如何使用MongoDB 3.0 Java驅動程序執行聚合

Question

我正在嘗試使用MongoDB Java驅動程序（3.0）執行簡單的聚合操作。 需要有關如何使用JAVA API編寫以下mongo shell查詢的幫助。

db.coll.aggregate([
    { $project: {
        email_id: { $ifNull: [ "$email_id", " " ] },
        phone_num: { $ifNull: [ "$phone_num","NA" ] },
        id : 1,
        firstname :1,
        lastname :1,
        status : 1
        }
    },
    { $match: { status: "true"} },
    { "$group": {
        "_id": "$id",
        "details": { "$push": {
            "$concat": [ "$firstname", " ", "$lastname", " | ", "$email_id" , " | ", "$phone_num" ]
        }}
    }}
])

Answer 1

這是您的shell查詢的Java驅動程序查詢

MongoClient mongo = new MongoClient();    
MongoDatabase database = mongo.getDatabase("your_database");
        Document emailIdDoc = new Document("$ifNull",Arrays.asList("$email_id", " "));
        Document phoneNumDoc = new Document("$ifNull", Arrays.asList("$phone_num", "NA")); 
        Document projectDoc = new Document("$project" , new Document("email_id", emailIdDoc).append("phone_num", phoneNumDoc).append("id" , 1).append("firstname" , 1).append("lastname", 1).append("status", 1));
        Document matchDoc = new Document("$match", new BasicDBObject("status", "true"));
        Document groupDoc = new Document("$group", new Document("_id", "$id").append("details", new Document("$push", concat)));
        AggregateIterable<Document> aggregationResult = db.getCollection("your_collection").aggregate(asList(projectDoc, matchDoc, groupDoc));

使用不推薦使用的方法

MongoClient mongo = new MongoClient();
    DB db = mongo.getDB("your_database");
    BasicDBObject emailId = new BasicDBObject("$ifNull",Arrays.asList("$email_id", " "));
    BasicDBObject phoneNum = new BasicDBObject("$ifNull", Arrays.asList("$phone_num", "NA"));
    DBObject project = new BasicDBObject("$project" , new BasicDBObject("email_id", emailId).append("phone_num", phoneNum).append("id" , 1).append("firstname" , 1).append("lastname", 1).append("status", 1));
    DBObject match = new BasicDBObject("$match", new BasicDBObject("status", "true")); 
    DBObject concat = new BasicDBObject("$concat", Arrays.asList( "$firstname", " ", "$lastname", " | ", "$email_id" , " | ", "$phone_num"));
    Document concatDoc = new Document("$concat", Arrays.asList( "$firstname", " ", "$lastname", " | ", "$email_id" , " | ", "$phone_num"));
    DBObject group = new BasicDBObject("$group", new BasicDBObject("_id", "$id").append("details", new BasicDBObject("$push", concat)));

    AggregationOutput iterable = db.getCollection("your_collection").aggregate(project, match, group);