fix(recursive_crud): 🐛 prevent overwriting primary key in recursive relationships

* Ensure foreign key assignment does not overwrite primary key in recursive relationships.
* Added logging for skipped assignments to improve debugging.

pkg/common/recursive_crud.go

@@ -74,6 +74,7 @@ func (p *NestedCUDProcessor) ProcessNestedCUD(
 	}
 
 	if modelType == nil || modelType.Kind() != reflect.Struct {
+		logger.Error("Invalid model type: operation=%s, table=%s, modelType=%v, expected struct", operation, tableName, modelType)
 		return nil, fmt.Errorf("model must be a struct type, got %v", modelType)
 	}
 
@@ -103,44 +104,64 @@ func (p *NestedCUDProcessor) ProcessNestedCUD(
 	// Get the primary key name for this model
 	pkName := reflection.GetPrimaryKeyName(model)
 
+	// Check if we have any data to process (besides _request)
+	hasData := len(regularData) > 0
+
 	// Process based on operation
 	switch strings.ToLower(operation) {
 	case "insert", "create":
-		id, err := p.processInsert(ctx, regularData, tableName)
-		if err != nil {
-			return nil, fmt.Errorf("insert failed: %w", err)
-		}
-		result.ID = id
-		result.AffectedRows = 1
-		result.Data = regularData
+		// Only perform insert if we have data to insert
+		if hasData {
+			id, err := p.processInsert(ctx, regularData, tableName)
+			if err != nil {
+				logger.Error("Insert failed for table=%s, data=%+v, error=%v", tableName, regularData, err)
+				return nil, fmt.Errorf("insert failed: %w", err)
+			}
+			result.ID = id
+			result.AffectedRows = 1
+			result.Data = regularData
 
-		// Process child relations after parent insert (to get parent ID)
-		if err := p.processChildRelations(ctx, "insert", id, relationFields, result.RelationData, modelType); err != nil {
-			return nil, fmt.Errorf("failed to process child relations: %w", err)
+			// Process child relations after parent insert (to get parent ID)
+			if err := p.processChildRelations(ctx, "insert", id, relationFields, result.RelationData, modelType, parentIDs); err != nil {
+				logger.Error("Failed to process child relations after insert: table=%s, parentID=%v, relations=%+v, error=%v", tableName, id, relationFields, err)
+				return nil, fmt.Errorf("failed to process child relations: %w", err)
+			}
+		} else {
+			logger.Debug("Skipping insert for %s - no data columns besides _request", tableName)
 		}
 
 	case "update":
-		rows, err := p.processUpdate(ctx, regularData, tableName, data[pkName])
-		if err != nil {
-			return nil, fmt.Errorf("update failed: %w", err)
-		}
-		result.ID = data[pkName]
-		result.AffectedRows = rows
-		result.Data = regularData
+		// Only perform update if we have data to update
+		if hasData {
+			rows, err := p.processUpdate(ctx, regularData, tableName, data[pkName])
+			if err != nil {
+				logger.Error("Update failed for table=%s, id=%v, data=%+v, error=%v", tableName, data[pkName], regularData, err)
+				return nil, fmt.Errorf("update failed: %w", err)
+			}
+			result.ID = data[pkName]
+			result.AffectedRows = rows
+			result.Data = regularData
 
-		// Process child relations for update
-		if err := p.processChildRelations(ctx, "update", data[pkName], relationFields, result.RelationData, modelType); err != nil {
-			return nil, fmt.Errorf("failed to process child relations: %w", err)
+			// Process child relations for update
+			if err := p.processChildRelations(ctx, "update", data[pkName], relationFields, result.RelationData, modelType, parentIDs); err != nil {
+				logger.Error("Failed to process child relations after update: table=%s, parentID=%v, relations=%+v, error=%v", tableName, data[pkName], relationFields, err)
+				return nil, fmt.Errorf("failed to process child relations: %w", err)
+			}
+		} else {
+			logger.Debug("Skipping update for %s - no data columns besides _request", tableName)
+			result.ID = data[pkName]
 		}
 
 	case "delete":
 		// Process child relations first (for referential integrity)
-		if err := p.processChildRelations(ctx, "delete", data[pkName], relationFields, result.RelationData, modelType); err != nil {
+		if err := p.processChildRelations(ctx, "delete", data[pkName], relationFields, result.RelationData, modelType, parentIDs); err != nil {
+			logger.Error("Failed to process child relations before delete: table=%s, id=%v, relations=%+v, error=%v", tableName, data[pkName], relationFields, err)
 			return nil, fmt.Errorf("failed to process child relations before delete: %w", err)
 		}
 
 		rows, err := p.processDelete(ctx, tableName, data[pkName])
 		if err != nil {
+			logger.Error("Delete failed for table=%s, id=%v, error=%v", tableName, data[pkName], err)
 			return nil, fmt.Errorf("delete failed: %w", err)
 		}
 		result.ID = data[pkName]
@@ -148,6 +169,7 @@ func (p *NestedCUDProcessor) ProcessNestedCUD(
 		result.Data = regularData
 
 	default:
+		logger.Error("Unsupported operation: %s for table=%s", operation, tableName)
 		return nil, fmt.Errorf("unsupported operation: %s", operation)
 	}
 
@@ -213,6 +235,7 @@ func (p *NestedCUDProcessor) processInsert(
 
 	result, err := query.Exec(ctx)
 	if err != nil {
+		logger.Error("Insert execution failed: table=%s, data=%+v, error=%v", tableName, data, err)
 		return nil, fmt.Errorf("insert exec failed: %w", err)
 	}
 
