Custom validation rules

Summary

Aside from using regex for validation, Sails also allows custom validation functions. These functions take a value and return true (valid) or false (invalid), making them highly flexible for unique business rules.

Transcript

For example, suppose your app is only available in Nigeria, Kenya, and Ghana. You can enforce this rule using a custom validation function.

Example: Restricting Signups to Specific Countries

In your Sails model, define the country attribute like this:

country: {
  type: 'string',
  custom: (value) => ['Nigeria', 'Kenya', 'Ghana'].includes(value),
}

Key takeaways:

✅ Custom validation functions allow more flexibility than built-in rules.
✅ The function receives the value and must return true or false.
✅ Works for all data types (string, number, JSON, boolean, etc.).

Testing the Validation Rule

1. Invalid Country

await User.create({ country: "Uganda" });

❌ Fails, because Uganda is not in the allowed list.

2. Valid Country

await User.create({ country: "Nigeria" });

✅ Passes, because Nigeria is in the allowed list.

3. Testing All Allowed Countries

await User.create({ country: "Kenya" });  // ✅ Passes  
await User.create({ country: "Ghana" });  // ✅ Passes  

When to Use custom Validation

• Business logic rules (e.g., allowed countries, age limits, company-specific validation).

• More complex conditions (e.g., cross-field validation, checking external APIs).

• Fallback when built-in rules are insufficient.

Next Up:

• When to use validation rules