Mongoose的小组(By)？

Question

我在shell中构造了我想要的查询但是在Mongoose中编写它时遇到了麻烦.

db.commentstreams.group({ key: { page_id: true }, reduce: function(obj,prev) { prev.num_comments += obj.num_comments }, initial: { num_comments: 0 } })

我对Mongoose语法感到有点困惑; 也许有人可以对这一点有所了解.非常感谢.

Answer 1

根据这篇文章:

Model.find({}, [fields], {'group': 'FIELD'}, function(err, logs) { 
        ... 
}); 

不幸的是,我们似乎缺乏这方面的文档.

Answer 2

MapReduce应该是正确的方法,但是如果你没有分片,你的查询不会导致超过10k的记录就可以了.

您可以通过moongoose访问任何node-mongodb-native函数,所以它看起来像这样:

var group = {
   key: {},
   cond: {item_id: item_id},
   reduce: function(doc, out) {
      out.count++;
      out.total += doc.value;
   },
   initial: {
       total: 0,
       count: 0
   },
   finalize: function(out) {
       out.avg = out.total / out.count;
   }
};

Item.collection.group(group.key, group.cond, group.initial, group.reduce, group.finalize, true, function(err, results) {
    console.log('group results %j', results);
});

node-mongodb-native source:https: //github.com/mongodb/node-mongodb-native/blob/master/lib/mongodb/collection.js#L1165

MongoDB小组doc:http: //www.mongodb.org/display/DOCS/Aggregation#Aggregation-Group