Validation Classes

There are three built-in validation classes in Formn, each of which extends the ModelValidator base class.

• InsertModelValidator: Used to validate a model prior to inserting it.
• UpdateModelValidator: Used to validate a model before updating by ID.
• DeleteModelValidator: Used to validate a model before deleting by ID.

All three classes work the same way: instantiate the class, then call the validate method with two arguments.

1. An object to validate. This can be a plain JavaScript object, like an object from an API request, or an instance of a class.
2. The constructor of a Table-decorated class, a.k.a. an “Entity.” The first parameter–the object–will be checked against the Entity’s metadata to ensure that it’s acceptable for the requested CRUD operation.

The validate method returns a Promise that is resolved if the object is valid, or otherwise rejected with an error describing why the object is invalid.

In code terms, here’s how validation looks.

import { InsertModelValidator } from 'formn';

import { PhoneNumber } from '../entity/phone-number.entity';

const validator = new InsertModelValidator();

const phone = {
  personId:    1,
  phoneNumber: '530-222-3333',
  type:        'mobile'
};

// Validate "phone" against the "PhoneNumber" entity, ensuring that "phone" can
// be inserted.
validator
  .validate(phone, PhoneNumber)
  .then(() => console.log('Object is valid.'))
  .catch(err => console.error('Object is invalid: ', err));

Column Metadata

Back in the Models section, we defined a PhoneNumber class and decorated each property with the Column decorator. Column takes a ColumnMetaOptions object as an argument, which provides metadata about each property’s corresponding database column, like the data type, maximum length, nullability, and so on. Let’s look more closely at the PhoneNumber.phoneNumber property.

@Column({isNullable: false, maxLength: 255, sqlDataType: 'varchar'})
@Validate(new PhoneValidator())
phoneNumber: string;

That given, Formn knows that the phoneNumber property must be a string, it must not exceed 255 characters, and it cannot be null. There’s also some custom, user-defined validation provided by the bsy-validation package. Namely, we’ve specified that the phoneNumber property should go through bsy-validation’s PhoneValidator.

Next up, we’ll describe how the validation classes work in detail, and look over some examples.