Restructuring Database.Connection to allow for database specific types.

[jdunkerley]

Pull Request Description

• Added databases, database, set_database.
• Added schemas, schema, set_schema.
• Added table_types,
• Added tables.
• Moved the vast majority of the connection work into a lower level JDBC_Connection object.
• Connection represents the standard API for database connections and provides a base JDBC implementation.
  • SQLite_Connection has the Connection API but with custom databases and schemas methods for SQLite.
  • Postgres_Connection has the Connection API but with custom set_database, databases, set_schema and schemas methods for Postgres.
• Updated Redshift - no public API change.

Checklist

• Note: the Redshift connection does not pass the Redshift tests at the moment.
  • This is not introduced by this PR but was already the case.
  • Column names are returned in lower case.
  • Order of results is not stable.

Please include the following checklist in your PR:

• The documentation has been updated if necessary.
• All code conforms to the
  Scala,
  Java,
  and
  Rust
  style guides.
• All code has been tested:
  • Unit tests have been written where possible.
  • If GUI codebase was changed: Enso GUI was tested when built using BOTH
    ./run ide dist and ./run ide watch.

[radeusgd]

Having both properties database and databases seems slightly confusing to me - when I would look at the code I wouldn't be sure what is exactly the difference between the two. I may guess correctly, and also documentation should make it clear. But maybe we could rename database to something like current_database? Then it would be clear that this is the currently selected one and databases are all available ones.

The same applies for schema and schemas.

[jdunkerley]

Having both properties database and databases seems slightly confusing to me - when I would look at the code I wouldn't be sure what is exactly the difference between the two. I may guess correctly, and also documentation should make it clear. But maybe we could rename database to something like current_database? Then it would be clear that this is the currently selected one and databases are all available ones.

The same applies for schema and schemas.

The database/databases and schema/schemas was discussed with Ned and Wojciech in Gdansk. It was felt it was clear and fairly simple but we could rename if it doesn't feel that way within the UI experience.

[JaroslavTulach]

SQLite_Connection implements the Connection for SQLite overriding databases and schemas

I am curious to know what that is sentence supposed to mean? I see SQLite_Connection, but it doesn't extend Connection. I don't even know how are they related? Where does the "implements" happen?

Is the list of supported DB types hardcoded currently? How can one connect to SQLite and how can one connect to Postgres?

Is there a way to expand the list of supported DB now? In the future? Where I would add support of such a DB?

[jdunkerley]

SQLite_Connection implements the Connection for SQLite overriding databases and schemas

I will re-word it. The specific connection types are supposed to implement the same API as the Connection type. We have no way to do inheritance (either as an interface or a derived type). The idea is all specific implementations will share the API and can use the basic implementation in Connection if they don't need any custom behaviour.

Is the list of supported DB types hardcoded currently? How can one connect to SQLite, and how can one connect to Postgres?

Is there a way to expand the list of supported DB now? In the future? Where I would add support of such a DB?

Currently, the supported databases are SQLite, Postgres and Redshift. They will be presented as a union type on the Database.connect method. It is envisaged that a modular expansion approach will be added in future. Currently (and for v1), adding a new database such as SQL Server would involve expanding the Standard.Database library with the required types.

[radeusgd]

Looks good to me, just a few small suggestions.