MongoDB, Java - From JSON Query to Document

Question

Hy,

I need some help translating the following MongoDB Query into MongoDB Java driver query.

Please be advised that the query works.

db.days.aggregate([
    { $match: { 'day' : 'March_1'}},
    { $project: {
        _id : 0,
        day: 1,
        events: {$filter: {
            input: '$events',
            as: 'event',
            cond: {$eq: ['$$event.year', '2002']}
        }}
    }}
])

My try is this, but it failed and I need your help.

Document query = new Document("$match", new Document("day", day)).
    append("$project", new Document("_id", 0).
            append("day", 1).
            append("events", new Document("$filter", new Document(
                    "input", "$" + category).
                    append("as", "event").
                    append("cond", new Document("$eq", Arrays.asList("$$event.year", year))))));

The error that I am getting is

"{ "ok" : 0.0, "errmsg" : "A pipeline stage specification object must contain exactly one field.", "code" : 16435 }"

Thank you very much!

The problem that I think it is is that I build a document instead of an array. But I could not find anything that build an array using Documents. — Petru Daniel Tudosiu
– Petru Daniel Tudosiu, Commented Apr 5, 2016 at 10:38

zeugor · Accepted Answer · 2016-04-05 10:47:11Z

5

Don't place the $match and $project in the same object, use a list

AggregateIterable<Document> iterable = collection.aggregate(
  asList(
    new Document("$match", new Document("day", day)),
    new Document("$project", 
        new Document("_id", "0")
            .append("day", 1)
            .append(
                "events", 
                new Document(
                    "$filter",
                    new Document("input", "$events")
                        .append("as", "event")
                        .append(
                            "cond", 
                            new Document("eq", Arrays.asList("$$event.year", year))
                        )
                )
            )
    )
   )
)

edited Apr 5, 2016 at 10:47

answered Apr 5, 2016 at 10:42

zeugor

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1 Comment

Petru Daniel Tudosiu Over a year ago

Thank you very much! I just started using MongoDB a few days ago and I am going to kill myself with Java...

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