How to use single validator class for both resource creation and modification in AdonisJS 5? - adonis.js

Question

Sometimes I may need to use single validator class for both inserting and updating resources, as opposed to this statement. Otherwise I may have duplicate codes, which inherently goes against DRY principle.
Consider the following case:
Say, I have a products resource in my app, and users of my app can create, update and delete products. Assume that the product model looks something like this:
export default class Product extends BaseModel {
#column({ isPrimary: true })
public id: number
#column()
public code: string
#column()
public title: string
#column()
public description: string
#column()
public price: number
}
Certainly the migration will be very close to the following:
export default class ProductsSchema extends BaseSchema {
protected tableName = 'products'
public async up() {
this.schema.createTable(this.tableName, (table) => {
table.increments('id').primary()
table.string('code').unique().notNullable() // <= pay attention that this field is unique
table.string('title').notNullable()
table.string('description', 25).notNullable()
table.double('price').notNullable()
})
}
public async down() {
this.schema.dropTable(this.tableName)
}
}
Now users will create a new product. So they will be presented a form, and the validation may look something like:
export default class ProductCreateValidator {
constructor(protected ctx: HttpContextContract) {}
public schema = schema.create({
code: schema.string({ trim: true, escape: true }, [
rules.unique({ table: 'products', column: 'code' }),
]), // <= because this field is unique inside the database
title: schema.string({ trim: true, escape: true }, [
rules.alpha({ allow: ['space'] }),
]),
description: schema.string({ trim: true, escape: true }),
price: schema.number(),
})
public cacheKey = this.ctx.routeKey
public messages = {}
}
The fun begins now! If I create separate class for updating products, most the fields will be the same, except code. So I'll have to duplicate the whole class:
export default class ProductUpdateValidator {
constructor(protected ctx: HttpContextContract) {}
public schema = schema.create({
code: schema.string({ trim: true, escape: true }, [
// rules.unique({ table: 'products', column: 'code' }),
]), // <= I cannot apply unique rule here - because I won't be able to update anymore
title: schema.string({ trim: true, escape: true }, [
rules.alpha({ allow: ['space'] }),
]),
description: schema.string({ trim: true, escape: true }),
price: schema.number(),
})
public cacheKey = this.ctx.routeKey
public messages = {}
}
What if I want to add 3 more fields? With this current setup, I'd have to go to these two class files and add those fields in both of them. And I'd have to go to both these files if I want to adjust some validation logic. It'd be much easier to maintain if I'd be able to use single class for both create and update actions; and it'd automatically cancel the uniqueness check if the particular field of the product that users trying to update hasn't been changed. How could that even possible?

Answer 1

It's very easy to achieve. We need to drop one validator class and modify the other one like so:
export default class ProductValidator {
constructor(protected ctx: HttpContextContract) {}
public schema = schema.create({
code: schema.string({ trim: true, escape: true }, [
rules.unique({
table: 'products',
column: 'code',
whereNot: {
id: this.ctx.request.input('id') || 0 // <= or this may come from route params: this.ctx.params.id
}
}),
]),
title: schema.string({ trim: true, escape: true }, [
rules.alpha({ allow: ['space'] }),
]),
description: schema.string({ trim: true, escape: true }),
price: schema.number(),
})
public cacheKey = this.ctx.routeKey
public messages = {}
}
Let's break this code down:
For inserting new product, the this.ctx.request.input('id') will be undefined, so it'll fallback to 0. So it'll perform SELECT code FROM products WHERE code = ? AND NOT id = ? query with ['<whatever_user_types>', 0]. Since id is the primary key for that table and it cannot be 0, the later condition of the query above will always be TRUE. So the validator will only throw error if the code is found (since the later part is already TRUE). Hence our objective is fulfilled.
For updating existing product, you'll certainly have the ID of the product in hand. Because you're fetching the product from the database, you certainly know its ID. Now put it somewhere of your choice (either inside the update form as <input type="hidden" name="id" value="{{ product.id }}"> or as route param /products/:id/update). Since we have the ID this time around, the this.ctx.request.input('id') (or this.ctx.params.id) will be set. So the query will look like SELECT code FROM products WHERE code = ? AND NOT id = ? query with ['<whatever_user_types>', <product_id>]. This time, the later condition of the query will always be FALSE, so it won't complain if the code matches only with the product we're trying to update and not with any other products. Bingo!
So this is how you can avoid code duplication by utilizing single validator for both create and update actions. Let me know down in comments if you have any other questions.