[hibernate-dev] Mapping JPA's @MapKeyEnumerated and @Enumerated on native-enum supporting datastores

[Sanne Grinovero]

On 26 August 2016 at 10:34, Gunnar Morling <gunnar at hibernate.org> wrote:
> How about having a custom @Enumerated annotation which offers NATIVE as an
> additional choice?

I guess we could, but it's sad that we'd still have to default to the
"wrong" mapping,
at least for all those people who won't read all of our docs.

Would that live in OGM or ORM ?

>
> 2016-08-26 10:16 GMT+02:00 Emmanuel Bernard <emmanuel at hibernate.org>:
>>
>> Can you give HotRod's example of native enum - I imagine Protobuf ?

>From the OGM testsuite:

@Entity
public class Bookmark {

public enum Classifier {
HOME, WORK
}

@Id
private String id;
@Enumerated(EnumType.STRING)
private Classifier classifier;
[...]
}

Is mapped as:

  message Bookmark {
    required string id = 1;
    optional string classifier = 2;
  [...]

(correctly as it's explicitly requesting a STRING EnumType)

A more "native" Protobuf mapping would look like:

  enum Classifier {
    HOME = 0;
    WORK = 1;
  }

  message Bookmark {
    required string id = 1;
    optional Classifier classifier = 2;
  [...]

I had already implemented this, just realising later that there's no
way to enable this better looking mapping.

>>
>> The issue I see is that ordinal could be an acceptable explicit decision
>> that would not be available to the user if you use default as native.
>>
>> I'm tempted to go native all the time at the detriment of people that
>> need high customization.

I'd be tempted too as the second mapping looks much more natural,
however this would break things for people who need it to be an
integer, e.g. if they have other clients who expect an int.
On the other hand, the "I need compatibility with another client"
argument is quite weak, as at this stage the Hot Rod Dialect generates
its own schema and pretty much mandates using the one it generates.

Proposal: I have it mapped as "native enums" by default, and give a
global configuration property to honour the annotations instead? This
would be a global setting though, so if one wants one attribute
"native encoded" and another "int encoded" that wouldn't be possible.

Thanks,
Sanne

>>
>> Emmanuel
>>
>> On Mon 2016-08-15 18:14, Sanne Grinovero wrote:
>> > In the context of Hibernate OGM, it turns out that some datastores
>> > have a rather nice "native" support for enums.
>> >
>> > We aim to map each property of the user's domain model to its most
>> > appropriate "physical type", unless the choice is overriden by the an
>> > explicit user request.
>> >
>> > In the case of an Enum, JPA annotations such as @Enumerated have an
>> > attribute EnumType to choose the physical representation:
>> >
>> > public enum EnumType {
>> >     /** Persist enumerated type property or field as an integer. */
>> >     ORDINAL,
>> >
>> >     /** Persist enumerated type property or field as a string. */
>> >     STRING
>> > }
>> >
>> > However, there's no support for a "NATIVE". Also, the annotation
>> > specifies that "ORDINAL" is the default value so I can't just assume
>> > that the user didn't specify anything and we're good to use our own
>> > NATIVE implementation.
>> >
>> > Assuming that we can't change the JPA spec, any suggestion on when I
>> > could have the Hot Rod dialect for OGM to actually produce a "nice"
>> > mapping into native enums?
>> >
>> > I'm tempted to just use natives all the time; In the case in which the
>> > user opted for "STRING" I could drop a warning - or decide to honour
>> > that - but in case of ORDINAL I just can't tell if it's a default
>> > choice or not so I think a warning would be too much.
>> >
>> > Another alternative would be that I "go native" when the @Enumerated
>> > annotation isn't specified at all: looks like this mapping is valid
>> > according to ORM as it seems to treat it as if there was an implicit
>> > @Enumerated annotation; I'm not happy about having to rely on people
>> > to not use an explicit annotation though.
>> >
>> > Thanks,
>> > Sanne
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