猫鼬找到多个匹配项

Question

我是这项技术的新手，正在使用使用 Mongoose 的 Node 和 Express 服务器。我有以下文档集合架构。

var empSchema = new mongoose.Schema({
 _id: String,
 orgName: {type: String, required: true},
 locName: {type: String, required: true},
 empName: {type: String, required: true}
});

在这里，我在请求中获得了位置名称列表，例如 "NewYork"、"London"、"Paris" 等...，并且需要 return 中的文档回复如下....

{
result:[{locName:"NewYork",
 empList:[
  {orgName:"abc", empName:"emp1"},
  {orgName:"xyz", empName:"emp2"}]
 },
 {locName:"London",
 empList:[
  {orgName:"pkq", empName:"emp13"},
  {orgName:"mns", empName:"emp23"}]
 }]
}

从 Node.js 使用 mongoose 的最佳方式是什么？我认为对 mongodb 进行多次查询（每个查询都有一个位置）是个坏主意。

有没有办法通过单次调用 mongoose 获得预期的 json 响应？谢谢

Answer 1

所有查询，当您需要按称为聚合的总和值进行分组时。您可以在 mongo docs and same methods have model in Mongoose 中阅读相关信息。要生成您的查询，您可以使用如下代码：

Employee
  .aggregate()
  .group({ _id: '$locName', empList: { $push: "$$ROOT" }})
  .exec(function (err, res) {

});

如果不需要全部查询table，还有match方法

Answer 2

是，使用 aggregation framework to get the desired output. The aggregation pipeline will consist of a $group operator pipeline stage which groups the documents by the locName field and the $addToSet accumulator operator to add the orgName and empName fields to an array empList. The last pipeline stage $project 运算符，然后用新字段 locName.

替换先前聚合流中的 _id 字段

为了演示这个概念，假设您有一个示例集合，您使用 mongo shell:

插入

db.employees.insert([
    {
        _id: "1",
        orgName: "abc",
        locName: "New York",
        empName: "emp1"
    },
    {
        _id: "2",
        orgName: "xyz",
        locName: "New York",
        empName: "emp2"
    },
    {
        _id: "3",
        orgName: "pkq",
        locName: "London",
        empName: "emp13"
    },
    {
        _id: "4",
        orgName: "mns",
        locName: "London",
        empName: "emp23"
    }
])

以下聚合生成所需的结果：

db.employees.aggregate([
    {
        "$group": {
            "_id": "$locName",
            "empList": {
                "$addToSet": {
                    "orgName": "$orgName",
                    "empName": "$empName"
                }
            }
        }
    },
    {
        "$project": {
            "_id": 0,
            "locName": "$_id",
            "empList": 1
        }
    }
])

输出:

/* 0 */
{
    "result" : [ 
        {
            "empList" : [ 
                {
                    "orgName" : "mns",
                    "empName" : "emp23"
                }, 
                {
                    "orgName" : "pkq",
                    "empName" : "emp13"
                }
            ],
            "locName" : "London"
        }, 
        {
            "empList" : [ 
                {
                    "orgName" : "xyz",
                    "empName" : "emp2"
                }, 
                {
                    "orgName" : "abc",
                    "empName" : "emp1"
                }
            ],
            "locName" : "New York"
        }
    ],
    "ok" : 1
}

在 Mongoose 中，您可以像这样使用 aggregation pipeline 构建器：

Employee.aggregate()
        .group({
            "_id": "$locName",
            "empList": {
                "$addToSet": {
                    "orgName": "$orgName",
                    "empName": "$empName"
                }
            }
        })
        .project({
            "_id": 0,
            "locName": "$_id",
            "empList": 1
        })
        .exec(function (err, res) {
            if (err) return handleError(err);
            console.log(res); 
    });

// Or the simple aggregate method
var pipeline = [
    {
        "$group": {
            "_id": "$locName",
            "empList": {
                "$addToSet": {
                    "orgName": "$orgName",
                    "empName": "$empName"
                }
            }
        }
    },
    {
        "$project": {
            "_id": 0,
            "locName": "$_id",
            "empList": 1
        }
    }
]

Employee.aggregate(pipeline, function (err, res) {
    if (err) return handleError(err);
    console.log(res); 
});

猫鼬找到多个匹配项

Mongoose find with multiple matches

javascript

mongoose

mongodb

node.js

express