Exercise 3: Choosing the Right Method — Possible Solution
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(a) Show one post from its URL slug
    findUnique({ where: { slug } }) — slug is @unique, so this is the
    most direct lookup and returns null if there's no such post, which
    the page can turn into a "not found" message. (findUniqueOrThrow
    also works if you'd rather catch a P2025 error.)

(b) Find the most recent unpublished post
    findFirst — several posts may be unpublished, and you want just one,
    so it needs sorting too:
      findFirst({ where: { published: false }, orderBy: { createdAt: "desc" } })
    (orderBy is covered in Chapter 6.)

(c) Make sure an "about" page exists, creating it only if missing
    upsert({ where: { slug: "about" }, update: {},
             create: { title: "About", slug: "about" } })
    One call handles both cases. An empty update means an existing page
    is left alone.

(d) Clear all posts before a test run
    deleteMany({}) — the one time an empty where is exactly what you
    want. Only ever point this at a test database.

WHY THIS WORKS AS AN ANSWER
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Each choice follows from whether the lookup is by a unique field,
whether one or many records are affected, and whether the record might
not exist yet.