Create a multi-tenant application in Nest.js Part 3 (multi-database setup)
Tags: node, typescript, database, microservices
Published: 2021-11-13 14:11:35

In [part 1](https://dev.to/ismaeil_shajar/create-a-multi-tenancy-application-in-nestjs-part-1-microservices-setup-59cm), we set up the nestjs framework and configured and tested microservices architecture application using nest.js. In [part 2](https://dev.to/ismaeil_shajar/create-a-multi-tenancy-application-in-nestjs-part-2-database-setup-23ee), we used Sequelize and mongoose to access the database and tested for both MySQL database and MongoDB.

## Async Connection
In this part; we will see how to let the application connect to multiple databases depending on the request. Since it is a multi-tenancy application, each tenant has their own database containing their data accessing the same application, thus the application needs to connect to different databases.
We will change the pass repository option method and use `forRootAsync()` instead of `forRoot()`, we need to use a custom class for configuration.

For both sequelize and mongoose, add this: 
```js
MongooseModule.forRootAsync({
    useClass:MongooseConfigService
  }),
SequelizeModule.forRootAsync({
      useClass:SequelizeConfigService
})
```
We will create a config file and two classes: `MongooseConfigService` and `SequelizeConfigService` 
>The plan here is to add injection for each incoming request and use a domain to switch between connections.
>
> So we need to use `@Injectable({scope:Scope.REQUEST})`, and on the class constructor we use `@Inject(REQUEST) private read-only request` so we can get host information from request data.
> 
> For example let say the domain is example.com, and we have a tenant called `company1`, then the domain will be company1.example.com. Same thing for `company2` tenant, the domain will be company2.example.com and so on.


> config/MongooseConfigService.ts

```ts
import { Inject, Injectable, Scope } from "@nestjs/common";
import { REQUEST } from "@nestjs/core";
import { MongooseModuleOptions, MongooseOptionsFactory } from "@nestjs/mongoose";

@Injectable({scope:Scope.REQUEST})
export class MongooseConfigService implements MongooseOptionsFactory {
    constructor(@Inject(REQUEST) private readonly request,){}

  createMongooseOptions(): MongooseModuleOptions {
    let domain:string[]
    let database='database_development'
    if(this.request.data ){
      domain=this.request.data['host'].split('.')
      console.log(this.request)
    }
    else{
      domain=this.request['headers']['host'].split('.')
    }

    console.log(domain)
    if(domain[0]!='127' && domain[0]!='www' && domain.length >2){
      database='tenant_'+domain[0]
      console.log('current DB',database)
    }
    return {
      uri: 'mongodb://localhost:27017/'+database,
    };
  }
}
```
> config/SequelizeConfigService.ts

```ts
import { Inject, Injectable, Scope } from "@nestjs/common";
import { REQUEST } from "@nestjs/core";
import { CONTEXT, RedisContext, RequestContext } from "@nestjs/microservices";
import { SequelizeModuleOptions, SequelizeOptionsFactory} from "@nestjs/sequelize";

@Injectable({scope:Scope.REQUEST})
export class SequelizeConfigService implements SequelizeOptionsFactory {
    constructor(@Inject(REQUEST) private readonly request:RequestContext){}
    
    createSequelizeOptions(): SequelizeModuleOptions {

      let domain:string[]
      let database='database_development'
      if(this.request.data ){
        domain=this.request.data['host'].split('.')
        console.log(this.request)
      }
      else{
        domain=this.request['headers']['host'].split('.')
      }

      console.log(domain)
      if(domain[0]!='127' && domain[0]!='www' && domain.length >2){
        database='tenant_'+domain[0]
        console.log('current DB',database)
      }

    return {
      dialect: 'mysql',
      host: 'localhost',
      port: 3306,
      username: 'ismaeil',
      password: 'root',
      database: database,
      autoLoadModels: true,
      synchronize: true,
    };
  }
}
```

## Performance -- Production
in production we need to avoid create connection in every request so we will do some edits in user module and services.

