# Multi-Tenant Migration Guide

## Overview

This guide walks you through migrating existing services from the single-database architecture to the new multi-database per-tenant architecture.

## Architecture Comparison

### Before (Single Database)

```typescript
// Single Prisma client, data segregated by tenantId column
@Injectable()
export class UserService {
  constructor(private prisma: PrismaService) {}

  async findUserByEmail(tenantId: string, email: string) {
    return this.prisma.user.findFirst({
      where: { tenantId, email },
    });
  }
}
```

### After (Multi-Database)

```typescript
// Dynamic Knex connection per tenant, complete database isolation
@Injectable()
export class UserService {
  constructor(private tenantDb: TenantDatabaseService) {}

  async findUserByEmail(tenantId: string, email: string) {
    const knex = await this.tenantDb.getTenantKnex(tenantId);
    return User.query(knex).findOne({ email });
  }
}
```

## Step-by-Step Service Migration Examples

See full examples in the file for:

- AuthService migration
- RBACService migration
- ObjectService migration
- Controller updates
- Common query patterns
- Testing strategies

## Quick Reference

### Query Patterns

**Simple Query**

```typescript
// Prisma
const user = await this.prisma.user.findUnique({ where: { tenantId, id } });

// Objection
const knex = await this.tenantDb.getTenantKnex(tenantId);
const user = await User.query(knex).findById(id);
```

**Query with Relations**

```typescript
// Prisma
const user = await this.prisma.user.findUnique({
  where: { tenantId, id },
  include: { roles: { include: { permissions: true } } },
});

// Objection
const user = await User.query(knex)
  .findById(id)
  .withGraphFetched("roles.permissions");
```

**Create**

```typescript
// Prisma
const user = await this.prisma.user.create({ data: { ... } });

// Objection
const user = await User.query(knex).insert({ ... });
```

**Update**

```typescript
// Prisma
const user = await this.prisma.user.update({ where: { id }, data: { ... } });

// Objection
const user = await User.query(knex).patchAndFetchById(id, { ... });
```

**Delete**

```typescript
// Prisma
await this.prisma.user.delete({ where: { id } });

// Objection
await User.query(knex).deleteById(id);
```

## Resources

- [Knex.js Documentation](https://knexjs.org)
- [Objection.js Documentation](https://vincit.github.io/objection.js)
- [MULTI_TENANT_IMPLEMENTATION.md](./MULTI_TENANT_IMPLEMENTATION.md) - Full implementation details