API to return primitive Java value types

[mp911de]

Feature Request

Is your feature request related to a problem? Please describe

When using R2DBC drivers in the context of a object-mapping framework, it's desirable to distinguish between simple types (R2DBC/driver primitives) and complex types (user-types).

Right now, R2DBC defines a set of primitives (Java primitives, several JSR-310 types). Additionally, each driver may define its own primitive types (e.g. Postgres with Json and Geo types, MySQL with BitSet and java.time.Year, SQL Server with BigDecimal/BigInteger, PostGIS with additional Geo types, and so on).

While the majority of used types map to R2DBC spec types that can be generally considered simple types, driver-specific types require maintenance by object-mapping library maintainers to catch up with what happens in the driver space.

Describe the solution you'd like

Ideally, R2DBC drivers report their supported simple types that can be natively interchanged with the database through some sort of API.

The type system of several databases can be dynamic which requires interaction with the database to determine the effective typeset. In most cases, integrations are configured with a ConnectionFactory that holds the configuration. Once configured, a ConnectionFactory typically does not change its config which could make it a source for type details. With the assumption of ConnectionFactoryMetadata being not tied to database interaction, ConnectionFactory doesn't seems a good fit, though.

Connection already exposes ConnectionMetadata that may contain details retrieved from the actual database connection. We could extend ConnectionMetadata with a default method that does not break implementations:

An interface along the lines of the following example could serve the purpose:

public interface ConnectionMetadata {

    String getDatabaseProductName();
    String getDatabaseVersion();
    
    /**
     * Returns a collection of types that are natively supported by the driver to represent database values.
     */
    Collection<Class<?>> getNativeTypes(); // getSimpleTypes(), getValueTypes()
}

The actual method name to be discussed.

Describe alternatives you've considered

Manual registration in the object mapping framework. This is a tedious effort to keep up with driver changes.

Teachability, Documentation, Adoption, Migration Strategy

Update the specification with the interface definition.