环回上的MongoDB聚合

本文介绍了环回上的MongoDB聚合的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 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 github/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); }); });