How does the MongoDB Aggregation Pipeline work?

Explanation & Concept

The Aggregation Pipeline is a multi-stage framework for data transformation and analytics in MongoDB. Documents pass through sequential stages that filter, group, project, sort, and reshape the data stream.

Common stages include: • `$match`: Filters documents (analogous to SQL WHERE). • `$group`: Aggregates values by a specified key (analogous to SQL GROUP BY). • `$project`: Reshapes document fields (analogous to SQL SELECT). • `$unwind`: Deconstructs an array field into individual documents. • `$lookup`: Performs left outer joins to another collection.

Code Example

javascript

db.orders.aggregate([
  // Stage 1: Filter to completed orders from 2026
  { $match: { status: "COMPLETED", orderDate: { $gte: new Date("2026-01-01") } } },
  
  // Stage 2: Group by customerId and sum their spending
  { 
    $group: {
      _id: "$customerId",
      totalSpent: { $sum: "$totalAmount" },
      orderCount: { $sum: 1 }
    }
  },
  
  // Stage 3: Keep only high-value customers
  { $match: { totalSpent: { $gte: 1000 } } },
  
  // Stage 4: Sort descending by total revenue
  { $sort: { totalSpent: -1 } }
]);

How It Works & Key Takeaways

Each stage takes the output of the preceding stage. Memory is optimized because filtering occurs early in the pipeline via `$match`.

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javascript

How does the MongoDB Aggregation Pipeline work?

Explanation & Concept

Code Example

javascript

db.orders.aggregate([
  // Stage 1: Filter to completed orders from 2026
  { $match: { status: "COMPLETED", orderDate: { $gte: new Date("2026-01-01") } } },
  
  // Stage 2: Group by customerId and sum their spending
  { 
    $group: {
      _id: "$customerId",
      totalSpent: { $sum: "$totalAmount" },
      orderCount: { $sum: 1 }
    }
  },
  
  // Stage 3: Keep only high-value customers
  { $match: { totalSpent: { $gte: 1000 } } },
  
  // Stage 4: Sort descending by total revenue
  { $sort: { totalSpent: -1 } }
]);

How It Works & Key Takeaways

Each stage takes the output of the preceding stage. Memory is optimized because filtering occurs early in the pipeline via `$match`.

Mock Test · 1 Questions · Optional

Ready for Indexing Strategies?

Take a quick test to evaluate yourself, or move straight to the next module.

Beginner1 questions

Skip