Add full text search example (#9807)

Author: borisno2

examples/extend-full-text-search/README.md

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+## Feature Example - Prisma Full-Text Search (PostgreSQL)
+
+This project demonstrates how to use [Prisma's Full-Text Search](https://www.prisma.io/docs/v6/orm/prisma-client/queries/full-text-search) on PostgreSQL with Keystone, using `extendPrismaSchema` to enable the `fullTextSearchPostgres` preview feature and a custom GraphQL query to expose it.
+
+> **Note:** This example requires a running PostgreSQL database. Full-text search is not available on SQLite.
+
+## Instructions
+
+To run this project, clone the Keystone repository locally then run `pnpm install` at the root of the repository.
+
+Set your database URL:
+
+```shell
+export DATABASE_URL="postgresql://localhost/keystone-example"
+```
+
+Then navigate to this directory and run:
+
+```shell
+pnpm dev
+```
+
+This will start the Admin UI at [localhost:3000](http://localhost:3000).
+You can use the Admin UI to create items in your database.
+
+You can also access a GraphQL Playground at [localhost:3000/api/graphql](http://localhost:3000/api/graphql), which allows you to directly run GraphQL queries and mutations.
+
+## Features
+
+### Enabling Full-Text Search with `extendPrismaSchema`
+
+Prisma's `fullTextSearchPostgres` is a [preview feature](https://www.prisma.io/docs/v6/orm/reference/preview-features/client-preview-features) that must be explicitly enabled in the Prisma generator block. Since Keystone manages the `schema.prisma` file automatically, you can inject this using `extendPrismaSchema` in your Keystone config:
+
+```typescript
+db: {
+  provider: 'postgresql',
+  extendPrismaSchema: schema => {
+    return schema.replace(
+      /(generator [^}]+)}/g,
+      ['$1', '  previewFeatures = ["fullTextSearchPostgres"]', '}'].join('\n')
+    )
+  },
+}
+```
+
+This produces a generator block like:
+
+```prisma
+generator client {
+  provider        = "prisma-client-js"
+  previewFeatures = ["fullTextSearchPostgres"]
+}
+```
+
+### Custom `searchPosts` Query
+
+Prisma's `search` operator is a low-level Prisma feature not yet surfaced through Keystone's `context.db` query layer. To use it, the example reaches for the raw Prisma client via `context.prisma`, then converts the results back to Keystone-typed objects using `context.db`:
+
+```typescript
+// 1. Use raw Prisma client to perform the full-text search
+const matches = await context.prisma.post.findMany({
+  where: {
+    OR: [{ title: { search: query } }, { content: { search: query } }],
+  },
+  select: { id: true },
+})
+
+// 2. Fetch proper Keystone Post objects using the matched IDs
+const ids = matches.map(p => p.id)
+return context.db.Post.findMany({ where: { id: { in: ids } } })
+```
+
+### PostgreSQL Full-Text Search Syntax
+
+The `query` argument accepts PostgreSQL's tsquery syntax:
+
+| Operator | Meaning          | Example                                                 |
+| -------- | ---------------- | ------------------------------------------------------- |
+| `&`      | AND              | `"cat & dog"` — must contain both                       |
+| `\|`     | OR               | `"cat \| dog"` — must contain either                    |
+| `!`      | NOT              | `"!cat"` — must not contain                             |
+| `<->`    | Phrase/proximity | `"fox <-> dog"` — "dog" follows immediately after "fox" |
+
+### Try it in the GraphQL Playground
+
+After creating some posts in the Admin UI, open [localhost:3000/api/graphql](http://localhost:3000/api/graphql) and run:
+
+```graphql
+query {
+  searchPosts(query: "keystone & graphql") {
+    id
+    title
+    content
+    author {
+      name
+    }
+  }
+}
+```
+
+## Try it out in CodeSandbox 🧪
+
+You can play with this example online in a web browser using the free [codesandbox.io](https://codesandbox.io/) service. To launch this example, open the URL <https://githubbox.com/keystonejs/keystone/tree/main/examples/extend-full-text-search>. You can also fork this sandbox to make your own changes.

examples/extend-full-text-search/keystone.ts

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+import { config } from '@keystone-6/core'
+import { lists, extendGraphqlSchema } from './schema'
+
+export default config({
+  db: {
+    provider: 'postgresql',
+    url: process.env.DATABASE_URL || 'postgresql://localhost/keystone-example',
+
+    extendPrismaSchema: schema => {
+      return schema.replace(
+        /(generator [^}]+)}/g,
+        ['$1', '  previewFeatures = ["fullTextSearchPostgres"]', '}'].join('\n')
+      )
+    },
+
+    // WARNING: this is only needed for our monorepo examples, dont do this
+    prismaClientPath: 'node_modules/myprisma',
+  },
+  graphql: {
+    extendGraphqlSchema,
+  },
+  lists,
+})

examples/extend-full-text-search/package.json

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+{
+  "name": "@keystone-6/example-extend-full-text-search",
+  "version": null,
+  "private": true,
+  "license": "MIT",
+  "scripts": {
+    "dev": "keystone dev",
+    "start": "keystone start",
+    "build": "keystone build",
+    "postinstall": "keystone postinstall"
+  },
+  "dependencies": {
+    "@keystone-6/core": "^6.5.2",
+    "@prisma/client": "6.16.1"
+  },
+  "devDependencies": {
+    "prisma": "6.16.1",
+    "typescript": "^5.9.0"
+  }
+}

examples/extend-full-text-search/sandbox.config.json

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+{
+  "template": "node",
+  "container": {
+    "startScript": "keystone dev",
+    "node": "22"
+  }
+}