fix: map metadata to objectmeta (#292)

* map metadata to objectmeta

On-behalf-of: @SAP a.shcherbatiuk@sap.com
Signed-off-by: Artem Shcherbatiuk <vertex451@gmail.com>

* language

On-behalf-of: @SAP a.shcherbatiuk@sap.com
Signed-off-by: Artem Shcherbatiuk <vertex451@gmail.com>

* use existing field name instead of creating a new one

On-behalf-of: @SAP a.shcherbatiuk@sap.com
Signed-off-by: Artem Shcherbatiuk <vertex451@gmail.com>

* removed allowlist

On-behalf-of: @SAP a.shcherbatiuk@sap.com
Signed-off-by: Artem Shcherbatiuk <vertex451@gmail.com>

* json

On-behalf-of: @SAP a.shcherbatiuk@sap.com
Signed-off-by: Artem Shcherbatiuk <vertex451@gmail.com>

* jsonScalar

On-behalf-of: @SAP a.shcherbatiuk@sap.com
Signed-off-by: Artem Shcherbatiuk <vertex451@gmail.com>

---------

Signed-off-by: Artem Shcherbatiuk <vertex451@gmail.com>

Author: vertex451

gateway/schema/exports_test.go

@@ -3,6 +3,7 @@ package schema
 import "k8s.io/apimachinery/pkg/runtime/schema"
 
 var StringMapScalarForTest = stringMapScalar
+var JSONStringScalarForTest = jsonStringScalar
 
 func GetGatewayForTest(typeNameRegistry map[string]string) *Gateway {
 	return &Gateway{

gateway/schema/scalars.go

@@ -1,6 +1,8 @@
 package schema
 
 import (
+	"encoding/json"
+
 	"github.com/graphql-go/graphql"
 	"github.com/graphql-go/graphql/language/ast"
 )
@@ -34,3 +36,39 @@ var stringMapScalar = graphql.NewScalar(graphql.ScalarConfig{
 		}
 	},
 })
+
+var jsonStringScalar = graphql.NewScalar(graphql.ScalarConfig{
+	Name:        "JSONString",
+	Description: "A JSON-serialized string representation of any object.",
+	Serialize: func(value interface{}) interface{} {
+		// Convert the value to JSON string
+		jsonBytes, err := json.Marshal(value)
+		if err != nil {
+			// Fallback to empty JSON object if marshaling fails
+			return "{}"
+		}
+		return string(jsonBytes)
+	},
+	ParseValue: func(value interface{}) interface{} {
+		if str, ok := value.(string); ok {
+			var result interface{}
+			err := json.Unmarshal([]byte(str), &result)
+			if err != nil {
+				return nil // Invalid JSON
+			}
+			return result
+		}
+		return nil
+	},
+	ParseLiteral: func(valueAST ast.Value) interface{} {
+		if value, ok := valueAST.(*ast.StringValue); ok {
+			var result interface{}
+			err := json.Unmarshal([]byte(value.Value), &result)
+			if err != nil {
+				return nil // Invalid JSON
+			}
+			return result
+		}
+		return nil
+	},
+})

gateway/schema/scalars_test.go

@@ -1,6 +1,7 @@
 package schema_test
 
 import (
+	"encoding/json"
 	"reflect"
 	"testing"
 
@@ -153,3 +154,51 @@ func TestGenerateTypeName(t *testing.T) {
 		})
 	}
 }
+
+func TestJSONStringScalar_ProperSerialization(t *testing.T) {
+	testObject := map[string]interface{}{
+		"name":      "example-config",
+		"namespace": "default",
+		"labels": map[string]string{
+			"hello": "world",
+		},
+		"annotations": map[string]string{
+			"kcp.io/cluster": "root",
+		},
+	}
+
+	// Test the JSONString scalar serialization
+	result := schema.JSONStringScalarForTest.Serialize(testObject)
+
+	if result == nil {
+		t.Fatal("JSONStringScalar.Serialize returned nil")
+	}
+
+	resultStr, ok := result.(string)
+	if !ok {
+		t.Fatalf("JSONStringScalar.Serialize returned %T, expected string", result)
+	}
+
+	// Verify it's valid JSON
+	var parsed map[string]interface{}
+	err := json.Unmarshal([]byte(resultStr), &parsed)
+	if err != nil {
+		t.Fatalf("Result is not valid JSON: %s\nResult: %s", err, resultStr)
+	}
+
+	// Verify the content is preserved
+	if parsed["name"] != "example-config" {
+		t.Errorf("Name not preserved: got %v, want %v", parsed["name"], "example-config")
+	}
+
+	if parsed["namespace"] != "default" {
+		t.Errorf("Namespace not preserved: got %v, want %v", parsed["namespace"], "default")
+	}
+
+	// Verify it's NOT Go map format
+	if len(resultStr) > 10 && resultStr[:4] == "map[" {
+		t.Errorf("Result is in Go map format, not JSON: %s", resultStr)
+	}
+
+	t.Logf("Proper JSON output: %s", resultStr)
+}

gateway/schema/schema.go

@@ -453,8 +453,8 @@ func (g *Gateway) handleObjectFieldSpecType(fieldSpec spec.Schema, typePrefix st
 		}
 	}
 
-	// It's an empty object
-	return graphql.String, graphql.String, nil
+	// It's an empty object, serialize as JSON string
+	return jsonStringScalar, jsonStringScalar, nil
 }
 
 func (g *Gateway) generateTypeName(typePrefix string, fieldPath []string) string {