How can I get the lowest values in a MongoDB collection? - mongodb

Question

I have a MongoDB collection called product which has the following documents as seen below.
{
"product" : "Milk",
"barcode" : 12345,
"price" : 100,
"store" : "BestBuy"
},
{
"product" : "Milk",
"barcode" : 12345,
"price" : 100,
"store" : "WalMart"
},
{
"product" : "Milk",
"barcode" : 12345,
"price" : 130,
"store" : "Target"
},
{
"product" : "Milk",
"barcode" : 12345,
"price" : 500,
"store" : "Game"
}
I wish to query the collection and only return documents that have the lowest price e.g
{
product: "Milk",
barcode: 12345,
price: 100,
store: "BestBuy"
}
{
product: "Milk",
barcode: 12345,
price: 100,
store: "WalMart"
}
But when I run my aggregation query:
db.test.aggregate([{$match:{barcode:1234}},{$group: {_id:"$name", price: {$min:"$price"} } }])
It only returns one document.

Answer 1

You need to $group your documents by "price". From there, you $sort them by "_id" in ascending order and use $limit to return the first document which nothing other than the document with the minimum value.
db.products.aggregate([
{ "$group": {
"_id": "$price",
"docs": { "$push": "$$ROOT" }
}},
{ "$sort": { "_id": 1 } },
{ "$limit": 1 }
])
which produces something like:
{
"_id" : 100,
"docs" : [
{
"_id" : ObjectId("574a161b17569e552e35edb5"),
"product" : "Milk",
"barcode" : 12345,
"price" : 100,
"store" : "BestBuy"
},
{
"_id" : ObjectId("574a161b17569e552e35edb6"),
"product" : "Milk",
"barcode" : 12345,
"price" : 100,
"store" : "WalMart"
}
]
}