Countries of birth by prize category

Some prize categories have laureates hailing from a greater number of countries than do other categories. You will build an aggregation pipeline for the prizes collection to collect these numbers, using a $lookup stage to obtain laureate countries of birth.

Este exercício faz parte do curso

Introduction to MongoDB in Python

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Instruções do exercício

$unwind the laureates array field to output one pipeline document for each array element.
After pulling in laureate bios with a $lookup stage, unwind the new laureate_bios array field (each laureate has only a single biography document).
Collect the set of bornCountries associated with each prize category.
Project out the size of each category's set of bornCountries.

Exercício interativo prático

Experimente este exercício completando este código de exemplo.

pipeline = [
    # Unwind the laureates array
    {____: "$laureates"},
    {"$lookup": {
        "from": "laureates", "foreignField": "id",
        "localField": "laureates.id", "as": "laureate_bios"}},

    # Unwind the new laureate_bios array
    {"$unwind": ____},
    {"$project": {"category": 1,
                  "bornCountry": "$laureate_bios.bornCountry"}},

    # Collect bornCountry values associated with each prize category
    {"$group": {____: "$category",
                "bornCountries": {"$addToSet": "$bornCountry"}}},

    # Project out the size of each category's (set of) bornCountries
    {"$project": {"category": 1,
                  "nBornCountries": {"$size": ____}}},
    {"$sort": {"nBornCountries": -1}},
]
for doc in db.prizes.aggregate(pipeline): print(doc)

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