Unwind children array of objects - mongodb

Question

I have an array of objects in a collection. I show two documents to show the structure of these array.
The property "tipos" is an array of objects. And inside this child array, the property "ingredientes" is another array of objects.
{
"_id" : ObjectId("5c6c32337acdd946b66f76e9"),
"name" : "Ensaladas",
"tipos" : [
{
"name" : "Rusa",
},
{
"name" : "Cesars",
"ingredientes" : [
{
"name" : "Lechuga",
"amount" : 20
},
{
"name" : "Vinagreta",
"amount" : 10
}
]
},
{
"name" : "Campesina",
"ingredientes" : [
{
"name" : "Beterraga",
"amount" : 55
}
]
}
]
},
{
"_id" : ObjectId("5c6c32337acdd946b66f76e9"),
"name" : "Carnes",
"tipos" : [
{
"name" : "Estofado de pollo",
},
{
"name" : "Lomo saltado",
"ingredientes" : [
{
"name" : "Lomo fino",
"amount" : 50
},
{
"name" : "Tomate",
"amount" : 15
}
]
}
]
}
I need to unwind it enough to get this result:
Ensaladas Rusa
Ensaladas Cesars Lechuga
Ensaladas Cesars Vinagreta
Ensaladas Campesina Beterraga
Carnes Estofado de pollo
Carnes Lomo saltado Lomo fino
Carnes Lomo saltado Tomate
I have been trying double unwind but not getting the result I need.
Thanks.

Answer 1

You need to use $unwind with preserveNullAndEmptyArrays set to true since not all the documents contain tipos.ingredientes path. Then you can use $concat with $rtrim to build the name as single string, try:
db.col.aggregate([
{ $unwind: "$tipos" },
{ $unwind: { path: "$tipos.ingredientes", preserveNullAndEmptyArrays: true } },
{ $project: { _id: 0, name: { $rtrim: { input: { $concat: [ "$name", " ", "$tipos.name", " ", { $ifNull: [ "$tipos.ingredientes.name", "" ] } ] } } } } }
])
Outputs:
{ "name" : "Ensaladas Rusa" }
{ "name" : "Ensaladas Cesars Lechuga" }
{ "name" : "Ensaladas Cesars Vinagreta" }
{ "name" : "Ensaladas Campesina Beterraga" }
{ "name" : "Carnes Estofado de pollo" }
{ "name" : "Carnes Lomo saltado Lomo fino" }
{ "name" : "Carnes Lomo saltado Tomate" }