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Day 2 of 5
⏱ ~60 minutes
MongoDB in 5 Days — Day 2

Queries and Operators

Comparison, logical, and array operators. Projection, sort, skip, and limit.

Query Operators

Comparison Operators
// Numeric comparisons
db.products.find({ price: { $gt: 100 } })    // > 100
db.products.find({ price: { $gte: 100 } })   // >= 100
db.products.find({ price: { $lt: 50 } })     // < 50
db.products.find({ price: { $ne: 0 } })      // != 0
db.products.find({ category: { $in: ['Electronics', 'Books'] } })
db.products.find({ category: { $nin: ['Food'] } })
Logical Operators
// AND (implicit — just combine conditions)
db.products.find({ price: { $lt: 100 }, inStock: true })

// Explicit AND
db.products.find({ $and: [
  { price: { $lt: 100 } },
  { category: 'Electronics' }
]})

// OR
db.products.find({ $or: [
  { price: { $lt: 10 } },
  { featured: true }
]})

// NOT
db.products.find({ category: { $not: { $eq: 'Food' } } })
Projection, Sort, Limit
// Projection: 1 = include, 0 = exclude
db.products.find({}, { name: 1, price: 1, _id: 0 })

// Sort: 1 = ascending, -1 = descending
db.products.find().sort({ price: -1 })

// Pagination
const PAGE = 2;
const PER_PAGE = 10;
db.products.find()
  .sort({ createdAt: -1 })
  .skip((PAGE - 1) * PER_PAGE)
  .limit(PER_PAGE)
📝 Day 2 Exercise
Build Pagination
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Day 2 Summary

  • Comparison: $gt, $gte, $lt, $lte, $ne, $in, $nin.
  • Logical: $and (implicit with multiple conditions), $or, $not.
  • Projection: { field: 1 } to include, { field: 0 } to exclude. Can't mix include/exclude.
  • .sort().skip().limit() chain for pagination.
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Day 1: Documents, Collections, and CRUD
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Day 3: Aggregation Pipelines
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