Enhancement - Add an option to use a JSON document as the source model in the Playground

[viht0ri]

It would be nice to allow transformations from JSON documents to models in the playground. While the backend already supports receiving a JSON document under the json field of the request payload, the frontend code path always populates the flexmi and emfatic fields.

epsilon-website/playground/js/Playground.js

Lines 248 to 262 in b5e9808

	function editorsToJsonObject() {
	return {
	"language": language,
	"outputType": outputType,
	"outputLanguage": outputLanguage,
	"program": programPanel.getValue(),
	"secondProgram": secondProgramPanel.getValue(),
	"emfatic": firstMetamodelPanel.getValue(),
	"flexmi": firstModelPanel.getValue(),
	"secondEmfatic": secondMetamodelPanel.getValue(),
	"secondFlexmi": secondModelPanel.getValue(),
	"thirdEmfatic": thirdMetamodelPanel.getValue(),
	"thirdFlexmi": thirdModelPanel.getValue()
	};
	}

[kolovos]

Flexmi supports a YAML flavour so, as YAML is a superset of JSON, it's already possible to type JSON into the models panels of the playground. Is this sufficient for your use-case or were you thinking of adding support for Epsilon's plain JSON driver to the playground?

[viht0ri]

Thanks for a quick reply! My current use-case is working with schemaless JSON as the source model. I have used the plain JSON driver in Eclipse Epsilon locally, and my rules are generally of the form:

rule DataFlows
	transform j : Source!JSONObject
	to flow : Target!ElementX {
	guard : j.type == "elementx"
        ...
        }

I don't have much experience with the YAML flavour, or Epsilon in general, but my current understanding is that I would need to define some sort of schema unless there are analogues to JSONObject and JSONArray that can be used outside the plain JSON driver.

Anyway, I would argue that having the ability to transform schemaless JSON in the Playground is something that could make MDE a bit more approachable to developers who don't have much experience in modeling.

[kolovos]

Correct - to use the YAML flavour you'd need to define an Emfatic metamodel for your JSON document. Adding support for JSON to the playground would require a non-trivial amount of effort including:

• Adding a "format" combo box to all model panels
• Hiding the respective metamodel panel if the "Plain JSON" format is selected
• Updating the code that generates downlowdable copies of the examples
• Updating the backend to also support plain JSON models

I'll leave this issue open, and if there’s sufficient community interest, we can prioritise it accordingly. Any relevant PRs would be more than welcome!

[viht0ri]

The backend already seems to support plain JSON models, at least to some extent. If you rename the first model request property name from flexmi to json, the JSON code path gets executed and the editor seems to produce correct results.

https://github.com/epsilonlabs/playground-backend/blob/bfb922925866b59c244797a25e2c0e4a7896ff39/core/src/main/java/org/eclipse/epsilon/labs/playground/fn/run/RunEpsilonController.java#L312C2-L325C3

[kolovos]

Thanks for pointing this out - I had missed this change in the backend.

[agarciadom]

Ah, I added that for the MDENet Educational Platform - it uses the same backend as the Epsilon Playground :-).

From the frontend side, we'd also need to add JSON highlighting rules to the editor, and add a JSON example that can be tweaked.