API Filtering & Sorting

Build flexible filtering and sorting systems that handle complex queries efficiently.

Query Parameter Syntax

GET /products?category=electronics&price[gte]=100&price[lte]=500&sort=-price,name

Implementation (Node.js)

const allowedFilters = ['category', 'status', 'price', 'createdAt'];
const allowedSorts = ['name', 'price', 'createdAt'];

app.get('/products', async (req, res) => {
  const filter = {};
  const sort = {};

  // Parse filters
  for (const [key, value] of Object.entries(req.query)) {
    if (key === 'sort') continue;

    const match = key.match(/^(\w+)\[(\w+)\]$/);
    if (match) {
      const [, field, operator] = match;
      if (!allowedFilters.includes(field)) continue;
      filter[field] = { [`$${operator}`]: parseValue(value) };
    } else if (allowedFilters.includes(key)) {
      filter[key] = value;
    }
  }

  // Parse sort
  if (req.query.sort) {
    for (const field of req.query.sort.split(',')) {
      const direction = field.startsWith('-') ? -1 : 1;
      const name = field.replace(/^-/, '');
      if (allowedSorts.includes(name)) sort[name] = direction;
    }
  }

  const products = await Product.find(filter).sort(sort);
  res.json({ data: products });
});

function parseValue(value) {
  if (value === 'true') return true;
  if (value === 'false') return false;
  if (!isNaN(value)) return Number(value);
  return value;
}

Filter Operators

Operator	Meaning	Example
eq	Equals	?status=active
ne	Not equals	?status[ne]=deleted
gt/gte	Greater than	?price[gte]=100
lt/lte	Less than	?price[lte]=500
in	In array	?status[in]=active,pending
like	Contains	?name[like]=phone

Security

• Whitelist allowed filter fields
• Validate input types per field
• Index frequently-filtered columns
• Limit query complexity
• Prevent SQL/NoSQL injection

Best Practices

• Support common operators
• Cache filter option lists
• Monitor query performance
• Provide sensible defaults