19.md

19. Problem: Mongoose Validation

Problem Statement: Enhance the user schema from the previous question to include validation for the "email" property (must be a valid email address). Implement a function to add a new user to the MongoDB database with validation.

Function Signature:

/**
 * Adds a new user to the MongoDB database with validation
 * @param {Object} user - User object with properties username and email
 */
function addUserWithValidation(user) {
  // Your implementation here
}

Expected Output:

• If the user is successfully added, log a success message. If validation fails, log an error message.

Test Cases:

1. Call addUserWithValidation({ username: 'john_doe', email: 'invalid-email' }) and check the server logs for a validation error message.

Hint:

1. Define a Mongoose schema for the user with validation rules for the "email" property. Use the validate option to specify a custom validator function for the email format.

2. Create a Mongoose model using the schema.

3. Write a function addUserWithValidation that takes a user object, creates a new user instance using the Mongoose model, and attempts to save it to the database. Handle the validation errors and success cases appropriately.

Hints:

• Use the mongoose.Schema constructor to define the schema with validation rules. Use the validate option to specify a custom validator function for the "email" property.
• Use the mongoose.model method to create a model from the schema.
• In the addUserWithValidation function, create a new user instance using the model constructor and the provided user object.
• Use the save method on the user instance to save it to the database. Use a callback function to handle the result of the save operation. If there is an error, log the error message. If the user is saved successfully, log a success message.