Mongodb : find matching elements in an array with given attributes using java driver

Question

Trying to migrate my game to mongodb (linux-i686-2.4.6) but so far having a lot of struggle :( one is that; I have a collection named gamesTable with the following elements below and I want to make a search in playerHistories array.

{
"_id": {
    "$oid": "52307b8fe4b0fc612dea2c70"
},
"id": "52307b8fe4b0fc612dea2c70", "name": "poker", "initTime": 1378909071070, "startTime": 1378909071098, "endTime": 1378909071134,
"playerHistories": [
    {
        "playerId": "52307b8fe4b0fc612dea2c6e",
        "time": 1378909071098,
        "event": "EnteredGame"
    } ,
    {
        "playerId": "52307b8fe4b0fc612dea2c6f",
        "time": 1378909071098,
        "event": "EnteredGame"
    } ,
    {
        "playerId": "52307b8fe4b0fc612dea2c6f",
        "time": 1378909071117,
        "event": "LostGame"
    } ,
    {
        "playerId": "52307b8fe4b0fc612dea2c6e",
        "time": 1378909071128,
        "event": "WonGame"
    }
]
},
{
"_id": {
    "$oid": "52307b8fe4b0fc612dea2c71"
}, "id": "52307b8fe4b0fc612dea2c71", "name": "poker", "initTime": 1378909071150, "startTime": 1378909071165, "endTime": 1378909071189,
"playerHistories": [
    {
        "playerId": "52307b8fe4b0fc612dea2c6e",
        "time": 1378909071165,
        "event": "EnteredGame"
    } ,
    {
        "playerId": "52307b8fe4b0fc612dea2c6f",
        "time": 1378909071165,
        "event": "EnteredGame"
    } ,
    {
        "playerId": "52307b8fe4b0fc612dea2c6e",
        "time": 1378909071176,
        "event": "LostGame"
    } ,
    {
        "playerId": "52307b8fe4b0fc612dea2c6f",
        "time": 1378909071183,
        "event": "WonGame"
    }
]
}

and I want to find games won by a player, in our example it is;

{ "playerHistories.playerId" : "52307b8fe4b0fc612dea2c6f" , "playerHistories.event" : "WonGame"}}

I read that I should use $elemMatch for matching elements in an array however it returns nothing :(

here is the code I use

    BasicDBObject elemMatch = new BasicDBObject();
    elemMatch.put("playerHistories.playerId", player1.getId());
    elemMatch.put("playerHistories.event", "WonGame");
    BasicDBObject foo = new BasicDBObject();
    foo.put("$elemMatch", elemMatch);
    gamesTable.find(foo);

What am I doing wrong?

hevi · Accepted Answer · 2013-09-12 07:57:10Z

5

thanks to parvin I find it out changing his solution.

    DBObject statusQuery = new BasicDBObject("event", "WonGame");
    statusQuery.put("playerId", "52307b8fe4b0fc612dea2c6f");
    DBObject fields = new BasicDBObject("$elemMatch", statusQuery);
    DBObject query = new BasicDBObject("playerHistories",fields);
    gamesTable.find(query);

answered Sep 12, 2013 at 7:57

hevi

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Parvin Gasimzade · Accepted Answer · 2013-09-11 14:48:15Z

2

You can do it as follows :

        DBObject query = new BasicDBObject("playerHistories.playerId", "52307b8fe4b0fc612dea2c6f");

        DBObject statusQuery = new BasicDBObject("event", "WonGame");
        DBObject elemMatchQuery = new BasicDBObject("$elemMatch", statusQuery);

        DBObject fields = new BasicDBObject();
        fields.put("playerHistories", elemMatchQuery);
        fields.put("initTime", 1);
        fields.put("startTime", 1);
        fields.put("endTime", 1);

        DBCursor cur = coll.find(query, fields);

answered Sep 11, 2013 at 14:48

Parvin Gasimzade

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2 Comments

hevi Over a year ago

no luck, returns all the elements. I am not sure if you wrote DBObject statusQuery = new BasicDBObject("event", "WonGame"); intentionally or you just missed that 'event' is also a member of an object in the array.

Parvin Gasimzade Over a year ago

It is written intentionally. I have inserted same data on my local machine and everything works fine for me. It should project the results that matched with the given query.Most probably you missed something. Check it again.

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