Fix COMBOBOX association: set EntityRef via IndirectEntityRef with association path

The COMBOBOX widget in association mode was missing the Entity property
(CE0642) because the pluggable widget's attributeAssociation WidgetValue
needs an EntityRef with the target entity resolved through the association.

Uses DomainModels$IndirectEntityRef with a Steps array containing the
association path and destination entity, which is how Mendix resolves
entity references through associations in pluggable widgets.

The integration test now validates the full COMBOBOX association flow
passes mx check with zero errors (no more CE0642, CE8812, or CE1613).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ako

mdl/executor/cmd_pages_builder_input.go

@@ -172,14 +172,39 @@ func setDataSource(val bson.D, ds pages.DataSource) bson.D {
 	return result
 }
 
-// setAssociationRef sets the AttributeRef field in a WidgetValue for an association binding.
-// Uses DomainModels$AttributeRef with Attribute field — the WidgetValue.AttributeRef property
-// in C# is statically typed as AttributeRef (not polymorphic MemberRef), so we cannot use
-// DomainModels$AssociationRef. The association is stored as a 3-part member path
-// Module.Entity.AssociationName (same format as attributes), and Mendix resolves it as a
-// member of the entity.
-func setAssociationRef(val bson.D, assocPath string) bson.D {
-	return setAttributeRef(val, assocPath)
+// setAssociationRef sets the AttributeRef and EntityRef fields in a WidgetValue for an
+// association binding on a pluggable widget.
+// - assocPath: qualified association name (Module.AssociationName)
+// - entityName: target entity qualified name (Module.EntityName)
+// MxBuild requires both: AttributeRef with the association path (CE8812) and
+// EntityRef with the target entity (CE0642).
+// setAssociationRef sets the EntityRef field in a WidgetValue for an association binding
+// on a pluggable widget. Uses DomainModels$IndirectEntityRef which resolves through an
+// association path. MxBuild requires both the entity reference and association path (CE0642, CE8812).
+// The assocPath is the qualified association name (Module.AssociationName).
+// The entityName is the target entity qualified name (Module.EntityName).
+func setAssociationRef(val bson.D, assocPath string, entityName string) bson.D {
+	result := make(bson.D, 0, len(val))
+	for _, elem := range val {
+		if elem.Key == "EntityRef" && entityName != "" {
+			result = append(result, bson.E{Key: "EntityRef", Value: bson.D{
+				{Key: "$ID", Value: mpr.IDToBsonBinary(mpr.GenerateID())},
+				{Key: "$Type", Value: "DomainModels$IndirectEntityRef"},
+				{Key: "Steps", Value: bson.A{
+					int32(2), // version marker
+					bson.D{
+						{Key: "$ID", Value: mpr.IDToBsonBinary(mpr.GenerateID())},
+						{Key: "$Type", Value: "DomainModels$IndirectEntityRefStep"},
+						{Key: "Association", Value: assocPath},
+						{Key: "DestinationEntity", Value: entityName},
+					},
+				}},
+			}})
+		} else {
+			result = append(result, elem)
+		}
+	}
+	return result
 }
 
 // setAttributeRef sets the AttributeRef field in a WidgetValue.

mdl/executor/cmd_pages_builder_v3_pluggable.go

@@ -59,13 +59,13 @@ func (pb *pageBuilder) buildComboBoxV3(w *ast.WidgetV3) (*pages.CustomWidget, er
 			return nil, fmt.Errorf("failed to build ComboBox datasource: %w", err)
 		}
 
-		// 3. Set attributeAssociation — this is the association name (e.g., Order_Customer)
-		// resolved to a 3-part member path: Module.Entity.AssociationName
-		// (same format as attributes, since associations are entity members)
+		// 3. Set attributeAssociation — association path + target entity
+		// MxBuild requires both: association path in AttributeRef (CE8812) and
+		// target entity in EntityRef (CE0642)
 		if attr := w.GetAttribute(); attr != "" {
 			assocPath := pb.resolveAssociationPath(attr)
 			updatedObject = updateWidgetPropertyValue(updatedObject, propertyTypeIDs, "attributeAssociation", func(val bson.D) bson.D {
-				return setAssociationRef(val, assocPath)
+				return setAssociationRef(val, assocPath, entityName)
 			})
 		}
 

mdl/executor/roundtrip_mxcheck_test.go

@@ -830,15 +830,12 @@ END;`
 	if err != nil {
 		if strings.Contains(output, "no longer exists") {
 			t.Errorf("mx check reports attribute no longer exists (association not resolved correctly):\n%s", output)
+		} else if strings.Contains(output, "CE0642") {
+			t.Errorf("mx check reports Entity property missing on ComboBox (association EntityRef not set):\n%s", output)
+		} else if strings.Contains(output, "CE8812") {
+			t.Errorf("mx check reports association path missing on ComboBox:\n%s", output)
 		} else if strings.Contains(output, "error") || strings.Contains(output, "Error") {
-			// CE0642 "Property 'Entity' is required" on the DataView is a known
-			// limitation of microflow-sourced dataviews — not related to the
-			// ComboBox association fix under test.
-			if strings.Contains(output, "CE0642") && !strings.Contains(output, "no longer exists") {
-				t.Logf("mx check has unrelated DataView error (CE0642), ComboBox association resolved correctly:\n%s", output)
-			} else {
-				t.Errorf("mx check found errors:\n%s", output)
-			}
+			t.Errorf("mx check found errors:\n%s", output)
 		} else {
 			t.Logf("mx check output:\n%s", output)
 		}