Dynamic Metadata with generateMetadata

// app/blog/[slug]/page.tsx

import type { Metadata } from 'next';

type PageProps = {
  params: Promise<{
    slug: string;
  }>;
};

async function getPost(slug: string) {
  return db.post.findUnique({
    where: { slug },
    select: {
      title: true,
      excerpt: true,
    },
  });
}

export async function generateMetadata({
  params,
}: PageProps): Promise<Metadata> {
  const { slug } = await params;
  const post = await getPost(slug);

  if (!post) {
    return {
      title: 'Post not found',
    };
  }

  return {
    title: post.title,
    description: post.excerpt,
    alternates: {
      canonical: `/blog/${slug}`,
    },
    openGraph: {
      title: post.title,
      description: post.excerpt,
      type: 'article',
    },
  };
}