How to get data from two collection in NO SQL Database MongoDB

#mongodb #node #webdev #database

Like I have two collection first is Employee collection and second is Department collection.

Employee collection having below data:

{
  "_id": "kcXtyaB7jGPw9Ks",
  "name": "Test name",
  "post": "Manager",
  "departmentId": "xQQrzRgi8",
  "dateCreated": "2022-07-12T13:09:16.270Z",
  "dateModified": "2022-07-12T13:09:16.270Z"
},
{
  "_id": "mNkyaB6jGPw7KB",
  "name": "Test2 name",
  "post": "Manager",
  "departmentId": "56sgAeKfx",
  "dateCreated": "2022-07-12T13:09:16.270Z",
  "dateModified": "2022-07-12T13:09:16.270Z"
}

Department collection having data like below:

    {
      "_id": "xQQrzRgi8",
      "departmentName": "Testing department"
    },
    {
      "_id": "56sgAeKfx",
      "departmentName": "HR department"
    }

In response of Employee data we want department name with departmentId like below we want response:

{
    "_id": "kcXtyaB7jGPw9Ks",
    "dateCreated": "2022-07-12T13:09:16.270Z",
    "dateModified": "2022-07-12T13:09:16.270Z",
    "departmentId": "xQQrzRgi8",
    "departmentName": "Testing department",
    "name": "Test name",
    "post": "Manager"
  },
  {
    "_id": "mNkyaB6jGPw7KB",
    "dateCreated": "2022-07-12T13:09:16.270Z",
    "dateModified": "2022-07-12T13:09:16.270Z",
    "departmentId": "56sgAeKfx",
    "departmentName": "HR department",
    "name": "Test2 name",
    "post": "Manager"
  }

For above solution we have to aggregate in MongoDB like below:

Here is Example with Query: https://mongoplayground.net/p/V-SC5pmKQR7

db.Employee.aggregate([
  {
    $lookup: {
      from: "Department",
      localField: "departmentId",
      foreignField: "_id",
      as: "departmentName",
    },
  },
  {
    $set: {
      departmentName: {
        $first: "$departmentName.departmentName"
      },   
    }, 
  }
])

In response of employee data want department name only Instead departmentId Then Query will be like below:

db.Employee.aggregate([
  {
    $lookup: {
      from: "Department",
      localField: "departmentId",
      foreignField: "_id",
      as: "departmentName",
    },
  },
  {
    $set: {
      departmentName: {
        $first: "$departmentName.departmentName"
      },
    },
  },
  {
    $project: {
      departmentId: 0
    },
  },
])

HERE is Query with example: https://mongoplayground.net/p/M4Nn7ud33KL

Happy coding!!!