如何在 Java 和 MongoDB 中获取数组的元素？

Question

这是我的 Product MongoDB 集合示例：

product {

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

}

如果包含“ipsum”，我只想获得带有“url”的评论。

想象一下，如果数据库有一个上面的条目，我的结果会是这样的：

product{

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

}

我可以使用下面的命令获取包含“ipsum”的整个条目。但我想具体一点，虽然我不知道该怎么做。你能帮我解决这个问题吗？

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));
}

Answer 1

这是我的答案。 @Sumanth229 感谢您提及算法。

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);
}

Answer 2

您可以使用 mongo 中的投影进行这样的过滤

import com.mongodb.client.model.Projections;

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