Question

我在Java中使用Morphia和MongoDB，我喜欢在聚合查询中获得许多记录：

AggregationPipeline pipCount = ds.createAggregation(MyTable.class)
            .match(query1)
            .match(query2)
            .unwind("transactions")
            .match(query3)
            .group("_id", grouping("_id"), grouping("count", new Accumulator("$sum", 1)));
Iterator<MyTable> result = pipCount.aggregate(MyTable.class);

我需要使用分组（“_ id”）来删除重复的结果，然后计算结果，但找不到任何方法来读取和值... 任何的想法？

示例数据：

{
    "_id": "00000222",
    "create_date": ISODate("2015-05-06T07:20:31.000+0000"),
    "update_date": ISODate("2015-05-06T07:20:31.000+0000"),
    "payment": 70.0,
    "fee": 0.0,
    "type": "RECURRING",
    "currency": "USD",
    "status": "OK",
    "transactions": [{
        "_id": "111111223",
        "amount": 1260.0,
        "fee_type": "VARIABLE_ADD",
        "fee_rate": 2.75,
        "status": "ERROR",
        "charges": [{
            "_id": "2222223344",
            "amount": 1000.0,
            "recurring": true,
            "firstTime": false,
            "oneTime": true,
        }, {
            "_id": "222222222233221",
            "amount": 70.0,
            "recurring": true,
            "firstTime": true,
            "oneTime": true,
        }]
    }],
    "users": {
        "_id": "33333333332212",
        "update_date": ISODate("2015-12-18T08:03:35.000+0000"),
        "user_id": "sdjfhsd@skjksdf.com",
        "first_name": "dsjfj",
        "last_name": "skdfjf",
    }
}

结果：1

Answer 1

你可以尝试这样的事情。你不需要额外的分组。第一组将在计算总和时计算重复项并计算计数并将响应映射到文档并读取计数。

import org.bson.Document; 

AggregationPipeline pipCount = datastore.createAggregation(MyTable.class)
            .match(query1)
            .match(query2)
            .unwind("somethingID")
            .match(query3)
            .group("_id", grouping("count", new Accumulator("$sum", 1)))
            .project(Projection.projection("count"));

    Iterator<Document> result = pipCount.aggregate(Document.class);

    while (result.hasNext()) {
        Document document = result.next();
        Integer count = document.getInteger("count");
    }

如何在mongoDB中使用morphia获取累加器结果？

1 个答案: