MongoDB / Java-如何在Java中为mongodb实现$ out [英] MongoDB/Java - How implement $out in java for mongodb

问题描述

我有一个aggregate（）查询，其结果数据超过16Mb。为了处理16Mb问题，他们提供了以下内容。

I have a aggregate() query which results data more than 16Mb. To work with 16Mb issue they provided something like below.

{$out : "datasetTemp"}
 // datasetTemp name of collection.

我在MongoDB shell中尝试了以下操作。

I have tried following in MongoDB shell it working.

db.dataset.aggregate([ { $match : {isFlat : true}}, {$out : "datasetTemp"}])

但是我需要使用管道使用java-mongodb来实现。

But I need to do it with java-mongodb using pipeline.

这是原始代码的一部分

dbObjArray = new BasicDBObject[2]
dbObjArray[0]= cruxLevel
dbObjArray[1] = project
//dbObjArray[2] = out
List<DBObject> pipeline = Arrays.asList({dbObjArray})
output= dataset.aggregate(pipeline)

我尝试了这不起作用（无法创建集合）

I tried this which is not working (collection is not getting created)

dbObjArray = new BasicDBObject[2]
dbObjArray[0]= cruxLevel
dbObjArray[1] = project
//dbObjArray[2] = out
List<DBObject> pipeline = Arrays.asList({dbObjArray},{$out:"datasetTemp"})
output= dataset.aggregate(pipeline)

不创建集合时不会抛出任何错误。

Which is not throwing any error not creating collection.

我也尝试过此操作

                 DBObject out = new BasicDBObject('$out', "temp_colls");
                 dbObjArray = new BasicDBObject[2]
                 dbObjArray[0]= cruxLevel
                 dbObjArray[1] = project
                // dbObjArray[2] = out
                 List<DBObject> pipeline = Arrays.asList({dbObjArray})
                 if (!datasetObject?.isFlat && jsonFor != 'collection-grid') {
                     //mongoPipeline = new AggregateArgs (Pipeline = pipeline, AllowDiskUse = true, OutputMode = AggregateOutputMode.Cursor)
                     output= dataSetCollection.aggregate(pipeline,out)
                     DBCollection tempColl =  dataBase.getCollection("temp_colls")
                     def cursor = tempColl.find();
                     try {
                         while(cursor.hasNext()) {
                             System.out.println(cursor.next());
                         }
                     } finally {
                         cursor.close();
                     }
                     output = cursor
                 }else{
                     output= dataSetCollection.aggregate(project)
                 }                  
                 output.results().eachWithIndex{list,index->
                 dataList.add(output.results()[index])
                }                   

将其抛出以下错误。

com.mongodb.CommandFailureException: { "serverUsed" : "127.0.0.1:15847" , "errmsg" : "exception: aggregation result exceeds maximum document size (16MB)" , "code" : 16389 , "ok" : 0.0}

在这种情况下如何使用 $ out 。

How use $out under this scenario.

谢谢。

推荐答案

您可能想尝试一下：

public class JavaAggregation {
    public static void main(String args[]) throws UnknownHostException {

        MongoClient mongo = new MongoClient();
        DB db = mongo.getDB("databaseName");

        DBCollection coll = db.getCollection("dataset");

        /*
            MONGO SHELL : 
            db.dataset.aggregate([ 
                { "$match": { isFlat : true } }, 
                { "$out": "datasetTemp" }
            ])
        */

        DBObject match = new BasicDBObject("$match", new BasicDBObject("isFlat", true)); 
        DBObject out = new BasicDBObject("$out", "datasetTemp"); 

        AggregationOutput output = coll.aggregate(match, out);

        DBCollection tempColl = db.getCollection("datasetTemp");
        DBCursor cursor = tempColl.find();

        try {
            while(cursor.hasNext()) {
                System.out.println(cursor.next());
            }
        } finally {
            cursor.close();
        }
    }
}

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