DESCRIBE PAGE emits 'database from' for non-database datasources, producing invalid MDL

[TOFBuck]

mxcli version

mxcli version v0.18.0 (2026-08-14T20:29:13Z)

Mendix version

10.24.24.119653

Severity

Medium.

No data is lost and nothing is written incorrectly — but DESCRIBE PAGE output is
not round-trippable for any page hitting this, and it fails at mxcli check with an
error that names the wrong thing, so the cause is not obvious from the message.

It also quietly misinforms a reader about how a page gets its data: a widget fed by a
microflow is rendered as if it read the database directly.

Symptoms

Both are the same defect — the database from keyword is emitted for a datasource that
is not "database over an entity" — but they fail differently.

1. Entity slot left blank

gallery gallery2 (DataSource: database from , Selection: Single, Class: '...') {
                                           ^ nothing here

Also seen with a constraint still attached, which makes it look even more like valid
output:

DataSource: database from  where not(Module.Assoc_A/Module.B),

mxcli check on that:

statement 1: page '...' has reference errors:
- entity not found: from

The parser has taken the keyword from as the entity name.

2. A microflow emitted in the entity slot

line line1 (
  DataSource: database from Module.DS_GetSomeList,
  ...

Module.DS_GetSomeList is a microflow (returns a List), not an entity.
mxcli check:

statement 1: page '...' has reference errors:
- entity not found: Module.DS_GetSomeList

The error blames a missing entity when the real fault is the wrong datasource keyword —
it should have been DataSource: microflow Module.DS_GetSomeList.

DESCRIBE PAGE gets this right elsewhere on the very same page, which is what makes it
a serializer bug rather than a missing feature:

gallery gallery1 (DataSource: microflow Module.DS_GetLocatieListForMap) {   -- correct

Steps to reproduce

Symptom 1 needs a Gallery whose datasource is scoped to a surrounding context rather
than a bare entity (on the project where this was found: seven nested galleries, each
listing the children of the row selected in the gallery one level up).

Symptom 2 needs a pluggable charting widget (a Line chart series) bound to a microflow
datasource.

mxcli -p MyApp.mpr -c "DESCRIBE PAGE MyModule.SomePage" > out.mdl
grep -n "database from" out.mdl        # blank entity, or a microflow name
mxcli check out.mdl -p MyApp.mpr --references

Expected: Check passed! — describing a page and checking the result should be a
no-op. Actual: entity not found: from, or entity not found: <the microflow>.

Expected behaviour

DESCRIBE PAGE output re-checks clean. Specifically:

• A microflow datasource is emitted as DataSource: microflow Module.Flow, never as
  database from Module.Flow.
• A datasource whose entity cannot be resolved is never emitted as a bare
  database from with an empty slot. Emit the resolved entity, or a comment naming
  what could not be serialised — anything the parser will not silently read as an
  entity called from.

Actual behaviour

Measured on two pages in one project, v0.18.0, 2026-08-20:

Page	Line	Emitted	Reality
MyModule.Parent_Edit	6 occurrences	database from (blank)	gallery over a context-scoped source
MyModule.Parent_Edit	1 occurrence	database from where not(...)	same, with constraint retained
MyModule.Dashboard	1 occurrence	database from MyModule.DS_GetSomeList	a microflow returning a List

Both pages fail mxcli check on their own DESCRIBE output.

Workaround

Do not use DESCRIBE PAGE output as a round-trip script. Use targeted ALTER PAGE
operations (SET / INSERT / REPLACE / DROP) instead, which patch in place and do
not require re-emitting the page.

To learn what a widget's datasource really is, read the stored model:

mxcli bson dump -p MyApp.mpr --type page --object MyModule.SomePage > page.json
grep -n 'MicroflowSource\|CustomWidgetXPathSource\|DataViewSource' page.json

Related

Found while testing a separate, more serious defect —
DESCRIBE PAGE silently omits List View specialization templates, reported in
#940. This datasource bug is what blocks that
report's round-trip test before the Mendix-11 page-parameter guard does.

Diagnostic bundle

Yes — mxcli-diag-20260820-132332.tar.gz, available on request. Not attached, because
it contains client model data.

Note on anonymisation

Module and document names above are placeholders. Counts, line positions, emitted
text and error messages are faithful to the real measurement.