1, reviews: 1}}])

edited Jun 21, 2014 at 15:07

answered Jun 21, 2014 at 14:39

JohnnyHK

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2 Comments

Volodymyr Levytskyi Over a year ago

I just tried this and it doesn't work if I select two documents from reviews with rating 5. because reviews.$ ensures that only the first matching document is included in result.

JohnnyHK Over a year ago

@VolodymyrLevytskyi Use the aggregate approach if you want to include all rating 5 reviews instead of just the first one.

Community · Accepted Answer · 2017-05-23 10:27:04Z

0

Take a look up here: MongoDB - how to query for a nested item inside a collection?

Just in case you thought about this: If you try to accomplish this with $elemMatchit will jsut return the first matching review. http://docs.mongodb.org/manual/reference/operator/projection/elemMatch/

edited May 23, 2017 at 10:27

CommunityBot

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answered Jun 21, 2014 at 14:09

Zarathustra

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1 Comment

Volodymyr Levytskyi Over a year ago

I tried $elemMatch and it doesn't work. Can you post a query?

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