Exercise 1: Adding Comments — Possible Solution
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// POST /posts/:slug/comments   { "body": "...", "authorEmail": "optional" }
app.post("/posts/:slug/comments", async (req, res) => {
  const body = String(req.body.body ?? "").trim();
  const authorEmail = req.body.authorEmail ? String(req.body.authorEmail) : undefined;
  if (!body) return res.status(400).json({ error: "body is required" });

  const post = await prisma.post.findFirst({
    where: { slug: req.params.slug, published: true },
    select: { id: true },
  });
  if (!post) return res.status(404).json({ error: "Post not found" });

  const comment = await prisma.comment.create({
    data: {
      body,
      post: { connect: { id: post.id } },
      ...(authorEmail ? { author: { connect: { email: authorEmail } } } : {}),
    },
    select: { body: true, createdAt: true, author: { select: { name: true } } },
  });
  res.status(201).json(comment);
});

Notes:

  - The post is looked up with findFirst so drafts are treated as
    missing, matching GET /posts/:slug.
  - The author is only connected when an email is given; otherwise
    the optional relation stays empty and it's a guest comment.
  - An unknown authorEmail makes the connect fail, and the error
    handler turns that into a 404, since connect requires the record
    to exist.
  - Only safe fields are returned, as elsewhere in the API.

WHY THIS WORKS AS AN ANSWER
------------------------------
It uses nested connects for both relations, handles the optional
author cleanly, and reuses the course's patterns for 404s and select.