在mongodb聚合中查找


问题内容

以下bson是personaddresscollection:

{ 
        "id" : "123456", 
        "name" : "foo", 
        "address" : [
            {
                "local" : "yes", 
                "location" : [
                   {
                        "place" : {
                            "_id":"VZG",

                        }, 
                        "place_lat" : "18", 
                        "place_lan" : "83",

                },
                {
                        "place" : {
                            "name" : "kerala", 
                            "district" : "palakkad", 
                            "pincode" : "5203689",

                        }, 
                        "place_lat" : "18", 
                        "place_lan" : "83",      
                    }
                ]
            }
        ]
    }

我还有另一个places收藏:

 {
     "_id":"VZG",
     "name" : "vizag", 
     "district" : "Visakhaptanam, 
     "pincode" : "568923",
 }

MongoDB中聚集使用查找,我想嵌入 places 在收集personaddress集合

我尝试使用

Aggregation aggregation = newAggregation(lookup("places", "address.location.place._id", "_id", "myplaces"), unwind("myplaces"));

AggregationResults<OutputDocument> aggResults = mongoTemplate.aggregate(aggregation, PersonAddressDocument.class, OutputDocument.class);

谁能帮我?


问题答案:

由于您具有嵌套数组,因此需要首先应用
$unwind
运算符,以便在使用
$lookup
管道之前对嵌入的文档进行反规范化(除非您已经在聚合操作中对其进行了展平):


db.personaddress.aggregate([
    { "$unwind": "$address" },
    { "$unwind": "$address.location" },
    {
        "$lookup": {
            "from": "places", 
            "localField": "address.location.place._id", 
            "foreignField": "_id", 
            "as": "address.location.place", 
        }
    }
])

然后可以实现为(未试用):

LookupOperation lookupOperation = LookupOperation.newLookup()
    .from("places")
    .localField("address.location.place._id")
    .foreignField("_id")
    .as("address.location.place");

Aggregation agg = newAggregation(
    unwind("address"),
    unwind("address.location"),
    lookupOperation  
);

AggregationResults<OutputDocument> aggResults = mongoTemplate.aggregate(
    agg, PersonAddressDocument.class, OutputDocument.class
);

如果您的Spring Data版本不支持此功能,则一种解决方法是实施
AggregationOperation
接口以接受DBObject

public class CustomGroupOperation implements AggregationOperation {
    private DBObject operation;

    public CustomGroupOperation (DBObject operation) {
        this.operation = operation;
    }

    @Override
    public DBObject toDBObject(AggregationOperationContext context) {
        return context.getMappedObject(operation);
    }
}

然后
$lookup

在聚合管道中将操作实现为DBObject:

DBObject lookupOperation = (DBObject)new BasicDBObject(
    "$lookup", new BasicDBObject("from", "places")
        .append("localField", "address.location.place._id")
        .append("foreignField", "_id")
        .append("as", "address.location.place")       
);

然后可以将其用作:

Aggregation agg = newAggregation(
    unwind("address"),
    unwind("address.location"),
    lookupOperation  
);

AggregationResults<OutputDocument> aggResults = mongoTemplate.aggregate(
    agg, PersonAddressDocument.class, OutputDocument.class
);