java - MongoDB 中的 db.eval() 错误

Question

我正在尝试使用db.eval()方法运行map-reduce脚本。

    MongoClient mongo = new MongoClient("localhost", 27017);
    DB mongodb = (DB) mongo.getDB("testDB");

    String script = "db.collection.mapReduce("
            + "function() {emit(this.class, this.marks);},"
            + "function(key, values) { return {\"sum\":Array.sum(values)};},"
               + "{ "
                   + " query : {_id:{$lt:50}},"
                   + "out:\"collectionMapReduce\""
               + "}"
           + ")";

    Object result = mongodb.eval(script);

我收到以下错误:

Exception in thread "main" com.mongodb.MongoException$Network: Read operation to server localhost:27017 failed on database testDB
at com.mongodb.DBTCPConnector.innerCall(DBTCPConnector.java:298)
at com.mongodb.DBTCPConnector.call(DBTCPConnector.java:269)
at com.mongodb.DBCollectionImpl.find(DBCollectionImpl.java:84)
at com.mongodb.DB.command(DB.java:320)
at com.mongodb.DB.command(DB.java:299)
at com.mongodb.DB.command(DB.java:374)
at com.mongodb.DB.command(DB.java:246)
at com.mongodb.DB.doEval(DB.java:445)
at com.mongodb.DB.eval(DB.java:463)
at com.dev.TestMapReduce.main(TestMapReduce.java:25)

Caused by: java.io.EOFException
at org.bson.io.Bits.readFully(Bits.java:75)
at org.bson.io.Bits.readFully(Bits.java:50)
at org.bson.io.Bits.readFully(Bits.java:37)
at com.mongodb.Response.<init>(Response.java:42)
at com.mongodb.DBPort$1.execute(DBPort.java:164)
at com.mongodb.DBPort$1.execute(DBPort.java:158)
at com.mongodb.DBPort.doOperation(DBPort.java:187)
at com.mongodb.DBPort.call(DBPort.java:158)
at com.mongodb.DBTCPConnector.innerCall(DBTCPConnector.java:290)
... 9 more

我无法理解此错误的原因。我该如何解决这个问题？

Note: I am able to perform this job using db.collection.mapReduce(). But I am just trying to achieve this using db.eval()

Answer 1

运行 Map/Reduce 作业的正确方法是通过 mapReduce command它通过 MapReduceCommand helper 在 Java 驱动程序中公开.

eval command不适用于此目的(并且在 MongoDB 3.0 中也已被弃用)。