Querying Across a Relationship

My latest feature change is relatively simple. The blog can now filter by tag - click "Prisma" and you get just the Prisma posts.

Posts and tags aren't a simple column

A post doesn't "have a tag" the way it has a title. It's a many-to-many relationship: a post can have many tags, and a tag belongs to many posts. Under the hood that lives in a separate join table — one row per post↔tag link — not a column on either side.

So "find posts tagged prisma" isn't a lookup on the posts table; it's a question about which posts are linked to that tag.

One line does the join

With Prisma, that reaching-across query is simple:

const posts = await prisma.post.findMany({
  where: {
    status: "PUBLISHED",
    tags: { some: { slug: "prisma" } },
  },
  orderBy: { publishedAt: "desc" },
});

I'm filtering Post by a condition on the related Tag, and Prisma turns that into a SQL join through the hidden join table. I never write the join myself, prisma does that for me.