Campus marketplace

Students sell textbooks, phones and tutoring to each other. Listings have photos and a price, buyers and sellers agree a deal, and moderators remove what should not be there.

New here: a table that points at itself, a resource whose whole job is to hold several of something, and ratings.

Read lost and found first for the conventions these pages share.

Resource	What it holds
Category	Nested: Electronics → Phones → Accessories
Listing	One thing for sale, with a price and a condition
ListingPhoto	One image; a listing has many
Deal	A buyer and a seller agreeing a price
Review	A rating left after a deal — one per deal
Report	Somebody flagging a listing

1. The app

Next.js

pnpm create flare-framework marketplace
cd marketplace
docker compose up -d

Cloudflare

pnpm create flare-framework marketplace --stack cloudflare
cd marketplace

2. Categories that nest

npx flare gen resource Category --icon tags --group Catalogue \
  --fields 'name:string!, parent:belongsTo(Category)?'

A belongsTo pointing at its own resource. Optional, because the top of the tree has no parent — a required self-reference is a table in which no row can ever be the first.

What it writes is worth looking at:

parentId: text("parent_id").references((): AnySQLiteColumn => categories.id, { onDelete: "set null" }),

The onDelete: "set null" is the useful part. Delete Electronics and its children are promoted to the top rather than deleted with it or blocking the delete. The lazy type annotation is what TypeScript needs for a table that refers to itself while it is still being defined.

The admin gives you a category picker on the category form, which is exactly right: that is how you say Phones sits under Electronics.

3. Listings

npx flare gen resource Listing --icon store --group Market \
  --fields 'title:string, description:markdown?, price:money, condition:enum(new,likeNew,good,fair), status:enum(draft,live,sold,removed), sellerId:string, category:belongsTo(Category)'

status:enum(draft,live,sold,removed) is a workflow in one field, and the database refuses a fifth value — so a typo in a script you write next year fails loudly instead of quietly adding a status nothing handles.

price:money is stored in whole minor units. See the library for why that matters more than it sounds.

4. Several photos

A file field holds one file. A listing wants five. So the photos are their own resource:

npx flare gen resource ListingPhoto --icon image --group Market \
  --fields 'image:file:[image]:5mb, primary:boolean, listing:belongsTo(Listing)'

This is the shape to reach for whenever “many of X” has anything else to say about each one — which photo is the cover, what order they go in, who uploaded it. A column holding a list of URLs cannot answer any of that and has to be migrated the day you ask.

5. Deals and reviews

npx flare gen resource Deal --icon handshake --group Market \
  --fields 'agreedPrice:money, status:enum(pending,completed,cancelled), completedAt:datetime?, buyerId:string, listing:belongsTo(Listing)'

npx flare gen resource Review --icon star --group Market \
  --fields 'rating:rating, comment:text?, reviewerId:string, deal:belongsTo(Deal)!'

Two things:

rating:rating is an integer 1–5 that renders as stars you click, rather than a number box you type 7 into.

deal:belongsTo(Deal)! — the ! makes it unique, which is the whole of “one review per deal”. Without it the same transaction can be reviewed five times by the same person, and a rating average stops meaning anything. A unique belongsTo is how you write one-to-one.

Found while writing this page

Seeding this resource used to fail. A unique belongsTo went through the same “make it unique” step as an email address, which appended a row number to the parent’s id — so the foreign key pointed at nothing. And rating seeded values up to 1000. Both are fixed; the page is here because building the project is what found them.

6. Moderation

npx flare gen resource Report --icon flag --group Moderation \
  --fields 'reason:enum(spam,counterfeit,prohibited,other), detail:text if reason == other, status:enum(open,upheld,dismissed), reportedById:string, handledById:string?, listing:belongsTo(Listing)'

detail:text if reason == other — the box appears only when the reason is “other”, is required only then, and is cleared if the reason changes to one of the named ones. A stale “other” explanation sitting on a report reclassified as spam is the kind of thing nobody notices until an audit.

7. Run it

npx flare migrate
npx flare seed:resource Category 12
npx flare seed:resource Listing 60
npx flare seed:resource Deal 25
npx flare seed:resource Review 20
npx flare dev

What you still owe

• Chat between buyer and seller. The brief asks for real-time. On Cloudflare that is Durable Objects and the realtime support Flare already has; on Next.js, polling or a third-party socket service. Model it as Conversation and Message resources and put the transport on top.
• Search with filters. The generated table filters and sorts out of the box. Searching descriptions properly needs a real index.
• Favourites. A junction: Favourite with listingId and a userId:string. Make the pair unique so one person cannot favourite the same listing twice.
• The seller’s rating. An average over their reviews — a computed field or a maintained column, and the difference between the two is a good thing to write about.
• Price negotiation, which is really a small offer workflow.

Make it yours

• Sellers edit only their own listings. npx flare gen policy Listing --roles '*' --own sellerId --own-except moderator,admin
• Soft delete for removed listings, so moderation is reversible: pass --soft-delete when generating Listing.
• Hide the photo rows from the sidebar with an admin-only policy on ListingPhoto, the same way the library hides its junction.