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.

Answer 1

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.