使用MongoDB的MapReduce Java驱动程序错误的BSONElement断言类型错误 [英] MapReduce using MongoDB Java Driver failes with wrong type for BSONElement assertion

问题描述

我是MongoDB和MapReduce的新手。我需要在我的数据库中的集合上做一些MapReduce。 MAP 和 REDUCE_MAX 函数有效，因为我能够在Mongo交互式shell中完成我的需求（v.1.8） 0.2）。但是，我尝试使用Mongo Java驱动程序（v.2.6.3）执行相同的操作时出错

I'm pretty new to MongoDB and MapReduce. I need to do some MapReduce on a collection in my DB. The MAP and REDUCE_MAX functions work, since I was able to accomplish my needs in the Mongo interactive shell (v.1.8.2). However, I get an error trying to perform the same thing using the Mongo Java Driver (v. 2.6.3)

我的 MAP 和 REDUCE_MAX 函数如下所示：

String MAP =
            "function(){" +
                    "if(this.type != \"checkin\"){return;}" +
                    "if(!this.venue && !this.venue.id){return;}" +
                    "emit({userId:this.userId, venueId:this.venue.id}, {count:1});" +
                    "};";


String REDUCE_MAX =
            "function(key, values){" +
                    "var res = {count:0};" +
                    "values.forEach(function(value){result.count += value.count;});" +
                    "return res;" +
                    "};";

这是我正在执行的命令：

This is the command I'm executing:

MapReduceOutput sum = collection
                .mapReduce(MAP, REDUCE_MAX, null, null);

这是我得到的错误：

com.mongodb.CommandResult$CommandFailure: command failed [command failed [mapreduce] { "assertion" : "wrong type for BSONElement (replace) 10 != 2" , "assertionCode" : 13111 , "errmsg" : "db assertion failure" , "ok" : 0.0}

我不知道知道哪个BSONElement的类型错误。我已经用Google搜索了 assertionCode：13111 。我还检查了MongoDB日志，但没有找到任何线索。

I don't know which BSONElement has the wrong type. And I've already googled the assertionCode: 13111. I've also checked in the MongoDB log, but did not find any clues there.

有没有人有想法，我可能会遗漏/做错什么？如果你们需要更多详细信息，请告诉我们。

Does anyone have an idea, what I could be missing/doing wrong? If you guys need more details, just let me know please.

推荐答案

今天我偶然发现了我的错误并计划分享解决方案这里，以防有人遇到类似的问题。

Today I stumbled upon my mistake and figured to share the solution here, just in case somebody encounters a similar problem.

调用 mapReduce 方法导致了问题：

The invocation of the mapReduce method was causing the problem:

MapReduceOutput sum = collection
                .mapReduce(MAP, REDUCE_MAX, null, null);

查看此方法的Javadoc：

Have a look at the Javadoc for this method:

/**
 * performs a map reduce operation
 * Runs the command in REPLACE output mode (saves to named collection)
 *
 * @param map
 *            map function in javascript code
 * @param outputTarget
 *            optional - leave null if want to use temp collection
 * @param reduce
 *            reduce function in javascript code
 * @param query
 *            to match
 * @return
 * @throws MongoException
 * @dochub mapreduce
 */

它声明该命令是使用 REPLACE 作为输出模式，如果想要临时收集， outputTarget 应为 null 。

It states that the command is executed using REPLACE as output mode and that if one wants a temporary collection, the outputTarget should be null.

不幸的是，构造函数 MapReduceCommand ，用于 mapReduce 方法，只允许 outputTar如果 OutputType 设置为 INLINE ，则可以为空（根据Javadoc的 MapReduceCommand.getOutputTarget（））。

Unfortunately though, the constructorMapReduceCommand, which is used in the mapReduce method, only allows the outputTarget to be nullable if the OutputType is set to INLINE (according to the Javadoc of MapReduceCommand.getOutputTarget()).

所以我所要做的就是从<$更改第三个参数c $ c> null 到某些 String ，如下所示：

So all I had to do is to change the third parameter from null to some String, like so:

MapReduceOutput sum = collection
                .mapReduce(MAP, REDUCE_MAX, "tmp", null);

这就像我试图找出它为什么没有玩的唯一参数工作。我希望有人可能会觉得这很有用。

This was like the only parameter I had not played around with while trying to figure out why it didn't work. I hope somebody might find this helpful.

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