问题描述
我想获取所有用户 user_totaldocs 和 user_totalthings ，并希望总和变量。
I want to fetch all users user_totaldocs and user_totalthings and want to sum those variables.
怎么可能？这是用户架构：
How can it's possible? Here is user schema:
var user_schema = mongoose.Schema({
local : {
...
...
user_id : String,
user_totaldocs : Number,
user_totalthings : Number
....
}
});
推荐答案
您可以使用将计算字段添加到结果中。下面有一些例子，使用 mongo shell，但是在Mongoose的是相似的。
You can use the Aggregation Pipeline to add calculated fields to a result. There are some examples below using the mongo shell, but the syntax in Mongoose's Aggregate() helper is similar.
例如，要计算总和（每个用户文档），您可以使用 ：
For example, to calculate sums (per user document) you can use the $add expression in a $project stage:
db.user.aggregate(
// Limit to relevant documents and potentially take advantage of an index
{ $match: {
user_id: "foo"
}},
{ $project: {
user_id: 1,
total: { $add: ["$user_totaldocs", "$user_totalthings"] }
}}
)
要计算多个文档的总计数，您需要使用 $ group stage 使用，例如：
To calculate totals across multiple documents you need to use a $group stage with a $sum accumulator, for example:
db.user.aggregate(
{ $group: {
_id: null,
total: { $sum: { $add: ["$user_totaldocs", "$user_totalthings"] } },
totaldocs: { $sum: "$user_totaldocs" },
totalthings: { $sum: "$user_totalthings" }
}}
)
您可能只需要一个总计字段;我已经在 totaldocs 和 totalthings 中添加了计算多个字段的示例。
You may want only the one total field; I've added in totaldocs and totalthings as examples of calculating multiple fields.
_id null 将组合所有传递给<$ c $的文档的值c> $ group stage，但您也可以在此使用其他条件（例如按 user_id 分组）。
A group _id of null will combine values from all documents passed to the $group stage, but you can also use other criteria here (such as grouping by user_id).
这篇关于查询和总和全部与猫鼬的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！