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👐 $sort and $limit

🔹 $sort → Sorting results​

Syntax​

{
  $sort: {
    field: 1,
  }
}
  • { field: 1 } → Ascending order (A → Z, smallest to largest)
  • { field: -1 } → Descending order (Z → A, largest to smallest)
  • You can sort by multiple fields, just like SQL.

Example: Find the most recent reviews on our app.​

db.reviews.aggregate([
  {
    $sort: { timestamp: -1 },
  },
]);

Equivalent SQL query​

SELECT * FROM books ORDER BY timestamp DESC;

🔹 $limit → Limiting the number of results​

Syntax​

{
  $limit: n
}
  • n is the maximum number of documents you want in your results.

Example: Find the 5 most recent reviews on our app​

db.reviews.aggregate([
  {
    $sort: { timestamp: -1 },
  },
  {
    $limit: 5,
  },
]);

Equivalent SQL query​

SELECT * FROM books ORDER BY timestamp DESC LIMIT 5;

👐 Challenge​

👐 1. After the year 2000, which book has the most number of authors?​

Answer

There are 2 ways to solve this-

  • $project
  • $addFields
info

Learn when to use $addFields over $project

db.books.aggregate([
  {
    $match: { year: { $gt: 2000 } }
  },
  {
    $match: {
      authors: { $exists: true },
    }
  },
  {
    $addFields: {
      numAuthors: { $size: "$authors" },
    }
  },
  {
    $sort: { "numAuthors": -1 }
  },
  {
    $limit: 1
  }
]);