在 mongodb 聚合中查找答案

【问题标题】：lookup in mongodb aggregation在 mongodb 聚合中查找
【发布时间】：2017-05-05 18:05:12
【问题描述】：

以下bson为personaddress集合：

{ 
        "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",      
                    }
                ]
            }
        ]
    }

我还有一个places 收藏：

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

在 mongodb 聚合中使用查找，我想将 places 集合嵌入到 personaddress 集合中

我尝试过使用

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

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

谁能帮帮我？

【问题讨论】：

标签： java mongodb spring-mvc mongodb-query aggregation-framework

【解决方案1】：

由于您有嵌套数组，因此您需要先应用 $unwind 运算符，以便在使用 $lookup 管道之前对嵌入的文档进行非规范化（除非您已经在您的聚合操作中将它们展平）：

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（未经测试）：

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，解决方法是实现 AggregationOperation 接口以接收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);
    }
}

然后将$lookup操作实现为聚合管道中的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")       
);

然后您可以将其用作：

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

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

【讨论】：

非常感谢

【解决方案2】：

db.productgroups.aggregate([
    // Unwind the source
    { "$unwind": "$products" },
    // Do the lookup matching
    { "$lookup": {
       "from": "products",
       "localField": "products",
       "foreignField": "_id",
       "as": "productObjects"
    }},
    // Unwind the result arrays ( likely one or none )
    { "$unwind": "$productObjects" },
    // Group back to arrays
    { "$group": {
        "_id": "$_id",
        "products": { "$push": "$productObjects" },
    }}
])

【讨论】：