$lookup with nested data in mongodb - mongodb

Question

How do I combine 2 array objects using mongoDB NoSQL? Because I have tried to find some of the same problems here that I got, but I have not found the answers and problems that match what I got.
If someone here wants to help me, here are the problems I want to solve.
Example: I tried using noSQL in mongoDB like this:
db.tables.aggregate([
{ $lookup: { from: 'reservations', localField: '_id', foreignField: 'tableId', as: 'reservation' }},
{ $unwind: { path: '$reservation', 'preserveNullAndEmptyArrays': true }},
{ $lookup: { from: 'orders', localField: 'reservation._id', foreignField: 'reservationId', as: 'orders' }},
{ $lookup: { from: 'products', localField: 'orders.productId', foreignField: '_id', as: 'products' }},
{
$project: {
'_id': 1,
'initial': 1,
'description': 1,
'reservation._id': 1,
'reservation.guest': 1,
'orders._id': 1,
'orders.status': 1,
'orders.quantity': 1,
'orders.productId': 1,
'products._id': 1,
'products.name': 1
}
},
]);
After running noSQL mongoDB above, I got the results below:
{
"_id" : ObjectId("5b63e519514cf01c2864749a"),
"description" : "Kursi VIP 01",
"reservation" : {
"_id" : ObjectId("5b63f104514cf01c286474b6"),
"guest" : "Jhon Doe"
},
"orders" : [
{
"_id" : ObjectId("5b63f239514cf01c286474bb"),
"productId" : ObjectId("5b63e72d514cf01c286474a3"),
"status" : "3",
"quantity" : "2"
},
{
"_id" : ObjectId("5b63f252514cf01c286474bc"),
"productId" : ObjectId("5b63e7de514cf01c286474a6"),
"status" : "2",
"quantity" : "3"
},
{
"_id" : ObjectId("5b63f267514cf01c286474bd"),
"productId" : ObjectId("5b63e937514cf01c286474ac"),
"status" : "0",
"quantity" : "2"
}
],
"products" : [
{
"_id" : ObjectId("5b63e72d514cf01c286474a3"),
"name" : "AQUA 600ML"
},
{
"_id" : ObjectId("5b63e7de514cf01c286474a6"),
"name" : "Nasi Goreng Kecap Asin"
},
{
"_id" : ObjectId("5b63e937514cf01c286474ac"),
"name" : "Daging Ayam Goreng"
}
]
}
Now, my Question is. How to merge/combine 2 Object Array ("orders and products"), So I can get results like this:
{
"_id" : ObjectId("5b63e519514cf01c2864749a"),
"description" : "Kursi VIP 01",
"reservation" : {
"_id" : ObjectId("5b63f104514cf01c286474b6"),
"guest" : "Jhon Doe"
},
"orders" : [
{
"_id" : ObjectId("5b63f239514cf01c286474bb"),
"productId" : ObjectId("5b63e72d514cf01c286474a3"),
"name" : "AQUA 600ML",
"status" : "3",
"quantity" : "2"
},
{
"_id" : ObjectId("5b63f252514cf01c286474bc"),
"productId" : ObjectId("5b63e7de514cf01c286474a6"),
"name" : "Nasi Goreng Kecap Asin",
"status" : "2",
"quantity" : "3"
},
{
"_id" : ObjectId("5b63f267514cf01c286474bd"),
"productId" : ObjectId("5b63e937514cf01c286474ac"),
"name" : "Daging Ayam Goreng"
"status" : "0",
"quantity" : "2"
}
]
}
I hope, someone can help me.
Thanks in advance.

Answer 1

You can try below aggregation with mongodb 3.4
You need to $unwind the orders array to add the field($addFields) name inside orders and then $group to rollback orders again to the make an array field
db.tables.aggregate([
{ "$lookup": {
"from": "reservations",
"localField": "_id",
"foreignField": "tableId",
"as": "reservation"
}},
{ "$unwind": { "path": '$reservation', 'preserveNullAndEmptyArrays': true }},
{ "$lookup": {
"from": "orders",
"localField": "reservation._id",
"foreignField": "reservationId",
"as": "orders",
}},
{ "$unwind": { "path": '$orders', 'preserveNullAndEmptyArrays': true }},
{ "$lookup": {
"from": "products",
"localField": "orders.productId",
"foreignField": "_id",
"as": "orders.products"
}},
{ "$unwind": { "path": '$orders.products', 'preserveNullAndEmptyArrays': true }},
{ "$addFields": {
"orders.name": "$orders.products.name"
}},
{ "$group": {
"_id": "$_id",
"description": { "$first": "$description" },
"reservation": { "$first": "$reservation" },
"orders": { "$push": "$orders" }
}},
{ "$project": { "orders.products": 0 }}
])
Which is far simple with mongodb 3.6 nested $lookup version
db.tables.aggregate([
{ "$lookup": {
"from": "reservations",
"let": { "reservationId": "$_id" },
"pipeline": [
{ "$match": { "$expr": { "$eq": [ "$tableId", "$$reservationId" ] } } }
],
"as": "reservations"
}},
{ "$lookup": {
"from": "orders",
"let": { "reservationId": "$reservation._id" },
"pipeline": [
{ "$match": { "$expr": { "$eq": [ "$reservationId", "$$reservationId" ] } } },
{ "$lookup": {
"from": "products",
"let": { "productId": "$productId" },
"pipeline": [
{ "$match": { "$expr": { "$eq": [ "$_id", "$$productId" ] } } },
{ "$project": { "_id": false }}
],
"as": "products"
}},
{ "$unwind": "$products" },
{ "$addFields": { "name": "$products.name" } },
{ "$project": { "products": 0 }}
],
"as": "orders"
}}
])