Whether a connection error handling method can be added

[jiayisheji]

Is there an existing issue that is already proposing this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe it

[Nest] 6788  - 2022/02/11 pm5:53:31   ERROR [MongooseModule] Unable to connect to the database. Retrying (1)...
[Nest] 6788  - 2022/02/11 pm5:53:34   ERROR [MongooseModule] Unable to connect to the database. Retrying (2)...
[Nest] 6788  - 2022/02/11 pm5:53:37   ERROR [MongooseModule] Unable to connect to the database. Retrying (3)...
[Nest] 6788  - 2022/02/11 pm5:53:40   ERROR [MongooseModule] Unable to connect to the database. Retrying (4)...
[Nest] 6788  - 2022/02/11 pm5:53:43   ERROR [MongooseModule] Unable to connect to the database. Retrying (5)...
[Nest] 6788  - 2022/02/11 pm5:53:46   ERROR [MongooseModule] Unable to connect to the database. Retrying (6)...
[Nest] 6788  - 2022/02/11 pm5:53:49   ERROR [MongooseModule] Unable to connect to the database. Retrying (7)...
[Nest] 6788  - 2022/02/11 pm5:53:52   ERROR [MongooseModule] Unable to connect to the database. Retrying (8)...
[Nest] 6788  - 2022/02/11 pm5:53:55   ERROR [MongooseModule] Unable to connect to the database. Retrying (9)...
[Nest] 6788  - 2022/02/11 pm5:53:55   ERROR [ExceptionHandler] Invalid scheme, expected connection string to start with "mongodb://" or "mongodb+srv://"

Connection Error Failed to catch Error information.
Connection Error causes the connectionFactory method to not work.

Error handling is facilitated if a method is provided that can catch connection errors.

Describe the solution you'd like

https://github.com/nestjs/mongoose/blob/master/lib/mongoose-core.module.ts#L80

const {catchError} = require("rxjs/operators");

@Global()
@Module({})
export class MongooseCoreModule implements OnApplicationShutdown {
....
    const connectionProvider = {
      provide: mongooseConnectionName,
      useFactory: async (
        mongooseModuleOptions: MongooseModuleOptions,
      ): Promise<any> => {
        const {
          retryAttempts,
          retryDelay,
          connectionName,
          uri,
          connectionFactory,
         connectionError,
          ...mongooseOptions
        } = mongooseModuleOptions;

        const mongooseConnectionFactory =
          connectionFactory || ((connection) => connection);
        
       const mongooseConnectionError =
          connectionError || ((error) => {});
      
        return await lastValueFrom(
          defer(async () =>
            mongooseConnectionFactory(
              await mongoose
                .createConnection(
                  mongooseModuleOptions.uri as string,
                  mongooseOptions,
                )
                .asPromise(),
              mongooseConnectionName,
            ),
          ).pipe(
            handleRetry(
              mongooseModuleOptions.retryAttempts,
              mongooseModuleOptions.retryDelay,
            ),
            catchError(err => {
                  mongooseConnectionError(err);
                  throw error;
            })
          ),
        );
      },
      inject: [MONGOOSE_MODULE_OPTIONS],
    };
    .....
}

Just throw the error through the RXJS catchError.

Teachability, documentation, adoption, migration strategy

The connectionError method is used to capture connectionError information and report exceptions.

MongooseModule.forRootAsync({
    imports: [ConfigModule],
    useFactory: async (configService: ConfigService) => {
      return {
        uri: 'mongodb://localhost/test',
        connectionError: (error) => {
          console.log('MongooseModule connectionError', error);
          // Report connection error messages by email
        },
      };
    },
    inject: [ConfigService],
}),

What is the motivation / use case for changing the behavior?

Currently, if the connection fails, the error cannot be caught and a remedy policy implemented.

The connectionFactory method is not executed after a connection error.

[kamilmysliwiec]

Would you like to create a PR for this issue?

[jiayisheji]

@kamilmysliwiec ok

[morelikeahumanraghu]

Trying to know why the connection with Mongodb was failing -- guessing this PR should give the stack trace.

[kblestarge]

I would like to gracefully fail by catching and logging the thrown error from a connection problem, but not breaking the app. Would this proposed solution work for my use-case?
What is the status of your PR, @jiayisheji?

[CodyTseng]

@jiayisheji If you're busy, I'd be happy to implement this PR.

[kamilmysliwiec]

Let's track this here #1550