Mongoose返回数组$ size(Mongoose return array $size)

Mongoose返回数组$ size(Mongoose return array $size)

我有一份文件：

{ _id: 98556a665626a95a655a, first_name: 'Panda', last_name: 'Panda, notifications: [{ _id: '', // ... }] }

我想返回以下回复：

{ _id: 98556a665626a95a655a, first_name: 'Panda', last_name: 'Panda', notifications: 2 }

问题是关于通知计数字段，

我使用了Mongoose NodeJS包，我尝试了以下方法：

UserDBModel.findOne({_id: uid}, {notifications: {$size: '$notifications'}}, function(err, user){ });

但似乎行不通。 有人可以帮帮我吗？ :)

提前致谢。

I have a document :

{ _id: 98556a665626a95a655a, first_name: 'Panda', last_name: 'Panda, notifications: [{ _id: '', // ... }] }

I want to return the following response :

{ _id: 98556a665626a95a655a, first_name: 'Panda', last_name: 'Panda', notifications: 2 }

The problem is about notifications count field,

I used Mongoose NodeJS package and I tried the following :

UserDBModel.findOne({_id: uid}, {notifications: {$size: '$notifications'}}, function(err, user){ });

But it seems to not work. Someone can help me ? :)

Thanks in advance.

最满意答案

将aggregate与project管道运算符一起使用。

UserDBModel.aggregate() .match({_id: uid}) .project({ first_name: 1, last_name: 1, notifications: {$size:"$notifications"} }) .exec(function(err, notifications) { // notifications will be an array, you probably want notifications[0] });

请注意，您必须明确指定项目操作员的字段。

Use aggregate with a project pipeline operator.

UserDBModel.aggregate() .match({_id: uid}) .project({ first_name: 1, last_name: 1, notifications: {$size:"$notifications"} }) .exec(function(err, notifications) { // notifications will be an array, you probably want notifications[0] });

Note that you will have to explicitly specify the fields for the project operator.