MongoDB Java查找文檔並過濾數組字段（刪除不符合條件的數組數據）

Question

我嘗試請求一個Collection，但是無法過濾嵌入式數組。 我想獲取集合中所有匹配{“ players.nick”：nick}的文檔，並過濾'players'數組以僅獲取搜索到的玩家。

這是初始文件：

{"_id":2000,"type":3,"prizepool":6520.5,"name":"XXX","start":1515701700,"end":1515719580,"buyin":2.25,"rake":0.5,"prize":0,"bounty":2.25,"players":[{"nick":"player1","rank":1,"cash":660.85,"kill":468.64,"ticket":0,"reentry":0},{"nick":"player2","rank":2,"cash":430.35,"kill":101.31,"ticket":0,"reentry":0},{"nick":"player3","rank":3,"cash":312.98,"kill":72.26,"ticket":0,"reentry":0},{"nick":"player4","rank":4,"cash":237.99,"kill":27.15,"ticket":0,"reentry":1}]}

在請求后，我想檢索：

{"_id":2000,"type":3,"prizepool":6520.5,"name":"XXX","start":1515701700,"end":1515719580,"buyin":2.25,"rake":0.5,"prize":0,"bounty":2.25,"players":[{"nick":"player1","rank":1,"cash":660.85,"kill":468.64,"ticket":0,"reentry":0}}

有誰知道如何用Java方式做到這一點？

謝謝 ！

Answer 1

您可以在Java中使用以下聚合管道。

MongoClient mc = new MongoClient();
MongoDatabase db = mc.getDatabase(db);
MongoCollection col = db.getCollection(col);

對於單場比賽，您可以使用$elemMatch投影

col.find().projection(Projections.fields(Projections.include("_id","type", "prizepool","name","start","end","buyin","rake","prize","bounty"),
                Projections.elemMatch("players", Filters.eq("nick", "player1"))));

對於單場和多場比賽

Bson filter = new Document("players", Document.parse("{\n" +
            "            $filter: {\n" +
            "               input: \"$players\",\n" +
            "               as: \"player\",\n" +
            "               cond: { $eq: [ \"$$player.nick\", \"player1\" ] }\n" +
            "            }\n" +
            "         }"));
Bson addFields = new Document("$addFields", filter);
col.aggregate(Arrays.asList(addFields));