环回上的MongoDB聚合

问题描述

如何获取Loopback PersistedModel的总和?

How do I obtain the sum of a Loopback PersistedModel?

关于如何实现该目标，似乎没有文档.

There does not seem to be a documentation on how to achieve that.

如果可能的话，我希望避免查找所有行并将其汇总到Node.js中.

If possible I would like to avoid having to find all the rows and sum it in Node.js.

从 https://github.com/strongloop/loopback/issues/890中尝试示例

var bookCollection = Book.getDataSource().connector.collection(Book.modelName);

我遇到了错误

throw new Error('MongoDB connection is not established');

如何获取集合的句柄以在MongoDB集合上手动运行聚合查询?

How do I get a handle on the collection to manually run aggregate query on a MongoDB collection?

推荐答案

最终设法使其正常运行.大多数示例都省略了connect()部分.

Finally managed to get it working. Most examples left out the connect() part.

我的工作代码:

Book.getDataSource().connector.connect(function(err, db) {
  var collection = db.collection('Book');
  var author = Book.getDataSource().ObjectID(authorId);
  collection.aggregate([
    { $match: { authorId: author } },
    { $group: {
      _id: authorId,
     total: { $sum: "$price" }
    }}
  ], function(err, data) {
    if (err) return callback(err);
    return callback(null, data);
  });
});

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