Question

我在 EmployeeDB 中有三个集合。

员工

{ 
    "user_id" : "EMP001", 
    "FirstName" : "Manoj", 
    "LastName" : "sharma", 
    "Status" : "0/1", 
    "CreateDate" : "1988-10-11T18:30:00.000Z"
}

EmpContact

{ 
    "user_id" : "EMP001", 
    "Phone" : "9999999999", 
    "Email" : "xyz@gmail.com"
}

员工信息

{ 
    "user_id" : "EMP001", 
    "Gender" : "Male", 
    "Age" : NumberInt(20), 
    "Designation" : "manager", 
    "Salary" : "5000"
}

我需要将三个集合分组并显示所有字段。我试过下面的代码，

db.Employee.aggregate([
        {$lookup: {from: "EmpContact",localField: "user_id",foreignField: "user_id",as: "contact"}},
        {$unwind:"$EmpContact"},
        {$lookup: {from: "EmpInfo",localField: "user_id",foreignField: "user_id",as: "empinfo"}},
        {$unwind:"$EmpInfo"},
        {
            $match:{user_id : "EMP001"}
        }
]).toArray();

但是我得到了一个空数组，请帮帮我...

Answer 1

问题来自您的 $unwind。由于您在 contact 中将字段命名为 $lookup，因此字段 EmpContact 不存在。第二个 unwind 的情况相同，EmpInfo 不存在但 empinfo 存在

这是完整的查询

db.Employee.aggregate([
  {
    $lookup: {
      from: "EmpContact",
      localField: "user_id",
      foreignField: "user_id",
      as: "contact"
    }
  },
  {
    $unwind: "$contact"
  },
  {
    $lookup: {
      from: "EmpContact",
      localField: "user_id",
      foreignField: "user_id",
      as: "empinfo"
    }
  },
  {
    $unwind: "$empinfo"
  },
  {
    $match: {
      user_id: "EMP001"
    }
  }
])

试试here

聚合查询返回空数组

1 个答案: