#301 Make SQL generators extensible so that custom generators could be plugged in without Pramen recompilation

[yruslan]

Closes #301

The PR adds the ability to use custom JDBC drivers with custom SQL generators without recompiling Pramen. You can also use custom SQL generators with JDBC drivers that are already supported by Pramen, if there is a reason to do that.

Example JDBC reader config:

sources = [
  {
    name = "jdbc"
    factory.class = "za.co.absa.pramen.core.source.JdbcSource"

    jdbc {
      driver = "com.example.Jdbc.Driver"
      connection.string = "$url"
      user = "$user"
      password = "$password"
    }

    has.information.date.column = true
   
    information.date.column = "INFO_DATE"
    information.date.type = "date"
    information.date.app.format = "YYYY-MM-dd"

    # Specify the custom generator for the custom JDBC driver
    sql.generator.class = "com.example.CustomSqlGeneratorClass"
  }
]

[github-actions]

Unit Test Coverage

File	Coverage [94.92%]	🍏
TableReaderJdbcConfig.scala	100%	🍏
CsvUtils.scala	100%	🍏
SqlGeneratorHive.scala	96.97%	🍏
SqlGeneratorOracle.scala	96.94%	🍏
SqlGeneratorPostgreSQL.scala	96.84%	🍏
SqlGeneratorDb2.scala	96.84%	🍏
SqlGeneratorGeneric.scala	96.84%	🍏
SqlGeneratorHsqlDb.scala	96.84%	🍏
SqlGeneratorDenodo.scala	96.78%	🍏
SqlGeneratorMicrosoft.scala	95.53%	🍏
SqlGeneratorSas.scala	94.08%	🍏
SqlGeneratorLoader.scala	92.49%	🍏
TableReaderJdbc.scala	87.91%	🍏

Total Project Coverage	83.48%	🍏

[kevinwallimann]

You may consider using ??? instead of null to avoid the usage of nulls in Scala.

[yruslan]

Interesting idea. I always use null in dummy classes, coming from Uncle Bob mocking principles. And I use ??? when something not implemented yet, but I need the project to compile.

The difference for me is:

• When ??? is returned it means the method implementation is unfinished, and no ??? should be in PRs.
• When null is returned it means it is a dummy class and the implementation of this method is never intended.

Let me know if given this, you still prefer ???.

[kevinwallimann]

Did you leave the methods fromDriverName and fromClass with public access on purpose?

[yruslan]

I see, it indeed makes sense to make the private since the object has getSqlGenerator() method that can be used in both cases.