create json structure builds different element metadata than Studio Pro — array items named "DataItem" not "Datum", root MinOccurs 0 not 1

create json structure … snippet '…' produces a document whose element metadata
differs from the one Studio Pro writes for the same snippet, in two ways. Both
are silent, and both leak into every mapping built over the structure — a mapping
element clones ExposedName, MinOccurs, MaxOccurs and Nillable from the
structure it resolves against.

Measured

Studio Pro's KrogerAPI.JSON_Location (CitrusGrove demo app) beside mxcli's
structure for a snippet of the same shape ({"data": [{…}], "meta": {…}}), both
Mendix 11.13.0:

element	Studio Pro	mxcli
root `(Object)`	`MinOccurs 1`	`MinOccurs 0`
array item `(Object)\|data\|(Object)`	`ExposedName "Datum"`	`"DataItem"`
array item `…\|departments\|(Object)`	`ExposedName "Department"`	(n/a — same rule)

Studio Pro singularises the array's name for its item element — Data →
Datum, Departments → Department, real English singularisation rather than
stripping a trailing "s". mxcli appends Item
(mdl/types/json_utils.go, and the elem.ExposedName + "Item" fallback in
mdl/executor/cmd_export_mappings.go).

Why it matters beyond cosmetics

ExposedName is one of the two names a mapping member resolves by (#882), so a
mapping authored against an mxcli-built structure carries DataItem where the
same mapping authored in Studio Pro carries Datum. The documents are no longer
interchangeable, and a describe → exec round trip of a Studio Pro mapping over
an mxcli-rebuilt structure rewrites the stored element.

That is exactly how this was found. In the round-trip fixture
(mdl/executor/testdata/mapping-fixtures/), KrogerAPI.IM_Location — a real
Studio Pro mapping that uses nothing outside MDL's expressive range — did not
round-trip while its JSON structure was regenerated from its snippet:

DIFF /Elements/1/Children/1/ExposedName  'Datum' -> 'DataItem'
DIFF /Elements/1/MinOccurs               1       -> 0

Transplanting the structure verbatim instead makes the same mapping round-trip
exactly, which isolates the defect to the structure builder rather than the
mapping describer. IM_Location is now the fixture's real-document control for
that reason.

Suggested

Match Studio Pro's item naming, including the singularisation. It is worth
checking what rule Mendix actually uses (it is not a plain "drop the s" —
data → Datum is Latin) before reimplementing it; a reference structure per
shape is cheap to produce.
Give the root MinOccurs 1.
A test comparing an mxcli-built structure against a Studio-Pro-built one over
the same snippet, element by element — the same methodology used for the
scheduled-event and rule documents.

Measured on 70a12365 / ed0eda6d, Mendix 11.13.0. Context:
docs/11-proposals/PROPOSAL_mapping_coverage.md, and the fixture README.

test(mappings): add the DESCRIBE round-trip test, and pin JSON struct…

Another instance, found while fixing #277/#279 and not fixed there (out of scope):

mxcli gives a JSON structure's ROOT element MinOccurs 0; Studio Pro writes 1.

Uniform across all nine Studio Pro-authored structures pinned in
mdl/executor/testdata/mapping-fixtures/:

FeedbackModule.JSON_AppInsightsRequest.bson    root=[('Object', 1)]
FeedbackModule.JSON_AppInsightsResponse.bson   root=[('Object', 1)]
KrogerAPI.JSON_AccessToken.bson                root=[('Object', 1)]
KrogerAPI.JSON_Location.bson                   root=[('Object', 1)]
KrogerAPI.JSON_ProductList.bson                root=[('Object', 1)]
MxGenAIConnector.JSON_CohereEmbed_Request.bson root=[('Object', 1)]
MxGenAIConnector.JSON_Collection_Retrieve…     root=[('Object', 1)]
MxGenAIConnector.JSON_InvokeModel_Cohere…      root=[('Object', 1)]
OpenAI_API.JSON_OpenAI_Response.bson           root=[('Object', 1)]

An mxcli-built structure from {"title":"t","width":1,"height":2}:

Object  min=0   max=1   maxLen=-1   (Object)
  Value   min=0   max=1   maxLen=0    title
  Value   min=0   max=1   maxLen=-1   width
  Value   min=0   max=1   maxLen=-1   height

Everything except the root's MinOccurs matches — including MaxLength 0 for
the string and -1 for the numbers, which #277 confirmed the mapping must mirror.

It surfaced because export mapping elements now mirror the bound schema element
(#277): a mapping over a Studio Pro structure gets a root MinOccurs of 1,
one over an mxcli-built structure gets 0. So the mapping side is correct and
the discrepancy is entirely here.

Measured on mxbuild 11.13. Note it is not a build error — mx check reports 0
errors either way — so it is diff churn against a Studio Pro original, the same
class as the rest of this issue.

A second instance, found while fixing #260 and again not fixed there:

create json structure does not sanitise a member name into a valid custom name.

create json structure X snippet '{"$type": "weird"}';

[error] [CE9524] "JSON element '(Object)/$type' has an invalid custom name '$type'.
        Custom name should start with a letter or underscore followed by either
        letters, digits or underscores."

Here the message is accurate — unlike the owner case in #300, where it
quoted a pattern the name already satisfied. capitalizeFirst("$type") is
$type, which genuinely starts with an invalid character.

Studio Pro sanitises. From Evora-FactoryManagement's
CRS_ModelSimulator/Request mapping, whose members contain parentheses and
spaces:

confidence(No)       -> Confidence_No_
prediction(Breakdown)-> Prediction_Breakdown_
Support Prediction   -> Support_Prediction
weights__base        -> Weights__base

So the rule is: replace every character that is not a letter, digit or
underscore with _, then capitalise the initial — and if the result still does
not start with a letter or underscore, it needs a prefix (Studio Pro's _id /
_object handling from #300 is the same mechanism).

Consequence: the 5 documents #260 lists as carrying unspellable members
($type, 43 occurrences; research%3Aread;
https%3A//sws.siemens.com/sam/claims/tenantId) cannot be reproduced by mxcli at
all — a structure containing one fails to build. #260's describer fix makes such
a member describable into MDL that parses (T = "$type", since
identifierOrKeyword already accepts a quoted identifier), which covers reading
an existing Studio Pro document; creating one still needs this.

Measured on mxbuild 11.13.

feat(json): let a script name an array's item element

test(messagedefs): skip the doctype example on the legacy engine

docs(proposal): spec authorable message definitions

feat(messagedefs): grammar, AST and visitor for message definition co…

feat(messagedefs): storage — semantic type, codec writer, both engines

fix(messagedefs): three derivations corrected against a real Studio P…

feat(messagedefs): executor — create, alter, describe, show, drop

docs(messagedefs): example, skill, site reference, syntax help, finding

docs(changelog): release v0.21.0

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create json structure builds different element metadata than Studio Pro — array items named "DataItem" not "Datum", root MinOccurs 0 not 1 #272

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create json structure builds different element metadata than Studio Pro — array items named "DataItem" not "Datum", root MinOccurs 0 not 1 #272

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ako commented on Aug 27, 2026

ako commented on Aug 27, 2026

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