type-safety-validation

Type Safety & Validation

Overview

End-to-end type safety ensures bugs are caught at compile time, not runtime. This skill covers Zod for runtime validation, tRPC for type-safe APIs, Prisma for type-safe database access, and modern TypeScript features.

When to use this skill:

• Building type-safe APIs (REST, RPC, GraphQL)
• Validating user input and external data
• Ensuring database queries are type-safe
• Creating end-to-end typed full-stack applications
• Migrating from JavaScript to TypeScript
• Implementing strict validation rules

Core Stack

1. Zod - Runtime Validation

import { z } from 'zod'

// Define schema
const UserSchema = z.object({
  id: z.string().uuid(),
  email: z.string().email(),
  age: z.number().int().positive().max(120),
  role: z.enum(['admin', 'user', 'guest']),
  metadata: z.record(z.string()).optional(),
  createdAt: z.date().default(() => new Date())
})

// Infer TypeScript type from schema
type User = z.infer<typeof UserSchema>

// Validate data
const result = UserSchema.safeParse(data)
if (result.success) {
  const user: User = result.data
} else {
  console.error(result.error.issues)
}

// Transform data
const EmailSchema = z.string().email().transform(email => email.toLowerCase())

Advanced Patterns:

// Refinements
const PasswordSchema = z.string()
  .min(8)
  .refine((pass) => /[A-Z]/.test(pass), 'Must contain uppercase')
  .refine((pass) => /[0-9]/.test(pass), 'Must contain number')

// Discriminated Unions
const EventSchema = z.discriminatedUnion('type', [
  z.object({ type: z.literal('click'), x: z.number(), y: z.number() }),
  z.object({ type: z.literal('scroll'), offset: z.number() })
])

// Recursive Types
const CategorySchema: z.ZodType<Category> = z.lazy(() =>
  z.object({
    name: z.string(),
    children: z.array(CategorySchema).optional()
  })
)

2. tRPC - Type-Safe APIs

// Server: Define procedures
import { initTRPC } from '@trpc/server'
import { z } from 'zod'

const t = initTRPC.create()

export const appRouter = t.router({
  getUser: t.procedure
    .input(z.object({ id: z.string() }))
    .query(async ({ input }) => {
      return await db.user.findUnique({ where: { id: input.id } })
    }),

  createUser: t.procedure
    .input(z.object({
      email: z.string().email(),
      name: z.string()
    }))
    .mutation(async ({ input }) => {
      return await db.user.create({ data: input })
    })
})

export type AppRouter = typeof appRouter

// Client: Fully typed!
import { createTRPCProxyClient, httpBatchLink } from '@trpc/client'
import type { AppRouter } from './server'

const client = createTRPCProxyClient<AppRouter>({
  links: [httpBatchLink({ url: 'http://localhost:3000/api/trpc' })]
})

// TypeScript knows the exact shape!
const user = await client.getUser.query({ id: '123' })
//    ^? User | null