Question

我正在使用mongodb的spring数据，我在MongoDB中有一个c_user集合，如下所示：

db.c_user.find().pretty();

{
        "_id" : "user-1",
        "journeys" : [
            {
                "fromStation" : "A",
                "toStation" : "B"
            },
            {
                "fromStation" : "B",
                "toStation" : "C"
            },
            {
                "fromStation" : "A",
                "toStation" : "D"
            }
        ]
    },
    {
        "_id" : "user-2",   
        "journeys" : [
            {
                "fromStation" : "A",
                "toStation" : "B"
            },
            {
                "fromStation" : "B",
                "toStation" : "C"
            },
            {
                "fromStation" : "D",
                "toStation" : "E"
            }
        ]
    }

我想要的是获取匹配'journeys.fromStation'==“A”的c_user文档列表。因此，如果您在mongo shell中运行以下查询：

db.c_user.runCommand({ 
   "aggregate" : "c_user" , 
   "pipeline" : [ { "$match" : { "journeys.fromStation" : "A"}} , 
                  { "$unwind": "$journeys"} , 
                  { "$match" : { "journeys.fromStation" : "A"}}
                ]
});

我得到了c_user文档列表，这是我所期望的：

{
    "_id" : "user-1",
    "journeys" : [
        {
            "fromStation" : "A",
            "toStation" : "B"
        },
        {
            "fromStation" : "A",
            "toStation" : "D"
        }
    ]
},
{
    "_id" : "user-2",   
    "journeys" : [
        {
            "fromStation" : "A",
            "toStation" : "B"
        }
    ]
}

}

现在我需要使用spring数据mongo聚合执行此操作：

TypedAggregation<CUser> aggregation = newAggregation(CUser.class,
                match(where("journeys.fromStation").is("A")),
                unwind("journeys"),
                match(where("journeys.fromStation").is("A")));

        AggregationResults<CUser> results = mongoTemplate.aggregate(aggregation, CUser.class);

        return results.getMappedResults();

执行此操作时，我收到此错误：

org.springframework.data.mapping.model.MappingInstantiationException: 
Failed to instantiate java.util.List using constructor NO_CONSTRUCTOR with arguments

显然它是一个无法实例化的List.class。似乎返回的对象是BasicDbLIst。

无论如何，那么如何获得与mongo shell相同的结果呢？即作为List<CUser>

任何帮助表示赞赏...

此致 GM

Spring Data MongoDB Aggregation elemMatch

0 个答案: