# 4. Database Architecture (Revised with Prisma)

The database schema will be defined declaratively using the Prisma schema language in a single source of truth file: `prisma/schema.prisma`. Prisma will be responsible for generating SQL migrations and providing a type-safe client for all database interactions.

## Prisma Schema (`prisma/schema.prisma`)

```prisma
// This is your Prisma schema file,
// learn more about it in the docs: https://pris.ly/d/prisma-schema

generator client {
  provider = "prisma-client-js"
}

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
}

// User-friendly metadata associated with a public key.
model Registry {
  publicKey   String    @id
  citizenName String
  avatarUrl   String?
  isActive    Boolean   @default(true)
  createdAt   DateTime  @default(now())
}

// The core, immutable data model.
// Once a row is written, it is never updated or deleted.
model LedgerEntry {
  id                 BigInt    @id @default(autoincrement())
  previousHash       String?
  entryHash          String    @unique
  citizenPublicKey   String
  signature          String
  actionType         String
  payload            Json? // The actual data for the action, e.g., cell details
  createdAt          DateTime  @default(now())

  @@index([citizenPublicKey])
  @@index([payload], name: "idx_ledger_payload_entity") // Example for indexing specific payload keys
}
```

## Migrations Workflow

Database migrations will be managed exclusively by Prisma Migrate.
1.  **Development:** After any change to `schema.prisma`, a new migration will be created and applied using the command:
    ```bash
    npx prisma migrate dev --name <descriptive_migration_name>
    ```
2.  **Production:** Migrations will be applied during the deployment process using:
    ```bash
    npx prisma migrate deploy
    ```
This ensures that the database schema is always in sync with the Prisma schema definition.

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