Remove special handling of Arrays

[schauder]

Instead of using special code paths for the handling of arrays these should be handled by converters.

The same #992 to did for AggregateReference

[mp911de]

To some extent, #1593 has fixed the issue regarding collections and arrays. Converters are expected to handle individual values hence the JdbcConverter (and its R2DBC variant) are expected to iterate over all collection values and apply conversion.

[denniseffing]

@schauder Is it possible that using Converters to convert individual collection values is broken?

The derived column type of every collection-like property that is not an entity is the Array class: spring-projects/spring-data-relational@3117465d:spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/convert/MappingJdbcConverter.java#180

When a collection is written, every value of it is mapped and stored in an ArrayList (as expected), however, the code then checks if the mapped ArrayList is an instance of the derived column type (i.e. Array) before returning it, which can never be true.
spring-projects/spring-data-relational@3117465d:spring-data-relational/src/main/java/org/springframework/data/relational/core/conversion/MappingRelationalConverter.java#770

This effectively means that it is impossible to save an entity that looks like this:

class SomeEntity {
    // ... id, persistence creator etc.
   
    List<CustomType> types;
}

record CustomType(String value) { }

class CustomTypeToStringConverter implements Converter<CustomType, String> {

	@Override
	public String convert(CustomType source) {
		return source.value;
	}
}

class StringToCustomTypeConverter implements Converter<String, CustomType> {

	@Override
	public Region convert(String source) {
		return new CustomType(source);
	}
}

The only way to make this work is to create another wrapper type like this:

record CustomTypes(List<CustomType> types) {}

// converters for CustomTypes

Am I missing something here or is this really just not working as I would have expected it to?

[schauder]

It is perfectly possible that this is broken. Please create a separate ticket for that.

[schauder]

Closing this, because we decided to go the opposite direction and have dedicated code for Arrays, AggregateReference and similar.