Get info from another collection based of _id and merge - MongoDB - node.js

Question

I have two collections. Lets call one baskets and the other one fruits.
In baskets we have the following document:
[{
basket_name: "John's Basket",
items_in_basket: [
{
fruit_id: 1,
comment: "Delicious!"
},
{
fruit_id: 2,
comment: "I did not like this"
}
]
}]
And in fruits we have the following documents:
[{
_id: 1,
fruit_name: "Strawberry",
color: "Red"
},
{
_id: 2,
fruit_name: "Watermelon",
color: "Green"
}]
How do I get information on each fruit in John's Basket?
The result should look like this:
[{
fruit_id: 1,
comment: "Delicious!",
fruit_name: "Strawberry",
color: "Red"
},
{
fruit_id: 2,
comment: "I did not like this",
fruit_name: "Watermelon",
color: "Green"
}]

Answer 1

There's no "join" in MongoDB. You either could:
consider using a MapReduce function to create a new structure that contains the merged data
write the code necessary to fetch each fruit instance on demand and merge it in your client code with a basket document.
denormalize the data and include the details for each fruit in the basket document. This poses it's own set of issues as data is duplicated and updates to a particular fruit would then need to be made to every usage in the collection.
Both have their pros and cons.
You might find this Q/A helpful, and also this documentation for MongoDB.

Answer 2

this is no longer true.
Since version 3.2, MongoDB added the $lookup command.
https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/
db.orders.insert([
{ "_id" : 1, "item" : "almonds", "price" : 12, "quantity" : 2 },
{ "_id" : 2, "item" : "pecans", "price" : 20, "quantity" : 1 },
{ "_id" : 3 }
])
db.inventory.insert([
{ "_id" : 1, "sku" : "almonds", description: "product 1", "instock" : 120 },
{ "_id" : 2, "sku" : "bread", description: "product 2", "instock" : 80 },
{ "_id" : 3, "sku" : "cashews", description: "product 3", "instock" : 60 },
{ "_id" : 4, "sku" : "pecans", description: "product 4", "instock" : 70 },
{ "_id" : 5, "sku" : null, description: "Incomplete" },
{ "_id" : 6 }
])
db.orders.aggregate([
{
$lookup:
{
from: "inventory",
localField: "item",
foreignField: "sku",
as: "inventory_docs"
}
}
])
returns:
{
"_id" : 1,
"item" : "almonds",
"price" : 12,
"quantity" : 2,
"inventory_docs" : [
{ "_id" : 1, "sku" : "almonds", "description" : "product 1", "instock" : 120 }
]
}
{
"_id" : 2,
"item" : "pecans",
"price" : 20,
"quantity" : 1,
"inventory_docs" : [
{ "_id" : 4, "sku" : "pecans", "description" : "product 4", "instock" : 70 }
]
}
{
"_id" : 3,
"inventory_docs" : [
{ "_id" : 5, "sku" : null, "description" : "Incomplete" },
{ "_id" : 6 }
]
}