Fix MPR corruption from dangling GUIDs after attribute drop/add (#4)

The BSON parser was discarding $ID fields from StoredValue, CalculatedValue,
OqlViewValue, and AttributeType objects. The writer then always generated new
UUIDs, leaving orphaned GUID references that caused KeyNotFoundException in
Studio Pro and MxBuild.

Preserve existing $ID through parse→serialize roundtrips; only generate new
UUIDs for newly created attributes.

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

Author: ako

docs/12-bug-reports/issue-4-enumeration-default-guid-corruption.md

@@ -0,0 +1,76 @@
+# Issue #4: MPR Data Corruption After Attribute Drop/Add with Enumeration Default
+
+**Source**: https://github.com/mendixlabs/mxcli/issues/4
+**Severity**: Critical (data loss)
+**Date**: 2026-03-18
+
+## Symptoms
+
+After dropping and re-adding an entity attribute with an enumeration default value, the MPR becomes corrupted. MxBuild/Studio Pro fails with:
+
+```
+System.Collections.Generic.KeyNotFoundException: The given key '3622ee3a-8d34-4495-9788-6e6462f0ab3c' was not present in the dictionary
+```
+
+## Reproduction
+
+```mdl
+ALTER ENTITY MaisonElegance.FormSubmission DROP ATTRIBUTE SubmissionStatus;
+ALTER ENTITY MaisonElegance.FormSubmission ADD ATTRIBUTE SubmissionStatus:
+  Enumeration(MaisonElegance.FormSubmissionStatus) DEFAULT
+  MaisonElegance.FormSubmissionStatus.StatusNew;
+```
+
+## Root Cause
+
+A two-part synchronization failure between the BSON parser and writer for the `$ID` field inside `StoredValue` (and `CalculatedValue`, `OqlViewValue`) objects.
+
+### Part 1: Parser drops the `$ID`
+
+**File**: `sdk/mpr/parser_domainmodel.go`, function `parseAttributeValue()` (lines 224-249)
+
+The parser extracts `$Type` and `DefaultValue` from BSON but never reads `$ID`. The `AttributeValue` struct embeds `BaseElement` (which has an `ID` field via `model.BaseElement`), but the parser never populates it:
+
+```go
+case "DomainModels$StoredValue":
+    return &domainmodel.AttributeValue{
+        Type:         "StoredValue",
+        DefaultValue: defaultValue,
+        // $ID is never extracted from raw — lost here
+    }
+```
+
+### Part 2: Writer always generates a new GUID
+
+**File**: `sdk/mpr/writer_domainmodel.go`, function `serializeAttribute()` (lines 823-827)
+
+The writer always calls `generateUUID()` for the StoredValue's `$ID`, never checking if an existing ID should be preserved:
+
+```go
+valueDoc = bson.D{
+    {Key: "$ID", Value: idToBsonBinary(generateUUID())},  // always new
+    {Key: "$Type", Value: "DomainModels$StoredValue"},
+    {Key: "DefaultValue", Value: defaultValue},
+}
+```
+
+### The Corruption Flow
+
+1. **Read MPR**: StoredValue has `$ID: "3622ee3a-..."` in BSON
+2. **Parser drops `$ID`**: `AttributeValue.ID` is empty string
+3. **DROP ATTRIBUTE**: Removes the attribute from the entity's attribute list, but the old GUID remains referenced elsewhere in the MPR (GUID registry, cross-references)
+4. **ADD ATTRIBUTE**: Writer generates a brand new UUID for the StoredValue
+5. **Old GUID becomes orphaned**: Studio Pro resolves all GUID references, finds `"3622ee3a-..."` pointing to nothing → `KeyNotFoundException`
+
+## Impact Scope
+
+- Affects **all** attribute value types, not just enumerations (StoredValue, CalculatedValue, OqlViewValue)
+- Any DROP + ADD attribute cycle on an attribute with a default value will produce orphaned GUIDs
+- Multiple drop/add cycles compound the problem with more orphaned GUIDs
+- Corrupted MPR cannot be opened in Studio Pro or built with MxBuild
+- No workaround exists beyond reverting to backups
+
+## Fix Required
+
+1. **`sdk/mpr/parser_domainmodel.go`** — Extract `$ID` from the BSON `raw` map and set it on `AttributeValue.BaseElement.ID` for all value types (StoredValue, CalculatedValue, OqlViewValue)
+2. **`sdk/mpr/writer_domainmodel.go`** — If `a.Value.ID` is non-empty, preserve it instead of generating a new UUID. Only generate a new UUID for truly new attributes (where `ID` is empty).

