Group by调用另一个函数，根据golang mongodb中的Group by元素对文档进行计数

我使用golang作为Mongodb的后端

我的mongodb收藏是

**employee**
{
  _id:ObjectId(),
  "emp_name":"qwert",
  "emp_id":111,
  "emp_dept":"XYZ"
  "qualification":"PHD",
   "employee_status":"working"
}
{
_id:ObjectId(),
  "emp_name":"asdfg",
  "emp_id":121,
  "emp_dept":"XYZ"
 "qualification":"MBA"
 "employee_status":"working"
}
**department**
{
    _id:ObjectId(),
    "dept_id":11,
    "dept_name":"XYZ",
    "description":"decs",
    "department_status":"active"
    }

我的密码是

 type DepartmentInfo struct {
    DepartmentID    int                `json:"dept_id" bson:"dept_id"`
    DepartmentName  string             `json:"dept_name" bson:"dept_name"` 
    Description     string             `json:"description" bson:"description"` 
    EmployeeCount   int                `json:"employee_count" bson:"employee_count"`
}

collection := session.DB("db").C("employee")
pipeline := collection.Pipe([]bson.M{
        {"$match": bson.M{ "qualification": "PHD", }},
        {"$group": bson.M{"_id": "$emp_dept",
                "total_employee": bson.M{"$sum": GetDepartmentEmployeeCount("$emp_dept")},                         }},
        {"$lookup": bson.M{
        "from":         "department",
        "localField":   "_id",
        "foreignField": "dept_name",
        "as":           "department_info",
    }},
     {"$unwind": "$department_info"},
     {"$match": bson.M{"$or": []interface{}{
        bson.M{"department_info.status": bson.M{"$exists": false}},
        bson.M{"department_info.status": 1}, // department 1 means active
    }}},   
    })
var departmentInfo [] Department
err = pipeline.All(&departmentInfo)

其他功能为

func GetDepartmentEmployeeCount(var interface{})(int res)
{
  ......
  return res
}

---

当我在

GetDepartmentEmployeeCount

函数中获得

emp\u dept

时，它会像字符串一样打印它，而不是像

emp\u dept

那样获取值。我想执行类似

select count（*）的查询从employee where emp_dept='var'

。我的问题是如何让另一个函数中的group by元素执行查询？

能否澄清您希望看到的输出？你现在得到了什么？