Exercise 1: Publishing an Author's Drafts, All or Nothing — Possible Solution
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async function promoteAndPublish(authorId: number) {
  const [published, author] = await prisma.$transaction([
    prisma.post.updateMany({
      where: { authorId, published: false },
      data:  { published: true },
    }),
    prisma.user.update({
      where: { id: authorId },
      data:  { role: "AUTHOR" },
    }),
  ]);
  return { publishedCount: published.count, role: author.role };
}

Proving the rollback:

// Pick an author with drafts, note how many drafts they have
const before = await prisma.post.count({ where: { authorId: 3, published: false } });

try {
  await prisma.$transaction([
    prisma.post.updateMany({ where: { authorId: 3, published: false }, data: { published: true } }),
    prisma.user.update({ where: { id: 999999 }, data: { role: "AUTHOR" } }),  // no such user: P2025
  ]);
} catch (e) {
  console.log("Transaction failed:", (e as any).code);   // P2025
}

const after = await prisma.post.count({ where: { authorId: 3, published: false } });
console.log(before, after);   // the same number: the drafts were NOT published

WHY THIS WORKS AS AN ANSWER
------------------------------
Both changes are independent and known in advance, so the batch form
fits. Neither query is awaited inside the array; only $transaction is.
The test makes the second query fail with a record-not-found error and
then counts the drafts again — the count is unchanged, which shows the
first query was rolled back rather than left half-done.