Filtering nested array in Mongo Java driver

Question

Following NoSQL query returns all reviews of a particular user :

db.getCollection('catalog-review').aggregate([
{
     $project: {
       reviews: {
         $filter: {
           input: "$reviews",
           as: "review",
           cond: { $eq: [ "$$review.userId", 121 ] }
          }
        }
      }
}
])

This is query works fine but if I implement this in Java using Mongo driver, the "$$" doesn't work.

List<CatalogReview> reviews = collection.aggregate(Arrays.asList(
            new Document("$project", new Document("reviews", new Document("$filter", new Document("input", "$reviews")
                    .append("as", "review").append("cond", new Document("$eq", Arrays.asList(new Document("$$review.userId", 121)))))))
    )).into(new ArrayList<>());

The error message:

com.mongodb.MongoCommandException: Command failed with error 15999: 'invalid operator '$$review.userId'' on server localhost:27017. The full response is { "ok" : 0.0, "errmsg" : "invalid operator '$$review.userId'", "code" : 15999 }

Does Mongo driver supports aggregate functions ?

4J41 · Accepted Answer · 2016-10-12 16:19:05Z

3

The problem is Arrays.asList(new Document("$$review.userId", 121)). It should be Arrays.asList("$$review.userId", 121).

Arrays.asList(new Document("$$review.userId", 121)) = [ { "$$review.userId" : 121 } ]

Arrays.asList("$$review.userId", 121) = [ "$$review.userId", 121 ]

The snippet should be like below:

List<CatalogReview> reviews = collection.aggregate(Arrays.asList(
            new Document("$project", new Document("reviews", new Document("$filter", new Document("input", "$reviews")
                    .append("as", "review").append("cond", new Document("$eq", Arrays.asList("$$review.userId", 121))))))
    )).into(new ArrayList<>());

answered Oct 12, 2016 at 16:19

4J41

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1 Comment

FarthVader Over a year ago

Works like a charm ! Thank you.

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