MongoDB Query

Filter and search documents with advanced query conditions

🔍 Advanced Querying

MongoDB queries allow you to filter documents using various conditions. You can search for specific values, ranges, patterns, and complex combinations to find exactly what you need. 


import pymongo

client = pymongo.MongoClient("mongodb://localhost:27017/")
db = client["store"]
products = db["products"]

# Find products over $50
expensive = products.find({"price": {"$gt": 50}})
for product in expensive:
    print(product["name"], product["price"])
$gt
Greater Than
$in
In Array
$regex
Pattern Match

Query Operators

📊

Comparison

Compare values with operators 

# Price greater than 100
products.find({"price": {"$gt": 100}})
📝

Text Search

Search text with patterns 

# Names starting with "A"
users.find({"name": {"$regex": "^A"}})
📋

Array Matching

Find values in arrays 

# Category in list
products.find({"category": {"$in": ["books", "toys"]}})
🔗

Logical Operators

Combine multiple conditions 

# Price between 10 and 50
products.find({"$and": [{"price": {"$gt": 10}}, {"price": {"$lt": 50}}]})

Comparison Operators

Filter documents by comparing field values 

import pymongo

client = pymongo.MongoClient("mongodb://localhost:27017/")
db = client["shop"]
products = db["products"]

# Greater than ($gt)
expensive = products.find({"price": {"$gt": 100}})
print("Expensive products:")
for item in expensive:
    print(f"- {item['name']}: ${item['price']}")

# Less than or equal ($lte)
affordable = products.find({"price": {"$lte": 50}})
print("\nAffordable products:")
for item in affordable:
    print(f"- {item['name']}: ${item['price']}")

# Not equal ($ne)
not_books = products.find({"category": {"$ne": "books"}})
print("\nNon-book items:")
for item in not_books:
    print(f"- {item['name']} ({item['category']})")

Array and List Queries

Search for values within arrays or match against lists 

# Find products in specific categories
categories = ["electronics", "books", "toys"]
filtered = products.find({"category": {"$in": categories}})

print("Products in selected categories:")
for item in filtered:
    print(f"- {item['name']} ({item['category']})")

# Find products NOT in categories
excluded = products.find({"category": {"$nin": ["clothing", "food"]}})

print("\nProducts excluding clothing and food:")
for item in excluded:
    print(f"- {item['name']} ({item['category']})")

Text Pattern Matching

Search text fields using regular expressions 

# Find names starting with "A"
starts_with_a = products.find({"name": {"$regex": "^A"}})
print("Products starting with 'A':")
for item in starts_with_a:
    print(f"- {item['name']}")

# Find names containing "phone" (case insensitive)
phones = products.find({"name": {"$regex": "phone", "$options": "i"}})
print("\nPhone products:")
for item in phones:
    print(f"- {item['name']}")

# Find names ending with "book"
books = products.find({"name": {"$regex": "book$", "$options": "i"}})
print("\nBook products:")
for item in books:
    print(f"- {item['name']}")

Logical Operators

Combine multiple conditions with AND, OR, NOT 

# AND: Both conditions must be true
mid_range = products.find({
    "$and": [
        {"price": {"$gt": 20}},
        {"price": {"$lt": 100}}
    ]
})
print("Mid-range products ($20-$100):")
for item in mid_range:
    print(f"- {item['name']}: ${item['price']}")

# OR: Either condition can be true
cheap_or_books = products.find({
    "$or": [
        {"price": {"$lt": 15}},
        {"category": "books"}
    ]
})
print("\nCheap items or books:")
for item in cheap_or_books:
    print(f"- {item['name']}: ${item['price']} ({item['category']})")

# NOT: Reverse a condition
not_expensive = products.find({
    "$not": {"price": {"$gt": 100}}
})
print("\nNot expensive items:")
for item in not_expensive:
    print(f"- {item['name']}: ${item['price']}")

Practical Query Examples

Real-world query scenarios 

# E-commerce: Find products on sale
def find_sale_items():
    sale_products = products.find({
        "$and": [
            {"on_sale": True},
            {"stock": {"$gt": 0}}
        ]
    })
    
    print("Items on sale (in stock):")
    for item in sale_products:
        print(f"- {item['name']}: ${item['price']} (Stock: {item['stock']})")

# User management: Find active users from specific cities
def find_local_users():
    users = db["users"]
    local_active = users.find({
        "$and": [
            {"city": {"$in": ["New York", "Los Angeles", "Chicago"]}},
            {"active": True},
            {"last_login": {"$exists": True}}
        ]
    })
    
    print("Active users in major cities:")
    for user in local_active:
        print(f"- {user['name']} from {user['city']}")

# Run examples
find_sale_items()
find_local_users()

🧠 Test Your Knowledge

Which operator finds values greater than 50?

How do you find documents where category is "books" OR "toys"?

Which finds names starting with "A"?