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Pagination & Filtering

  • Pagination, filtering, and sorting help APIs efficiently manage and return structured data from large datasets.
  • 🔹 Pagination Techniques


     Pagination is the process of dividing large datasets into smaller, manageable pages so the client receives limited data per request.

    🧠 Why Pagination is Important

    • Faster API responses

    • Reduced server load

    • Better UI performance (especially tables & lists)

    • Essential for real-world applications

    🔹 Common Pagination Parameters

    Parameter

    Purpose

    page

    Current page number

    limit

    Records per page

    skip

    Number of records to skip


    🧪 Example – Basic Pagination (MongoDB + Mongoose)

Pagination Techniques in APIs

Pagination divides large datasets into smaller pages to improve API performance, reduce server load, and deliver faster, user-friendly responses using parameters like page, limit, and skip. 

const getUsers = async (req, res) => {
  const page = parseInt(req.query.page) || 1;
  const limit = parseInt(req.query.limit) || 10;

  const skip = (page - 1) * limit;

  const users = await User.find()
    .skip(skip)
    .limit(limit);

  res.json({
    page,
    limit,
    totalUsers: await User.countDocuments(),
    data: users
  });
};

  • Explanation:

    • page=1&limit=10 → First 10 records

    • page=2&limit=10 → Next 10 records

    🔹 Filtering Data

    Filtering allows clients to retrieve specific records based on conditions like name, status, category, or price.

    Example – Filtering by Field

Filtering Data in APIs

Filtering allows clients to fetch specific records based on query parameters like category or availability, returning only relevant data from the server. 

const getProducts = async (req, res) => {
  const filter = {};

  if (req.query.category) {
    filter.category = req.query.category;
  }

  if (req.query.inStock) {
    filter.inStock = req.query.inStock === "true";
  }

  const products = await Product.find(filter);
  res.json(products);
};
  • Request Example:

/api/products?category=electronics&inStock=true
  • 🔹 Sorting Data


     Sorting arranges data in ascending or descending order based on fields like date, price, or name.

    Example – Sorting with Query Params


Sorting Data in APIs

Sorting organizes API response data in ascending or descending order using query parameters, allowing clients to control how results are displayed. 

const sortField = req.query.sortBy || "createdAt";
const sortOrder = req.query.order === "asc" ? 1 : -1;

const products = await Product.find()
  .sort({ [sortField]: sortOrder });

res.json(products);
  • Request Example:

/api/products?sortBy=price&order=asc
  • 🔹 Combining Pagination + Filtering + Sorting

    Real-World API Pattern


const getAllProducts = async (req, res) => {
  const page = parseInt(req.query.page) || 1;
  const limit = parseInt(req.query.limit) || 5;
  const skip = (page - 1) * limit;

  const filter = {};
  if (req.query.category) {
    filter.category = req.query.category;
  }

  const sortBy = req.query.sortBy || "createdAt";
  const order = req.query.order === "asc" ? 1 : -1;

  const products = await Product.find(filter)
    .sort({ [sortBy]: order })
    .skip(skip)
    .limit(limit);

  const total = await Product.countDocuments(filter);

  res.json({
    page,
    totalPages: Math.ceil(total / limit),
    totalRecords: total,
    data: products
  });
};
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