Mongo DB regex aggregation query using java API

Question

I want to query using regex and aggregation in mongo db, the following is working fine in mongo shell but how to write the same using Java API.

    db.posts_collection.aggregate({$unwind:"$posts"},
    {$match :{"posts.message":/.*keyword.*/} })

I tried using the following but unable to get the required result,

    BasicDBObject unwind = new BasicDBObject("$unwind","$posts");
    BasicDBObject matchKeyWord = new BasicDBObject("$match",new
    BasicDBObject("posts.message",java.util.regex.Pattern.compile("keyword")));
    AggregationOutput output = collection.aggregate(unwind,matchKeyWord);

Please tell me how to write the same query in java.

Then what results do you get?

Philipp
– Philipp

2014-06-21 10:10:18 +00:00
Commented Jun 21, 2014 at 10:10 — Philipp
– Philipp, Commented Jun 21, 2014 at 10:10

Neil Lunn · Accepted Answer · 2014-06-21 10:23:48Z

2

I would think that should work, but if you really wanted to be sure use the $regex operator form instead:

    BasicDBObject unwind = new BasicDBObject("$unwind","$posts");
    BasicDBObject matchKeyWord = new BasicDBObject(
        "$match",new BasicDBObject(
            "posts.message",new BasicDBObject("$regex",".*keyword.*")
        )
    );
    AggregationOutput output = collection.aggregate(unwind,matchKeyWord);

That operator exists for the purpose of "safe" serialization with differing drivers.

answered Jun 21, 2014 at 10:23

Neil Lunn

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