使用mongodb中对象字段的值创建新的数组字段(Create new array field with values from object field in mongodb)

 鉴于在我的数据库中，我有这样的对象： 
 
_id: 1,
class: 'x',
urls: {
  'a': '/someAUrl',
  'b': '/someBUrl'
}
 
 我想运行一个脚本，将这些对象转换为： 
 
_id: 1,
class: 'x',
urls: {
  'a': '/someAUrl'
},
urls2: [
  {type:'a', url:'/someAUrl'}
]
 
 必须保留初始URL字段。 我尝试在mongo shell中运行这样的东西但没有成功： 
 
db.eval(db.test.find({ class: 'x' }).snapshot().forEach(   function (e) {     e.urls2 = [{ url: e.urls.a, type: 'a'}];     db.test.save(e);   } ))
 
 有任何想法吗？ 谢谢！ 

Given that in my db I have objects like this:
 
_id: 1,
class: 'x',
urls: {
  'a': '/someAUrl',
  'b': '/someBUrl'
}
 
I would like to run a script that transforms those objects to:
 
_id: 1,
class: 'x',
urls: {
  'a': '/someAUrl'
},
urls2: [
  {type:'a', url:'/someAUrl'}
]
 
The initial urls field must remain. I tried running something like this inside mongo shell with no success:
 
db.eval(db.test.find({ class: 'x' }).snapshot().forEach(   function (e) {     e.urls2 = [{ url: e.urls.a, type: 'a'}];     db.test.save(e);   } ))
 
Any ideas? Thanks!

原文：https://stackoverflow.com/questions/38488037