java – MongoDB中计算的group-by字段

Aggregation agg = newAggregation(
        project("quantity")
            .andExpression("dayOfMonth(date)").as("day")
            .andExpression("month(date)").as("month")
            .andExpression("year(date)").as("year")
            .andExpression("price * quantity").as("totalAmount"),group(fields().and("day").and("month").and("year"))
            .avg("quantity").as("averavgeQuantity")
            .sum("totalAmount").as("totalAmount")
            .count().as("count")
    );

就像我所说的,反直觉,你应该能够宣布所有这些在$group阶段,但帮助者似乎不这样工作.序列化有点有趣(用数组包装日期操作符参数),但它似乎工作.但是,这是两个管道阶段,而不是一个.

这是什么问题？通过分阶段,“项目”部分强制处理流水线中的所有文档,以获得计算的字段,这意味着它在移动到组阶段之前通过所有的阶段.

通过以两种形式运行查询可以清楚地看到处理时间的差异.在单独的项目阶段,我的硬件执行时间要比在“组”操作期间计算所有字段的查询多三倍.

所以现在看来??唯一正确的方法是通过自己建立管道对象：

ApplicationContext ctx =
            new AnnotationConfigApplicationContext(SpringMongoConfig.class);
    MongoOperations mongoOperation = (MongoOperations) ctx.getBean("mongoTemplate");

    BasicDBList pipeline = new BasicDBList();
    String[] multiplier = { "$price","$quantity" };

    pipeline.add(
        new BasicDBObject("$group",new BasicDBObject("_id",new BasicDBObject("month",new BasicDBObject("$month","$date"))
                    .append("day",new BasicDBObject("$dayOfMonth","$date"))
                    .append("year",new BasicDBObject("$year","$date"))
            )
            .append("totalPrice",new BasicDBObject(
                "$sum",new BasicDBObject(
                    "$multiply",multiplier
                )
            ))
            .append("averageQuantity",new BasicDBObject("$avg","$quantity"))
            .append("count",new BasicDBObject("$sum",1))
        )
    );

    BasicDBObject aggregation = new BasicDBObject("aggregate","collection")
        .append("pipeline",pipeline);

    System.out.println(aggregation);

    CommandResult commandResult = mongoOperation.executeCommand(aggregation);

或者如果所有这些似乎都简化了,那么你可以随时使用JSON源并解析.但当然,它必须是有效的JSON：

String json = "[" +
        "{ "$group": { "+
            ""_id": { " +
                ""month": { "$month": "$date" }," +
                ""day": { "$dayOfMonth":"$date" }," +
                ""year": { "$year": "$date" } " +
            "}," +
            ""totalPrice": { "$sum": { "$multiply": [ "$price","$quantity" ] } }," +
            ""averageQuantity": { "$avg": "$quantity" }," +
            ""count": { "$sum": 1 } " +
        "}}" +
    "]";

    BasicDBList pipeline = (BasicDBList)com.mongodb.util.JSON.parse(json);