### Solution:
Our problem here is connection was create every request and this connection not close and also I don't reuse.
So we can use even close connection or use existing connection in new request or use both and manage when create and when close.


#### Closing connection
To close connection first wen need to access it.by naming connections we can access connection using @InjectConnection then in service we can close conection every time after finish . 
So we need this edits
> in user-service.module.ts

```ts

     SequelizeModule.forRootAsync({
      name: 'development',
       useClass:SequelizeConfigService
     }),
     SequelizeModule.forFeature([Users], 'development')], // use connection name in forFeature
```
> and in user-service.service.ts

```ts
export class UserServiceService {
  constructor(
    @InjectConnection('development') private readonly sequelize: Sequelize, // access connection by name 'development'
    @InjectModel(Users, 'development')
  private readonly userModel: typeof Users){}
  async findAll() {
    let result =await this.userModel.findAll()
    this.sequelize.close() // after  every use will close connection
    return result;
  }
  /// the rest 
}
```

#### Use existing connection
In order to prevent the creation of SequelizeConfigService inside SequelizeModule and use a provider imported from a different module, you can use the useExisting syntax.

and we need to create external module that provide sequelize configuration .
> create new file named user-config.module.ts
```ts

@Module({
  providers: [SequelizeConfigService],
  exports:[SequelizeConfigService]
})

export class UserConfigModule {}
```
> then edit user-service.module.ts

```ts
  SequelizeModule.forRootAsync({
    imports:[UserConfigModule],
    useExisting: SequelizeConfigService,
  }),
```

### Use both
if we add ability to use both ways code will be like this 
> user-service.module.ts
```ts
@Module({
   imports: [
  SequelizeModule.forRootAsync({
    imports:[UserConfigModule],
    name: 'development',
    useExisting: SequelizeConfigService,
  }),
    SequelizeModule.forFeature([Users], 'development')],
  controllers: [UserServiceController],
  providers: [UserServiceService],
})

export class UserServiceModule {}
```

> user-service.service.ts

```ts
@Injectable()
export class UserServiceService {
  constructor(@InjectConnection('development') private readonly sequelize: Sequelize,
    @InjectModel(Users, 'development')
  private readonly userModel: typeof Users){}
  async findAll() {
    let result =await this.userModel.findAll()
    //console.log(this.sequelize.close())  // optional or you can manage it 
    return result;
  }
  
  async create( createUserDto:CreateUserDto):Promise<Users> {
    return this.userModel.create(<Users>createUserDto)
    
  }
}
```

and we have new module 
> user-config.module.ts

```ts
import { Module } from '@nestjs/common';
import { SequelizeConfigService } from './sequelize-config-service';

@Module({
  providers: [SequelizeConfigService],
  exports:[SequelizeConfigService]
})

export class UserConfigModule {}
```

## Testing
After finishing the configuration, we need to do some work to test it because we need to map our localhost and IP to a domain.
I will try to use two ways to test the application locally but for the production, it will be a configuration in your domain provider.
### 1- Edit the hosts file in your local machine and edit this file every time you add a tenant
Go to the following file in Linux: `/etc/hosts` and in windows: `c:\windows\system32\drivers\etc\hosts`  and add
``` sh
## lines
127.0.0.1	example.com
127.0.0.1	company1.example.com
127.0.0.1	company2.example.com
```
### 2- Use local dns
In linux you can install dnsmasq and follow these steps
> 1- Install dnsmasq in NetworkManager.
> 
> 2- Add the configuration file `sudo nano /etc/NetworkManager/dnsmasq.d/dnsmasq-localhost.conf`.
> 
> add this line in the file:
```
address=/.example.com/127.0.0.1
```
> 3- Restart the service `sudo systemctl reload NetworkManager`.


Source code available in  [git](https://github.com/ismaeil-shajar/multitenancy) branch multi-database

Next in part 4 we will add a security level and user roles.