Mongoose how to write a query with if condition?

In Mongoose, multiple approaches can be used to incorporate if conditions in queries. Here are some common methods to implement conditional logic:

1. Using JavaScript's if Statement to Build Query Conditions

Before constructing the query, use JavaScript's if statement to dynamically add conditions based on logic. This method provides high flexibility, allowing you to dynamically construct queries based on complex logic.

javascript
const User = require('../models/User');

async function findUsers(ageLimit) {
  let query = User.find();

  if (ageLimit) {
    query = query.where('age').lte(ageLimit);
  }

  const results = await query.exec();
  return results;
}

// Usage example
findUsers(30).then(users => {
  console.log(users);
});

In this example, the age limit condition is only added when the ageLimit parameter is provided.

2. Using Query Builder's Chaining Syntax

Mongoose supports chaining syntax, enabling sequential addition of query conditions based on conditional checks.

javascript
const User = require('../models/User');

async function findUsers(options) {
  let query = User.find();

  if (options.age) {
    query = query.where('age').equals(options.age);
  }

  if (options.name) {
    query = query.where('name').equals(options.name);
  }

  const results = await query.exec();
  return results;
}

// Usage example
findUsers({ age: 25, name: 'John Doe' }).then(users => {
  console.log(users);
});

In this example, query conditions are dynamically added based on the properties of the options object passed in.

3. Using an Object to Build Conditions

Another method involves directly constructing a condition object during the query, with properties dynamically added based on if statements.

javascript
const User = require('../models/User');

async function findUsers(criteria) {
  let conditions = {};

  if (criteria.age) {
    conditions.age = { $lte: criteria.age };
  }

  if (criteria.name) {
    conditions.name = criteria.name;
  }

  const results = await User.find(conditions).exec();
  return results;
}

// Usage example
findUsers({ age: 30, name: 'Jane Doe' }).then(users => {
  console.log(users);
});

This approach centralizes all query conditions within a single object, resulting in cleaner and more maintainable code.

These are the common methods for using if conditions in Mongoose queries. Each method has specific use cases, and the choice depends on your requirements and personal preference.