TypeScriptpost-schema.ts
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import { z } from 'zod';
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// Schema = runtime validation + static type (single source of truth)
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const CreatePostSchema = z.object({
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  title: z.string().min(3).max(200),
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  body: z.string().min(10).max(10000),
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  tags: z.array(z.string().min(1).max(50)).max(10).default([]),
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  published: z.boolean().default(false),
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  authorId: z.string().uuid(),
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});
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const UpdatePostSchema = CreatePostSchema.partial().omit({ authorId: true });
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// Types derived from schemas — never write them twice
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type CreatePostDto = z.infer<typeof CreatePostSchema>;
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type UpdatePostDto = z.infer<typeof UpdatePostSchema>;
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// Simulated repository
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const posts: Array<CreatePostDto & { id: string; createdAt: Date }> = [];
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// Validate and create
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function createPost(raw: unknown): { success: true; post: typeof posts[0] } | { success: false; errors: Record<string, string> } {
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  const result = CreatePostSchema.safeParse(raw);
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  if (!result.success) {
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    const errors: Record<string, string> = {};
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    result.error.issues.forEach(issue => {
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      const path = issue.path.join('.');
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      errors[path] = issue.message;
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    });
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    return { success: false, errors };
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  }
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  const post = { ...result.data, id: crypto.randomUUID(), createdAt: new Date() };
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  posts.push(post);
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  return { success: true, post };
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}
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// Test
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const r1 = createPost({ title: 'Hi', body: 'Short', authorId: 'not-uuid' });
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console.log(r1); // { success: false, errors: { title: '...', body: '...', authorId: '...' } }
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const r2 = createPost({
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  title: 'TypeScript Deep Dive',
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  body: 'TypeScript is a superset of JavaScript that adds static typing...',
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  authorId: 'f47ac10b-58cc-4372-a567-0e02b2c3d479',
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});
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console.log(r2); // { success: true, post: { id: '...', title: '...', ... } }