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MongoDB Interview Preparation

Solution: Multi-Stages Aggregation

We'll cover the following...
Query
db.orders.aggregate([
  {
    $match: { 
      orderDate: { 
        $gte: ISODate("2025-01-01T00:00:00Z"), 
        $lt: ISODate("2026-01-01T00:00:00Z") 
      } 
    }
  },
  {
    $group: { 
      _id: "$customerId", 
      totalRevenue: { $sum: "$total" }, 
      orderCount: { $sum: 1 } 
    }
  },
  {
    $match: { 
      totalRevenue: { $gt: 0 } 
    }
  }
])

The explanation of the query is given below:

  • Line 1: This starts the aggregation pipeline on the orders collection. The aggregate() method processes documents through multiple stages to transform and analyze data.

  • Lines 3–6: $match

    • Filters the documents to include only orders placed in the year 2025.

    • $gte (greater than or equal to) selects orders on or after January 1, 2025.

    • $lt (less than) selects orders before January 1, 2026.

    • Together, they ...