Support injecting providers into dataSourceFactory

[brandon-leapyear]

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

I would like to provide my own DataSource, but I need to inject my ConfigService so that I can do things in my DataSource depending on configuration.

Describe the solution you'd like

The most straightforward solution is to provide a dataSourceFactoryInject option.

A bigger change (which I think makes more sense) would be to remove dataSourceFactory and add

dataSourceProviderModify: (provider) => provider
entityManagerProviderModify: (provider) => provider

which passes in the default provider, and the user can modify whatever they want, e.g.

dataSourceProviderModify: (provider) => ({
  ...provider,
  useFactory: (typeOrmOptions, configService) => {
    return new MyDataSource(typeOrmOptions, configService)
  },
  inject: [...provider.inject, ConfigService],
})

Teachability, documentation, adoption, migration strategy

See solution.

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

See problem.

[khanh-le-otsv]

I would like to suggest this feature as well.

[tafaust]

I need this feature as well. My current workaround (not an actual workaround) is to

const configService = new ConfigService();
// use the configService in DataSource creation

Moreover, if one uses the dataSourceFactory callback of type TypeOrmDataSourceFactory = (options?: DataSourceOptions) => Promise<DataSource>; there is the chance to create the DataSourceOptions here from the provided ConfigService in case of undefined.

Here is an example of a dataSourceFactory implementation outlining why this feature is urgently needed:

export const dataSourceFactory: TypeOrmDataSourceFactory = async (
  options?: DataSourceOptions,
) => {
  const configService = new ConfigService();

  return new DataSource(options ?? {
    type: 'mysql',
    host: configService.get('HOST'),
    port: +configService.get('PORT'),
    username: configService.get('USERNAME'),
    password: configService.get('PASSWORD'),
    database: configService.get('DATABASE'),
    // and so on ...
  }).initialize();
};

But we could also use provider to enhance DataSource creation in other ways. I create a pg-mem connection for instance when serving or unit testing my backends locally.