In this article, we will learn how to join multiple collections with $lookup.
$lookup function allows us to join multiple collections in the same database. the $lookup function (joined collection) will return the sub-array of matched data.
syntax:
$lookup:
{
from: collection to join,
localField: field from the execute query document,
foreignField: field from the join collection document(match with localField),
as:name of the output array
}
from: specifies the collection to perform the join.
localField: specifies the field from the document whose field match to the other collection document
foreignField : specifies the field from the other document
as: specifies the name of the new array to add the result
–first, we need to create two collections:
- schema:
//for employee collection
var employeeSchema = new mongoose.Schema({
name: {
type: String,
},
email: {
type: String,
}
});
//for employeedata collection
var employeeDataSchema = new mongoose.Schema({
empid: {
type: mongoose.Schema.ObjectId,
},
address: {
type: String,
},
phone: {
type: Number,
}
});
const empSchema = mongoose.model('employee', employeeSchema);
const empDataSchema = mongoose.model('employeedata', employeeDataSchema);
- insert data in employee collection:
//insert data in employee collection
exports.addEmp = async (req, res) => {
let data = await new empSchema(req.body).save()
res.status(200).send({
isSuccess: true,
data:data
});
}
output:
- insert data in employeedata collection
exports.add = async (req, res) => {
let result = new empDataSchema(req.body).save()
res.status(200).send({
isSuccess: true,
data:result
});
}
output:
–join employee and employeedata collection using $lookup
exports.empData = async (req, res) => {
const data = await empSchema.aggregate([
{
$lookup:
{
from: "employeedatas",
localField: "_id",
foreignField: "empid",
as: "emp"
}
}
]);
res.status(200).send({
isSuccess: true,
data: data
});
}
output:
