How to get just element of array in Java & MongoDB?

Question

This is my example for Product MongoDB Collection:

product {

sku: abcQWE123,
url: www.xyz.com
comments:[
    "Lorem ipsum dolor sit amet",
    "inceptos himenaeos",
    "viverra. Aenean placerat ex in justo ul"
]

}

I want to get just a comment with "url" if it consist "ipsum".

Imagine that if database had a just entry which is above, my result would have been like this:

product{

url: www.xyz.com
comments:[
    "Lorem ipsum dolor sit amet",
]

}

I can get whole entries which contain "ipsum", using commands at below. But I want to be specific although I don't know how to do it. Could you help me about this subject?

public void main(String[] args) {

    MongoCursor<Product> p = mongoDB.getProducts().find(myMongoFilter("comments", "ipsum")).iterator();
    
    try {
        while (p.hasNext()) {
            System.out.println(p.next().toString());
        }
    } finally {
        p.close();
    }

}

public Document myMongoFilter(String myField, String myRegex) {
    return new Document(myField, new Document("$regex", myRegex));
}

You need the comments with "impsum" in it and the respective URL?? — Karan Gaur
– Karan Gaur, Commented Jun 8, 2021 at 16:44

E G · Accepted Answer · 2021-06-11 13:56:23Z

Here is the my answer. @Sumanth229 thank you for mentioning the algorithm.

public static void main(String[] args) {
    ...
    ...
    List<Document> products = mongoDB.getProductsInRaw().aggregate(Filter.findComments("ipsum")).into(new ArrayList<>());

    products.forEach(document -> System.out.println(document.toJson()));
    ...
    ...
}

public MongoCollection<Products> getProducts() {
    return getDB().getCollection("products", Products.class);
}

public MongoCollection<Document> getProductsInRaw() {
    return getDB().getCollection("products");
}

public static ArrayList<Bson> findComments(String keywords) {
    ArrayList<Bson> queries = new ArrayList<>();
    queries.add(Filter.aggregateContains("comments", keywords));
    queries.add(Filter.aggregateUnwind("comments"));
    queries.add(Filter.aggregateContains("comments", keywords));

    //
    // To access full question's answer, remove comment block.
    // I don't want to use this line because of my requests were changed.
    // queries.add(new Document("$group", new Document("_id", new Document("comments", "$comments").append("url", "$url")).append("count", new Document("$sum", 1))));
    //
    //

    return queries;
}

public static Document aggregateContains(String field, String regex) {
    return new Document("$match", new Document(field, new Document("$regex", regex)));
}

public static Document aggregateUnwind(String field) {
    return new Document("$unwind", "$" + field);
}

Herman Bovens · Accepted Answer · 2021-06-10 06:44:39Z

0

You can filter like this using projections in mongo

import com.mongodb.client.model.Projections;

MongoCursor<Product> p = mongoDB.getProducts()
                                .find(myMongoFilter("comments", "ipsum"))
                                .projection(Projections.include("comments", "url"))
                                .iterator();

edited Jun 10, 2021 at 6:44

Herman Bovens

12.5k5 gold badges50 silver badges64 bronze badges

answered Jun 8, 2021 at 17:05

Sumanth229

542 bronze badges

3 Comments

E G Over a year ago

Hi, your contribution does not working totally what I want to see. Yes, it masks the SKU field, but other comments do not go anywhere.

Sumanth229 Over a year ago

you have to unwind the comments list and then filter and group it back using MongoDB aggregation to show only the comments with ipsum in it.

E G Over a year ago

If you have a code-solution, could you share with me? By the way, thank you for sharing algorithm, I am going to searching it that how to do it.

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