Add MDL

Add export mapping

Author: khode-mx

CLAUDE.md

@@ -2,6 +2,12 @@
 
 This file provides guidance for Claude Code when working with this repository.
 
+## Canonical Test Project Path
+
+**ALWAYS use:** `/Users/Dennis.Kho/Sandbox/KhodeClaudeLab-main/KhodeClaudeLab.mpr`
+
+A disposable test copy exists at `/tmp/KhodeClaudeLab-test/` — **never use it for `mxcli exec` or write operations**. Before running any `mxcli -p <path> exec` command, verify the path starts with `/Users/Dennis.Kho/Sandbox/KhodeClaudeLab-main/`. If the path points to `/tmp/` or any other copy, stop and correct it first.
+
 ## Project Overview
 
 **ModelSDK Go** is a Go library for reading and modifying Mendix application projects (`.mpr` files) stored locally on disk. It's a Go-native alternative to the TypeScript-based Mendix Model SDK, enabling programmatic access without cloud connectivity.
@@ -151,6 +157,19 @@ When adding new types, always verify the storage name by:
 
 **IMPORTANT**: When unsure about the correct BSON structure for a new feature, **ask the user to create a working example in Mendix Studio Pro** so you can compare the generated BSON against a known-good reference.
 
+### Generated Metamodel $Type Naming Trap (MappingElements)
+
+**CRITICAL**: The Go struct names in `generated/metamodel/types.go` are NOT reliable sources for BSON `$Type` strings. The generated code embeds the namespace word in element type names, but the real Mendix BSON does NOT.
+
+| Go struct (WRONG as $Type) | Correct BSON $Type |
+|----------------------------|--------------------|
+| `ImportMappingsImportObjectMappingElement` | `ImportMappings$ObjectMappingElement` |
+| `ImportMappingsImportValueMappingElement` | `ImportMappings$ValueMappingElement` |
+| `ExportMappingsExportObjectMappingElement` | `ExportMappings$ObjectMappingElement` |
+| `ExportMappingsExportValueMappingElement` | `ExportMappings$ValueMappingElement` |
+
+**Rule**: MappingElement `$Type` names follow `Namespace$ElementKind` — the namespace prefix word is never repeated inside the element name. Both mistakes have been encountered in production and caused `TypeCacheUnknownTypeException`. Always verify against the working writer code (`writer_import_mapping.go`, `writer_export_mapping.go`) or a Studio Pro-created MPR before writing a new mapping serializer.
+
 ### Pluggable Widget Templates
 
 For pluggable widgets (DataGrid2, ComboBox, Gallery, etc.), templates must include **both** `type` AND `object` fields:

mdl/ast/ast_json_structure.go

@@ -64,3 +64,44 @@ type ImportMappingElementDef struct {
 	DataType  string // "String", "Integer", "Boolean", "Decimal", "DateTime"
 	IsKey     bool
 }
+
+// ============================================================================
+// Export Mapping Statements
+// ============================================================================
+
+// CreateExportMappingStmt represents:
+//
+//	CREATE EXPORT MAPPING Module.Name
+//	  [TO JSON STRUCTURE Module.JsonStructure | TO XML SCHEMA Module.Schema]
+//	  [NULL VALUES LeaveOutElement | SendAsNil]
+//	{ Module.Entity -> root { ... } }
+type CreateExportMappingStmt struct {
+	Name            QualifiedName
+	SchemaKind      string        // "JSON_STRUCTURE" or "XML_SCHEMA" or ""
+	SchemaRef       QualifiedName // qualified name of the schema source
+	NullValueOption string        // "LeaveOutElement" or "SendAsNil" (default: "LeaveOutElement")
+	RootElement     *ExportMappingElementDef
+}
+
+func (s *CreateExportMappingStmt) isStatement() {}
+
+// DropExportMappingStmt represents: DROP EXPORT MAPPING Module.Name
+type DropExportMappingStmt struct {
+	Name QualifiedName
+}
+
+func (s *DropExportMappingStmt) isStatement() {}
+
+// ExportMappingElementDef represents one element in an export mapping tree.
+// It may be an object mapping (entity → JSON key) or a value mapping (attribute → JSON key).
+type ExportMappingElementDef struct {
+	// JSON field name (the RHS of ->)
+	JsonName string
+	// Object mapping fields (set when mapping from an entity)
+	Entity      string // qualified entity name (e.g. "Module.Customer")
+	Association string // qualified association name for VIA clause
+	Children    []*ExportMappingElementDef
+	// Value mapping fields (set when mapping from an attribute)
+	Attribute string // attribute name (unqualified, e.g. "Name")
+	DataType  string // "String", "Integer", "Boolean", "Decimal", "DateTime"
+}

mdl/ast/ast_query.go

@@ -86,6 +86,7 @@ const (
 	ShowContractMessages     // SHOW CONTRACT MESSAGES FROM Module.Service (AsyncAPI)
 	ShowJsonStructures       // SHOW JSON STRUCTURES [IN module]
 	ShowImportMappings       // SHOW IMPORT MAPPINGS [IN module]
+	ShowExportMappings       // SHOW EXPORT MAPPINGS [IN module]
 )
 
 // String returns the human-readable name of the show object type.
@@ -205,6 +206,8 @@ func (t ShowObjectType) String() string {
 		return "JSON STRUCTURES"
 	case ShowImportMappings:
 		return "IMPORT MAPPINGS"
+	case ShowExportMappings:
+		return "EXPORT MAPPINGS"
 	default:
 		return "UNKNOWN"
 	}
@@ -262,6 +265,7 @@ const (
 	DescribeContractMessage      // DESCRIBE CONTRACT MESSAGE Service.MessageName
 	DescribeJsonStructure        // DESCRIBE JSON STRUCTURE Module.Name
 	DescribeImportMapping        // DESCRIBE IMPORT MAPPING Module.Name
+	DescribeExportMapping        // DESCRIBE EXPORT MAPPING Module.Name
 )
 
 // String returns the human-readable name of the describe object type.
@@ -329,6 +333,8 @@ func (t DescribeObjectType) String() string {
 		return "JSON STRUCTURE"
 	case DescribeImportMapping:
 		return "IMPORT MAPPING"
+	case DescribeExportMapping:
+		return "EXPORT MAPPING"
 	default:
 		return "UNKNOWN"
 	}