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.agents/skills/prisma-database-setup/references/mongodb.md

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+# MongoDB Setup
+
+MongoDB projects should stay on the latest Prisma 6.x release. Do not upgrade a MongoDB app to Prisma 7's SQL client path.
+
+## Prerequisites
+
+- MongoDB 4.2+
+- Replica Set configured (required for transactions)
+- Latest Prisma 6.x release, or your team's pinned Prisma 6 version
+- Node.js 20.19.0+
+- TypeScript 5.4.0+
+
+## 1. Schema Configuration
+
+Use the standard Prisma 6 MongoDB setup with `prisma-client-js`.
+
+In `prisma/schema.prisma`:
+
+```prisma
+datasource db {
+  provider = "mongodb"
+  url      = env("DATABASE_URL")
+}
+
+generator client {
+  provider = "prisma-client-js"
+}
+```
+
+### Driver Adapters
+
+Do **not** apply the Prisma 7 SQL adapter setup here. MongoDB does not use a SQL `@prisma/adapter-*` package.
+
+### ID Field Requirement
+
+MongoDB models **must** have a mapped `_id` field using `@id` and `@map("_id")`, usually of type `String` with `auto()` and `db.ObjectId`.
+
+```prisma
+model User {
+  id    String @id @default(auto()) @map("_id") @db.ObjectId
+  email String @unique
+  name  String?
+}
+```
+
+### Relations
+
+Relations in MongoDB expect IDs to be `db.ObjectId` type.
+
+```prisma
+model Post {
+  id       String @id @default(auto()) @map("_id") @db.ObjectId
+  author   User   @relation(fields: [authorId], references: [id])
+  authorId String @db.ObjectId
+}
+```
+
+## 2. Environment Variable
+
+In `.env`:
+
+```env
+DATABASE_URL="mongodb+srv://user:password@cluster.mongodb.net/mydb?retryWrites=true&w=majority"
+```
+
+## Migrations vs Introspection
+
+- **No Migrations**: MongoDB is schema-less. `prisma migrate` commands **do not work**.
+- **db push**: Use `prisma db push` to sync indexes and constraints.
+- **db pull**: Use `prisma db pull` to generate schema from existing data (sampling).
+
+## Current Verification Notes
+
+- `prisma init --datasource-provider mongodb` is still implemented in Prisma's CLI source.
+- Prisma's upstream repo still contains MongoDB fixtures and tests.
+- Local verification shows Prisma 7 can still recognize MongoDB inputs, but the generated client path does not provide a supported MongoDB upgrade path.
+- Local verification shows Prisma 6.x works end to end with `prisma-client-js`, `prisma db push`, and `new PrismaClient()` against a MongoDB replica set.
+
+## Version Guidance
+
+- For MongoDB, stay on the latest available Prisma 6.x release.
+- Treat Prisma 7 MongoDB migration attempts as unsupported until Prisma ships a real MongoDB upgrade path.
+
+## Common Issues
+
+### "Transactions not supported"
+Ensure your MongoDB instance is a **Replica Set**. Standalone instances do not support transactions. Atlas clusters are replica sets by default.
+
+### "Invalid ObjectID"
+Ensure fields referencing IDs are decorated with `@db.ObjectId` if the target is an ObjectID.