Multiple data sources: allow renaming default data source (feature request)

[karaken12]

When using multiple data sources, there must be a default data source and it must be called 'dataSource'. In a project using several data sources, "dataSource" is not a useful semantic name. As a developer, I would like to be able to rename the default data source.

I would expect this to be a configuration parameter. There is already a GORM syntax for referring to the default data source, so I would expect that to continue to work. I would also expect an incorrectly configured system to produce an intelligible error message (see #10144 for an example of the current stack trace).

Example configuration syntax

dataSources:
    default: sourceTwo
    sourceOne:
        driverClassName: org.h2.Driver
        ...
    sourceTwo:
        driverClassName: org.h2.Driver
        ...
    sourceThree:
        driverClassName: org.h2.Driver
        ...

[MichaelMorett]

This would be very useful. Perfect use case of why this is necessary:

1. Plugin GRAILS-10580 Rollback of transaction with checked exception grails-data-mapping#1 uses default dataSource, and also uses Database Migration Plugin.

2. App GRAILS-10580 Rollback of transaction with checked exception grails-data-mapping#1 uses plugin GRAILS-10580 Rollback of transaction with checked exception grails-data-mapping#1.

3. App Manually merge changes for GRAILS-9644 grails-data-mapping#2 uses Plugin GRAILS-10580 Rollback of transaction with checked exception grails-data-mapping#1, but also has separate domain objects, and also uses Database Migration Plugin to track changes to those domain classes.

Attempts to track domain/database changes with Database Migration Plugin from App apache/grails-data-mapping#2 are impossible (unless someone can provide sample syntax to use). It will do a diff on "dataSource", which is coming from Plugin apache/grails-data-mapping#1. (I'm already tracking changes to domain objects in Plugin apache/grails-data-mapping#1 by Database Migration Plugin used in Plugin apache/grails-data-mapping#1 and do not want to do this.)

The Database Migration plugin has options to use different dataSources -- perfect for this use case -- however, Grails won't let you name the default dataSource, thereby defeating this option when using it from App apache/grails-data-mapping#2.

There is an implicit assumption that multiple dataSources would only be used from within a single app/plugin. The design didn't foresee or account for multiple dataSources spread over multiple apps/plugins, working together as a unit.

Being an opinionated framework is great, but in this case, there is no way to override a default.

[jameskleeh]

@MichaelMorett Couldn't the above be solved by simply never using the default datasource in a plugin?