mdl/executor/roundtrip_mxcheck_test.go

@@ -458,6 +458,68 @@ func TestMxCheck_CE0066_Scenarios(t *testing.T) {
 	}
 }
 
+// TestMxCheck_DropAddEnumAttribute validates that dropping and re-adding an attribute
+// with an enumeration default value does not corrupt the MPR (GitHub issue #4).
+// Before the fix, the StoredValue $ID was lost during parsing and a new GUID was
+// generated on write, leaving dangling references that caused KeyNotFoundException.
+func TestMxCheck_DropAddEnumAttribute(t *testing.T) {
+	if !mxCheckAvailable() {
+		t.Skip("mx command not available")
+	}
+
+	env := setupTestEnv(t)
+	defer env.teardown()
+
+	mod := testModule
+
+	// Step 1: Create an enumeration and an entity with an enumeration attribute
+	setupMDL := strings.Join([]string{
+		`CREATE ENUMERATION ` + mod + `.SubmissionStatus (StatusNew 'New', StatusInProgress 'In Progress', StatusDone 'Done');`,
+		`CREATE OR MODIFY PERSISTENT ENTITY ` + mod + `.Issue4Entity (
+			Name: String(100),
+			Status: Enumeration(` + mod + `.SubmissionStatus) DEFAULT ` + mod + `.SubmissionStatus.StatusNew
+		);`,
+	}, "\n")
+
+	prog, errs := visitor.Build(setupMDL)
+	if len(errs) > 0 {
+		t.Fatalf("Parse failed: %v\nMDL:\n%s", errs[0], setupMDL)
+	}
+	if err := env.executor.ExecuteProgram(prog); err != nil {
+		t.Fatalf("Setup failed: %v", err)
+	}
+
+	// Step 2: Drop the attribute and re-add it with a different default
+	alterMDL := strings.Join([]string{
+		`ALTER ENTITY ` + mod + `.Issue4Entity DROP ATTRIBUTE Status;`,
+		`ALTER ENTITY ` + mod + `.Issue4Entity ADD ATTRIBUTE Status: Enumeration(` + mod + `.SubmissionStatus) DEFAULT ` + mod + `.SubmissionStatus.StatusInProgress;`,
+	}, "\n")
+
+	prog, errs = visitor.Build(alterMDL)
+	if len(errs) > 0 {
+		t.Fatalf("Parse failed: %v\nMDL:\n%s", errs[0], alterMDL)
+	}
+	if err := env.executor.ExecuteProgram(prog); err != nil {
+		t.Fatalf("Alter failed: %v", err)
+	}
+
+	// Step 3: Flush to disk and validate with mx check
+	env.executor.Execute(&ast.DisconnectStmt{})
+
+	output, err := runMxCheck(t, env.projectPath)
+	if err != nil {
+		if strings.Contains(output, "KeyNotFoundException") || strings.Contains(output, "not present in the dictionary") {
+			t.Errorf("Issue #4 regression: dangling GUID reference after drop/add enum attribute:\n%s", output)
+		} else if strings.Contains(output, "error") || strings.Contains(output, "Error") {
+			t.Errorf("mx check found errors:\n%s", output)
+		} else {
+			t.Logf("mx check output (non-zero exit but no errors):\n%s", output)
+		}
+	} else {
+		t.Logf("mx check passed")
+	}
+}
+
 // TestMxCheck_RetrieveWithDateTimeToken validates that RETRIEVE with [%CurrentDateTime%]
 // in a WHERE clause produces correctly quoted XPath (GitHub issue #1).
 // The token must be quoted as '[%CurrentDateTime%]' in XPath constraints.

sdk/mpr/parser_domainmodel.go

@@ -224,56 +224,77 @@ func parseAttribute(raw map[string]any) *domainmodel.Attribute {
 func parseAttributeValue(raw map[string]any) *domainmodel.AttributeValue {
 	typeName := extractString(raw["$Type"])
 	defaultValue := extractString(raw["DefaultValue"])
+	valueID := model.ID(extractBsonID(raw["$ID"]))
 
 	switch typeName {
 	case "DomainModels$StoredValue":
-		return &domainmodel.AttributeValue{
+		val := &domainmodel.AttributeValue{
 			Type:         "StoredValue",
 			DefaultValue: defaultValue,
 		}
+		val.ID = valueID
+		return val
 	case "DomainModels$CalculatedValue":
-		return &domainmodel.AttributeValue{
+		val := &domainmodel.AttributeValue{
 			Type:        "CalculatedValue",
 			MicroflowID: model.ID(extractBsonID(raw["Microflow"])),
 		}
+		val.ID = valueID
+		return val
 	case "DomainModels$OqlViewValue":
-		return &domainmodel.AttributeValue{
+		val := &domainmodel.AttributeValue{
 			Type:          "OqlViewValue",
 			ViewReference: extractString(raw["Reference"]),
 		}
+		val.ID = valueID
+		return val
 	default:
-		return &domainmodel.AttributeValue{
+		val := &domainmodel.AttributeValue{
 			DefaultValue: defaultValue,
 		}
+		val.ID = valueID
+		return val
 	}
 }
 
 func parseAttributeType(raw map[string]any) domainmodel.AttributeType {
 	typeName, _ := raw["$Type"].(string)
+	typeID := model.ID(extractBsonID(raw["$ID"]))
 
