mongodb mapreduce作用域-ReferenceError [英] mongodb mapreduce scope - ReferenceError

问题描述

我正在尝试在mongodb map/reduce函数中使用外部对象.如果对象具有应访问的变量，则会发生错误.

I'm trying to use an external object inside mongodb map/reduce functions. If the object has a variable which it should access, an error occurs.

例如:

var conn = new Mongo();
var db = conn.getDB("test");

var HelperClass = function() {
  var v = [1, 2, 3];

  this.data = function() {
    return v;
  };
};

var helper = new HelperClass();

var map = function() {
  helper.data().forEach(function(value) {
    emit(value, 1);
  });
};

var reduce = function(key, values) {
  var count = 0;
  values.forEach(function(entry) {
    count += entry;
  });
  return count;
};

db.test.mapReduce(map, reduce, {
  out: "temp",
  scope: {
    helper: helper
  }
});

mongodb的输出:

The output from mongodb:

map reduce失败:{"errmsg":例外:ReferenceError:v不是 已定义，"代码:16722，"确定:0}在 src/mongo/shell/collection.js:970

map reduce failed:{ "errmsg" : "exception: ReferenceError: v is not defined", "code" : 16722, "ok" : 0 } at src/mongo/shell/collection.js:970

这是预期的行为吗?还有其他方法可以在mapReduce中使用外部对象吗?

Is it an expected behavior? Is there any other way to use external objects in mapReduce?

推荐答案

造成此问题的原因是此函数:

What's casuing the problem is this function:

var HelperClass = function() {
  var v = [1, 2, 3];

  this.data = function() {
    return v.data;
  };
};

因为:

return v.data;

与实际变量this.v.data的作用域不同.

Is in a different scope to the real variable which is actually this.v.data.

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