Find Documents

# find_one() — retrieve a single document from the Dataplexa Store

from pymongo import MongoClient

client = MongoClient("mongodb://localhost:27017/")
db     = client["dataplexa"]

# Fetch user Alice by her _id
alice = db.users.find_one({"_id": "u001"})
print("User:", alice["name"], "—", alice["city"], alice["country"])

# Fetch the first product in the Electronics category
first_electronic = db.users.find_one({"membership": "premium"})
print("First premium user:", first_electronic["name"])

# find_one() returns None when no match exists
missing = db.users.find_one({"_id": "u999"})
print("Missing user:", missing)

# Always guard against None before accessing fields
user = db.users.find_one({"_id": "u003"})
if user:
    print("Found:", user["name"])
else:
    print("No user found")

# find() — retrieve multiple documents as a cursor

from pymongo import MongoClient

client = MongoClient("mongodb://localhost:27017/")
db     = client["dataplexa"]

# Fetch all users — empty filter matches every document
all_users = db.users.find({})

print("All users:")
for user in all_users:
    print(f"  {user['_id']} — {user['name']} ({user['country']})")

# Fetch all premium users
print("\nPremium users:")
premium = db.users.find({"membership": "premium"})
for user in premium:
    print(f"  {user['name']}")

# Convert cursor to a list — loads all results into memory
products_list = list(db.products.find({}))
print(f"\nTotal products in memory: {len(products_list)}")

# Projections — include or exclude specific fields

from pymongo import MongoClient

client = MongoClient("mongodb://localhost:27017/")
db     = client["dataplexa"]

# ── INCLUSION projection — specify fields to return ──────
# 1 = include, _id is included by default unless excluded
print("Inclusion projection — name and email only:")
users = db.users.find({}, {"name": 1, "email": 1})
for u in users:
    print(f"  {u}")

# ── EXCLUSION projection — specify fields to hide ────────
# 0 = exclude
print("\nExclusion projection — hide tags and joined:")
users = db.users.find({}, {"tags": 0, "joined": 0})
for u in users:
    print(f"  {u}")

# ── Exclude _id from an inclusion projection ─────────────
print("\nInclusion without _id:")
products = db.products.find(
    {"category": "Electronics"},
    {"name": 1, "price": 1, "_id": 0}   # _id: 0 explicitly excluded
)
for p in products:
    print(f"  {p}")

# Sorting — order results by one or more fields

from pymongo import MongoClient, ASCENDING, DESCENDING

client = MongoClient("mongodb://localhost:27017/")
db     = client["dataplexa"]

# Sort products by price ascending (cheapest first)
print("Products cheapest first:")
cheap_first = db.products.find({}, {"name": 1, "price": 1, "_id": 0}).sort("price", ASCENDING)
for p in cheap_first:
    print(f"  ${p['price']:>7.2f}  {p['name']}")

# Sort products by price descending (most expensive first)
print("\nProducts most expensive first:")
expensive_first = db.products.find({}, {"name": 1, "price": 1, "_id": 0}).sort("price", DESCENDING)
for p in expensive_first:
    print(f"  ${p['price']:>7.2f}  {p['name']}")

# Multi-field sort — category ascending, then price descending within each category
print("\nBy category A-Z, then price high to low:")
multi_sort = db.products.find(
    {}, {"name": 1, "category": 1, "price": 1, "_id": 0}
).sort([("category", ASCENDING), ("price", DESCENDING)])
for p in multi_sort:
    print(f"  {p['category']:12} ${p['price']:>7.2f}  {p['name']}")

# limit() and skip() — pagination

from pymongo import MongoClient, ASCENDING

client = MongoClient("mongodb://localhost:27017/")
db     = client["dataplexa"]

page_size = 3

# Page 1 — first 3 products sorted by price
page_1 = db.products.find(
    {}, {"name": 1, "price": 1, "_id": 0}
).sort("price", ASCENDING).limit(page_size).skip(0)

print("Page 1 (products 1–3):")
for p in page_1:
    print(f"  ${p['price']:>7.2f}  {p['name']}")

# Page 2 — next 3 products
page_2 = db.products.find(
    {}, {"name": 1, "price": 1, "_id": 0}
).sort("price", ASCENDING).limit(page_size).skip(page_size)

print("\nPage 2 (products 4–6):")
for p in page_2:
    print(f"  ${p['price']:>7.2f}  {p['name']}")

# Pagination helper function
def get_page(collection, filter_query, sort_field, page_num, page_size=3):
    skip_count = (page_num - 1) * page_size
    return list(
        collection.find(filter_query)
        .sort(sort_field, ASCENDING)
        .skip(skip_count)
        .limit(page_size)
    )

page = get_page(db.products, {}, "price", page_num=1)
print(f"\nPagination helper — page 1: {len(page)} products")

# count_documents() — counting results

from pymongo import MongoClient

client = MongoClient("mongodb://localhost:27017/")
db     = client["dataplexa"]

# Total documents per collection
print("Collection counts:")
print("  users:   ", db.users.count_documents({}))
print("  products:", db.products.count_documents({}))
print("  orders:  ", db.orders.count_documents({}))
print("  reviews: ", db.reviews.count_documents({}))

# Count with a filter
premium_count   = db.users.count_documents({"membership": "premium"})
delivered_count = db.orders.count_documents({"status": "delivered"})
expensive_count = db.products.count_documents({"price": {"$gt": 100}})

print(f"\nPremium users:       {premium_count}")
print(f"Delivered orders:    {delivered_count}")
print(f"Products over $100:  {expensive_count}")