Data Validation Layer

You are a backend developer building database safety. The user wants to create a validation layer that checks data integrity before any database operation.

What to check first

• Verify your database driver is installed: npm list (check for pg, mysql2, mongodb, etc.)
• Check if you have a validation library available: npm list joi or npm list zod
• Identify your database schema structure and required fields

Steps

1. Install a validation library: npm install joi (or use built-in Node.js validation)
2. Define a schema object that matches your database table structure with field types and constraints
3. Create a validation function that accepts raw user input before it reaches your database
4. Call .validate() on the schema with the incoming data object
5. Check the validation result for errors using .error property
6. Return early with validation error details if validation fails
7. Only proceed with the database INSERT/UPDATE operation if validation passes
8. Log validation failures for debugging and security auditing

Code

const Joi = require('joi');

// Define your validation schema
const userSchema = Joi.object({
  email: Joi.string()
    .email()
    .required()
    .messages({ 'string.email': 'Must be a valid email' }),
  
  password: Joi.string()
    .min(8)
    .required()
    .pattern(/[A-Z]/)
    .messages({ 'string.pattern.base': 'Password must contain uppercase' }),
  
  age: Joi.number()
    .integer()
    .min(18)
    .max(120)
    .optional(),
  
  name: Joi.string()
    .trim()
    .required()
    .max(100),
  
  phone: Joi.string()
    .pattern(/^\d{10}$/)
    .optional()
    .messages({ 'string.pattern.base': 'Phone must be 10 digits' })
});

// Create validation middleware/function
async function validateAndSaveUser(userData, db) {
  // Validate against schema
  const { error, value } = userSchema.validate(userData, {
    abortEarly: false,
    stripUnknown: true
  });
  
  if (error) {
    const validationErrors = error.details.map(detail => ({
      field: detail.path[0],
      message: detail.message
    }));
    return {
      success: false,
      errors: validationErrors
    };
  }
  
  try {
    // Only reach database if validation passed
    const result = await db.query(
      'INSERT INTO users (email, password, age, name, phone) VALUES ($1, $2, $3, $4, $5) RETURNING id',
      [value.email, value.password, value.age, value.name, value.phone]
    );
    
    return {
      success:

Note: this example was truncated in the source. See the GitHub repo for the latest full version.

Common Pitfalls

• Treating this skill as a one-shot solution — most workflows need iteration and verification
• Skipping the verification steps — you don't know it worked until you measure
• Applying this skill without understanding the underlying problem — read the related docs first

When NOT to Use This Skill

• When a simpler manual approach would take less than 10 minutes
• On critical production systems without testing in staging first
• When you don't have permission or authorization to make these changes

How to Verify It Worked

• Run the verification steps documented above
• Compare the output against your expected baseline
• Check logs for any warnings or errors — silent failures are the worst kind

Production Considerations

• Test in staging before deploying to production
• Have a rollback plan — every change should be reversible
• Monitor the affected systems for at least 24 hours after the change