MongoDB 中的 db.eval() 错误

Question

我正在尝试运行使用 db.eval() 方法的 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.execute(DBPort.java:164)
at com.mongodb.DBPort.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 工作的正确方法是通过 mapReduce command which is exposed in the Java driver via the MapReduceCommand helper。

eval command 并非用于此目的（并且在 MongoDB 3.0 中也已弃用）。

MongoDB 中的 db.eval() 错误

Error in db.eval() in MongoDB

java

mapreduce

mongodb

mongo-java