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Day 03 Applied Practice

Aggregation Pipelines

Transform and analyze data with $match, $group, $sort, $lookup, and $project stages.

~1 hour Hands-on Precision AI Academy

Today’s Objective

Transform and analyze data with $match, $group, $sort, $lookup, and $project stages.

The aggregation pipeline is like a series of Unix pipes. Each stage transforms the documents and passes results to the next stage.

Pipeline stages
PIPELINE STAGES
db.orders.aggregate([ // Stage 1: filter documents { $match: { status: 'completed' } }, // Stage 2: group and calculate { $group: { _id: '$category', totalRevenue: { $sum: '$amount' }, orderCount: { $count: {} }, avgOrder: { $avg: '$amount' } }}, // Stage 3: sort results { $sort: { totalRevenue: -1 } }, // Stage 4: limit { $limit: 10 }, // Stage 5: reshape output { $project: { _id: 0, category: '$_id', totalRevenue: 1, orderCount: 1, avgOrder: { $round: ['$avgOrder', 2] } }}
])
$lookup: Joins
$LOOKUP: JOINS
// Join users to their orders
db.orders.aggregate([ { $lookup: { from: 'users', localField: 'userId', foreignField: '_id', as: 'user' }}, { $unwind: '$user' },  // flatten the user array { $project: { orderId: '$_id', amount: 1, userName: '$user.name', userEmail: '$user.email' }}
])
📝 Day 3 Exercise
Build a Sales Report
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Supporting Resources

Go deeper with these references.

MongoDB Docs
Official MongoDB Manual Complete reference documentation for all MongoDB features and operations.
→
MongoDB University
Free MongoDB Courses Official free courses on MongoDB fundamentals, aggregation, and performance.
→
GitHub
MongoDB Driver Examples Official Node.js and Python driver examples on GitHub.
→

Day 3 Checkpoint

Before moving on, make sure you can answer these without looking:

Continue To Day 4
Indexes and Performance
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