有没有一种方法可以对Mongo数据进行分组，或者我需要在node/javascript中进行分组

我有一个mongo集合。使用node.js驱动程序：
db.collection（'notify'）.find（）
退货：

{ _id: '1376179201714-user102',  
  state: 'unread',  
  sender: 'Daily Notify Process',  
  datereceived: 1376179201714,  
  subject: 'Training is past due!',  
  message: 'Training3 is past due!!!',  
  recipient: [ 'test@test.com' ] }  
{ _id: '1376179201714-user103',  
  state: 'unread',  
  sender: 'Daily Notify Process',  
  datereceived: 1376179201714,  
  subject: 'training is past due!',  
  message: 'Training2 is past due!!!',  
  recipient: [ 'test@test.com' ] }  
{ _id: '1376179201714-user104',  
  state: 'unread',  
  sender: 'Daily Notify Process',  
  datereceived: 1376179201714,  
  subject: 'training is past due!',  
  message: 'Training5 is past due!!!',  
  recipient: [ 'test@test.com' ] }  
{ _id: '1376179201714-user133',  
  state: 'unread',  
  sender: 'Daily Notify Process',  
  datereceived: 1376179201714,  
  subject: 'training is past due!',  
  message: 'Training1 is past due!!!',  
  recipient: [ 'test2@test.com' ] }  
{ _id: '1376179201714-user134',  
  state: 'unread',  
  sender: 'Daily Notify Process',  
  datereceived: 1376179201714,  
  subject: 'training is past due!',  
  message: 'Training2 is past due!!!',  
  recipient: [ 'test2@test.com' ] }  
{ _id: '1376179201714-user135',  
  state: 'unread',  
  sender: 'Daily Notify Process',  
  datereceived: 1376179201714,  
  subject: 'training is past due!',  
  message: 'Training4 is past due!!!',  
  recipient: [ 'test2@test.com' ] }      
{ _id: '1376179201714-user203',  
  state: 'unread',  
  sender: 'Daily Notify Process',  
  datereceived: 1376179201714,  
  subject: 'training is past due!',  
  message: 'Training1 is past due!!!',  
  recipient: [ 'test3@test.com' ] }  
{ _id: '1376179201714-user204',  
  state: 'unread',  
  sender: 'Daily Notify Process',  
  datereceived: 1376179201714,  
  subject: 'Training2 is past due!', 
  message: 'Card maker, updating member info is past due!!!',  
  recipient: [ 'test3@test.com' ] }  
{ _id: '1376179201714-user205',  
  state: 'unread',  
  sender: 'Daily Notify Process',  
  datereceived: 1376179201714,  
  subject: 'training is past due!',  
  message: 'Training3 is past due!!!',  
  recipient: [ 'test3@test.com' ] }

我可以用mapreduce或group:把它变成这样吗

{recipient: ['test@test.com'],  
subject: 'Training is past due!',  
trainingblock: [  
    {message: 'Training3 is past due!!!'},  
    {message: 'Training2 is past due!!!'},   
    {message: 'Training5 is past due!!!'}  
    ]  
}  
{recipient: ['test@test.com'],  
subject: 'Training is past due!',  
trainingblock: [  
    {message: 'Training1 is past due!!!'},  
    {message: 'Training2 is past due!!!'},   
    {message: 'Training4 is past due!!!'}  
    ]  
}  
{recipient: ['test@test.com'],  
subject: 'Training is past due!',  
trainingblock: [  
    {message: 'Training1 is past due!!!'},  
    {message: 'Training2 is past due!!!'},  
    {message: 'Training3 is past due!!!'}  
    ]  
}

还是我需要在javascript/节点端执行此操作？

这是我在没有花费大量时间的情况下得到的最接近的结果。我不知道所有的要求，也不知道你的数据有多大变化。例如，即使接收者被封装在数组中，它也总是一个值吗？无论如何，它应该足够近，让你走完剩下的路。

它是按照收件人和主题进行分组，然后一起发送消息。reduce函数创建容器，并为传入的每个消息将值推入trainingblock。

db.collection.mapReduce(function() {
  var recipient = this.recipient[0];
  emit(recipient + "#" + this.subject, { message: this.message });
}, function(key, values) {
  var parts = key.split('#'),
      recipient = parts[0],
      subject = parts[1],
      block = { recipient: recipient, subject: subject, trainingblock: [] };
    for(var i = 0; i < values.length; i++) {
      block.trainingblock.push({ message: values[i].message });
    }
    return block;
}, {out: { inline: 1 }});

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