7.1.x Fix Enum JSON/XML Serialization for Round-Trip Compatibility

[codeconsole]

The Problem

Grails had asymmetric enum handling that broke round-trips:

POST/PUT (What you send):

{"stage":"SUBMIT"}

GET (What you received back):

{"stage":{"enumType":"com.example.ChallengeStage","name":"SUBMIT"}}

Result: You couldn't POST back what you GET!

The Fix

Enums now serialize the same way they deserialize - as simple strings:

POST/PUT (What you send):

{"stage":"SUBMIT"}

GET (What you get back):

{"stage":"SUBMIT"}

Result: What you POST is what you GET.

Technical Changes

• JSON.java: Handle enums as primitives (like strings, numbers, booleans)
• XML.java: Handle enums as primitives (like strings, numbers, booleans)
• Removed dead code: EnumMarshaller classes (no longer needed)
• Updated tests: Verify symmetric serialization/deserialization

[jdaugherty]

You are asking to merge this into 7.0.x, but this is on the 7.1.x code line?

[codeconsole]

7.1.x

[jdaugherty]

So this is one of the first things I do in a Grails app. I 100% agree it needs fixed, but unfortunately this is a breaking change since we're registering the marshaller by default. Our support policy says we won't break except on major releases. I think to accept this change in 7.x, we have to not register these by default & then in 8.x we can register them by default.

[codeconsole]

So this is one of the first things I do in a Grails app. I 100% agree it needs fixed, but unfortunately this is a breaking change since we're registering the marshaller by default. Our support policy says we won't break except on major releases. I think to accept this change in 7.x, we have to not register these by default & then in 8.x we can register them by default.

@jdaugherty I am not registering anything. I am deleting the marshallers which could be added back in by someone if they really wanted them.

[matrei]

As this could break someones parsing of data returned from an endpoint, we could keep backwards compatibility by defaulting to the old behavior and add a feature flag to enable the new behavior in 7.1 and then replace and remove the old behavior in 8.

[codeconsole]

As this could break someones parsing of data returned from an endpoint, we could keep backwards compatibility by defaulting to the old behavior and add a feature flag to enable the new behavior in 7.1 and then replace and remove the old behavior in 8.

@matrei I think 8 is too far off for something that IMO is completely broken. Does this POST request work?

curl -X POST 'https://localhost:8080/test' \
  -H 'Content-Type: application/json' \
  -d '{"stage":{"enumType":"com.example.ChallengeStage","name":"SUBMIT"}}'

if the answer is no, then this is clearly a bug and needs to be fixed.

There is a reason why you have to submit json like this:

curl -X POST 'https://localhost:8080/test' \
  -H 'Content-Type: application/json' \
  -d '{"stage":"SUBMIT"}'

even form submission sends enum String values

curl -X POST 'https://localhost:8080/test'\
  -H 'Content-Type: application/x-www-form-urlencoded' \
  --data 'stage=SUBMIT'

[matrei]

I think 8 is too far off

With a feature flag, the new serialization format would be available in 7.1.

something that IMO is completely broken

I don't think it's broken, it just does not work like you would like.
And I agree with you.

But it is a breaking change, and we should avoid that in a minor version update.

[jdaugherty]

I'm in agreement with @matrei . I originally looked at this and assumed we were registering new marshallers, but my point was that we can't break behavior - even bad behavior in a point release. We've stated we would only do it in a major release.

Everyone seems to agree this is really bad behavior though. I'm willing to discuss in the weekly and if there is consensus we can deviate from our policy.

[codeconsole]

Well the trade off is doing it with a marshaller or not. Marshaller seems overkill.

grails-core/grails-converters/src/main/groovy/grails/converters/JSON.java

Lines 179 to 197 in c899909

	if (o == null) {
	writer.valueNull();
	}
	else if (o instanceof CharSequence) {
	writer.value(o);
	}
	else if (o instanceof Class<?>) {
	writer.value(((Class<?>) o).getName());
	}
	else if (o instanceof Enum) {
	writer.value(((Enum<?>) o).name());
	}
	else if (o instanceof Number) {
	writer.value((Number) o);
	} else if (o instanceof Boolean) {
	writer.value((Boolean) o);
	} else if (o.getClass().isPrimitive() && !o.getClass().equals(byte[].class)) {
	writer.value(o);
	}

@matrei define feature flag. A config setting in application.yml?

[matrei]

define feature flag. A config setting in application.yml?

@codeconsole Yes, a config value. However it is set.

[codeconsole]

merged in 7.0.x #15212

[sbglasius]

@codeconsole Good work!