Add API for property specific converters [DATACMNS-1036]

[spring-projects-issues]

Oliver Drotbohm opened DATACMNS-1036 and commented

The current conversion subsystem can only deal with type based converters. We should add API to allow users to register converters for a specific PersistentProperty

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Issue Links:

• DATACASS-668 Provide a way to custom convert some properties of an entity
  ("is depended on by")

• DATAJDBC-379 Disable auto-apply custom converts
  ("is depended on by")

• DATAJDBC-450 Storing non root entities in serialized form

• DATAMONGO-889 Missing field and property annotations do not allow conditional conversion

5 votes, 5 watchers

[spring-projects-issues]

Oliver Drotbohm commented

• ConversionContext
  • EntityConverter
  • MappingContext
  • Owner
• PersistentPropertyConverter<T, S, P extends PersistentProperty<P>>
  • S write(T value, P property, ConversionContext context);
  • T read(S value, P property, ConversionContext context);
• Open questions:
  • How to register those PPConverters? As a user? As another framework (Spring Security)?

interface PPC<T, S, P extends PersistentProperty<P>> { …}

interface PPCPlugin extends Plugin<P> { … }

class Conversions implements PPCPlugin {

	PropertyPath path;

	<K, L extends S> PPCSupport assignTo(PPC converter, Class<K> type, Function<K, L> consumer) {
		Recorder recorder = MIR.forProxyOfType(type).record(consumer);
		this.path = PropertyPath.of(type, recorder.getPropertyPath());
	}
	

	supports(PP property) {

		if (path.getSegment() != null) {
			path.getOwner == property.getOwner
			path.getSegment == property.getName;
		} else {
			path.getOwner = property.getType
		}
	}
}


PluginRegistry<PPC<…>, PersistentProperty<?>> registry;

PPC converter = registry.getPluginFor(property, () -> new DefaultPPC());


class MyEncodingConverter extends PPCSupport<String, String, …> {

	read(…);

	write(…);
}

class Config {

  @Bean
  Conversions foo() {

    return ConversionsBuilder.forConverter(new MyEncodingConverter())
      .assignByProperty(Employee.class, Employee::getPassword, e -> e.getEmail().getValue())
      .assingByType(Password.class));
    }
  }
}

[nbali]

If I might have a suggestion, the converter would be superior even to the JPA version if the context (the POJO being converted, the field being converted, etc) would be also available and not just the values.

JPA (only values):
https://docs.oracle.com/javaee/7/api/javax/persistence/AttributeConverter.html
vs
Objectify (with context):
https://github.com/objectify/objectify/blob/master/src/main/java/com/googlecode/objectify/impl/translate/TranslatorFactory.java
https://github.com/objectify/objectify/blob/master/src/main/java/com/googlecode/objectify/impl/translate/Translator.java

For example the second can be used to check for annotations on the field (or values of other fields), and the conversion can be dynamic based on that.

@RequiredArgsConstructor
class EncryptingTranslatorFactory implements TranslatorFactory<String, String> {

    @NonNull
    private final EncryptionService encryptionService;

    @Override
    public Translator<String, String> create(TypeKey<String> tk, CreateContext ctx, Path path) {
        if (tk.isAnnotationPresent(Sensitive.class)) {
            if (tk.getTypeAsClass() != String.class) {
                throw new IllegalStateException("@Sensitive is only supported for String at the moment!");
            }
            return <...>;
        } else {
            return null;
        }
    }

}