 	switch typeName {
 	case "DomainModels$StringAttributeType":
 		t := &domainmodel.StringAttributeType{}
+		t.ID = typeID
 		if length, ok := raw["Length"].(int32); ok {
 			t.Length = int(length)
 		}
 		return t
 	case "DomainModels$IntegerAttributeType":
-		return &domainmodel.IntegerAttributeType{}
+		t := &domainmodel.IntegerAttributeType{}
+		t.ID = typeID
+		return t
 	case "DomainModels$LongAttributeType":
-		return &domainmodel.LongAttributeType{}
+		t := &domainmodel.LongAttributeType{}
+		t.ID = typeID
+		return t
 	case "DomainModels$DecimalAttributeType":
-		return &domainmodel.DecimalAttributeType{}
+		t := &domainmodel.DecimalAttributeType{}
+		t.ID = typeID
+		return t
 	case "DomainModels$BooleanAttributeType":
-		return &domainmodel.BooleanAttributeType{}
+		t := &domainmodel.BooleanAttributeType{}
+		t.ID = typeID
+		return t
 	case "DomainModels$DateTimeAttributeType":
 		t := &domainmodel.DateTimeAttributeType{}
+		t.ID = typeID
 		if localize, ok := raw["LocalizeDate"].(bool); ok {
 			t.LocalizeDate = localize
 		}
 		return t
 	case "DomainModels$EnumerationAttributeType":
 		t := &domainmodel.EnumerationAttributeType{}
+		t.ID = typeID
 		// Enumeration is stored as qualified name string (BY_NAME_REFERENCE)
 		if enumRef, ok := raw["Enumeration"].(string); ok {
 			t.EnumerationRef = enumRef
@@ -282,13 +303,21 @@ func parseAttributeType(raw map[string]any) domainmodel.AttributeType {
 		}
 		return t
 	case "DomainModels$AutoNumberAttributeType":
-		return &domainmodel.AutoNumberAttributeType{}
+		t := &domainmodel.AutoNumberAttributeType{}
+		t.ID = typeID
+		return t
 	case "DomainModels$BinaryAttributeType":
-		return &domainmodel.BinaryAttributeType{}
+		t := &domainmodel.BinaryAttributeType{}
+		t.ID = typeID
+		return t
 	case "DomainModels$HashedStringAttributeType":
-		return &domainmodel.HashedStringAttributeType{}
+		t := &domainmodel.HashedStringAttributeType{}
+		t.ID = typeID
+		return t
 	default:
-		return &domainmodel.StringAttributeType{} // Default fallback
+		t := &domainmodel.StringAttributeType{} // Default fallback
+		t.ID = typeID
+		return t
 	}
 }
 

sdk/mpr/writer_domainmodel.go

@@ -785,8 +785,14 @@ func serializeAttribute(a *domainmodel.Attribute) bson.D {
 		typeName = "DomainModels$" + a.Type.GetTypeName() + "AttributeType"
 	}
 
+	attrTypeID := generateUUID()
+	if a.Type != nil {
+		if elem, ok := a.Type.(model.Element); ok && elem.GetID() != "" {
+			attrTypeID = string(elem.GetID())
+		}
+	}
 	attrType := bson.D{
-		{Key: "$ID", Value: idToBsonBinary(generateUUID())},
+		{Key: "$ID", Value: idToBsonBinary(attrTypeID)},
 		{Key: "$Type", Value: typeName},
 	}
 	// Add type-specific properties
@@ -807,10 +813,17 @@ func serializeAttribute(a *domainmodel.Attribute) bson.D {
 
 	// Determine value type: OqlViewValue for view entities, StoredValue for regular entities
 	var valueDoc bson.D
+	valueID := ""
+	if a.Value != nil && a.Value.ID != "" {
+		valueID = string(a.Value.ID)
+	}
+	if valueID == "" {
+		valueID = generateUUID()
+	}
 	if a.Value != nil && a.Value.ViewReference != "" {
 		// View entity attribute - use OqlViewValue
 		valueDoc = bson.D{
-			{Key: "$ID", Value: idToBsonBinary(generateUUID())},
+			{Key: "$ID", Value: idToBsonBinary(valueID)},
 			{Key: "$Type", Value: "DomainModels$OqlViewValue"},
 			{Key: "Reference", Value: a.Value.ViewReference},
 		}
@@ -821,7 +834,7 @@ func serializeAttribute(a *domainmodel.Attribute) bson.D {
 			defaultValue = a.Value.DefaultValue
 		}
 		valueDoc = bson.D{
-			{Key: "$ID", Value: idToBsonBinary(generateUUID())},
+			{Key: "$ID", Value: idToBsonBinary(valueID)},
 			{Key: "$Type", Value: "DomainModels$StoredValue"},
 			{Key: "DefaultValue", Value: defaultValue},
 		}