@@ -236,6 +259,7 @@ func (p *NestedCUDProcessor) processUpdate(
 	id interface{},
 ) (int64, error) {
 	if id == nil {
+		logger.Error("Update requires an ID: table=%s, data=%+v", tableName, data)
 		return 0, fmt.Errorf("update requires an ID")
 	}
 
@@ -245,6 +269,7 @@ func (p *NestedCUDProcessor) processUpdate(
 
 	result, err := query.Exec(ctx)
 	if err != nil {
+		logger.Error("Update execution failed: table=%s, id=%v, data=%+v, error=%v", tableName, id, data, err)
 		return 0, fmt.Errorf("update exec failed: %w", err)
 	}
 
@@ -256,6 +281,7 @@ func (p *NestedCUDProcessor) processUpdate(
 // processDelete handles delete operation
 func (p *NestedCUDProcessor) processDelete(ctx context.Context, tableName string, id interface{}) (int64, error) {
 	if id == nil {
+		logger.Error("Delete requires an ID: table=%s", tableName)
 		return 0, fmt.Errorf("delete requires an ID")
 	}
 
@@ -265,6 +291,7 @@ func (p *NestedCUDProcessor) processDelete(ctx context.Context, tableName string
 
 	result, err := query.Exec(ctx)
 	if err != nil {
+		logger.Error("Delete execution failed: table=%s, id=%v, error=%v", tableName, id, err)
 		return 0, fmt.Errorf("delete exec failed: %w", err)
 	}
 
@@ -281,6 +308,7 @@ func (p *NestedCUDProcessor) processChildRelations(
 	relationFields map[string]*RelationshipInfo,
 	relationData map[string]interface{},
 	parentModelType reflect.Type,
+	incomingParentIDs map[string]interface{}, // IDs from all ancestors
 ) error {
 	for relationName, relInfo := range relationFields {
 		relationValue, exists := relationData[relationName]
@@ -293,7 +321,7 @@ func (p *NestedCUDProcessor) processChildRelations(
 		// Get the related model
 		field, found := parentModelType.FieldByName(relInfo.FieldName)
 		if !found {
-			logger.Warn("Field %s not found in model", relInfo.FieldName)
+			logger.Error("Field %s not found in model type %v for relation %s", relInfo.FieldName, parentModelType, relationName)
 			continue
 		}
 
@@ -313,20 +341,89 @@ func (p *NestedCUDProcessor) processChildRelations(
 		relatedTableName := p.getTableNameForModel(relatedModel, relInfo.JSONName)
 
 		// Prepare parent IDs for foreign key injection
+		// Start by copying all incoming parent IDs (from ancestors)
 		parentIDs := make(map[string]interface{})
-		if relInfo.ForeignKey != "" {
+		for k, v := range incomingParentIDs {
+			parentIDs[k] = v
+		}
+		logger.Debug("Inherited %d parent IDs from ancestors: %+v", len(incomingParentIDs), incomingParentIDs)
+
+		// Add the current parent's primary key to the parentIDs map
+		// This ensures nested children have access to all ancestor IDs
+		if parentID != nil && parentModelType != nil {
+			// Get the parent model's primary key field name
+			parentPKFieldName := reflection.GetPrimaryKeyName(parentModelType)
+			if parentPKFieldName != "" {
+				// Get the JSON name for the primary key field
+				parentPKJSONName := reflection.GetJSONNameForField(parentModelType, parentPKFieldName)
+				baseName := ""
+				if len(parentPKJSONName) > 1 {
+					baseName = parentPKJSONName
+				} else {
+					// Add parent's PK to the map using the base model name
+					baseName = strings.TrimSuffix(parentPKFieldName, "ID")
+					baseName = strings.TrimSuffix(strings.ToLower(baseName), "_id")
+					if baseName == "" {
+						baseName = "parent"
+					}
+				}
+
+				parentIDs[baseName] = parentID
+				logger.Debug("Added current parent PK to parentIDs map: %s=%v (from field %s)", baseName, parentID, parentPKFieldName)
+			}
+		}
+
+		// Also add the foreign key reference if specified
+		if relInfo.ForeignKey != "" && parentID != nil {
 			// Extract the base name from foreign key (e.g., "DepartmentID" -> "Department")
 			baseName := strings.TrimSuffix(relInfo.ForeignKey, "ID")
 			baseName = strings.TrimSuffix(strings.ToLower(baseName), "_id")
-			parentIDs[baseName] = parentID
+			// Only add if different from what we already added
+			if _, exists := parentIDs[baseName]; !exists {
+				parentIDs[baseName] = parentID
+				logger.Debug("Added foreign key to parentIDs map: %s=%v (from FK %s)", baseName, parentID, relInfo.ForeignKey)
+			}
 		}
 
+		logger.Debug("Final parentIDs map for relation %s: %+v", relationName, parentIDs)
+
+		// Determine which field name to use for setting parent ID in child data
+		// Priority: Use foreign key field name if specified
+		var foreignKeyFieldName string
+		if relInfo.ForeignKey != "" {
+			// Get the JSON name for the foreign key field in the child model
+			foreignKeyFieldName = reflection.GetJSONNameForField(relatedModelType, relInfo.ForeignKey)
+			if foreignKeyFieldName == "" {
+				// Fallback to lowercase field name
+				foreignKeyFieldName = strings.ToLower(relInfo.ForeignKey)
+			}
+			logger.Debug("Using foreign key field for direct assignment: %s (from FK %s)", foreignKeyFieldName, relInfo.ForeignKey)
+		}
+
+		// Get the primary key name for the child model to avoid overwriting it in recursive relationships
+		childPKName := reflection.GetPrimaryKeyName(relatedModel)
+		childPKFieldName := reflection.GetJSONNameForField(relatedModelType, childPKName)
+		if childPKFieldName == "" {
+			childPKFieldName = strings.ToLower(childPKName)
+		}
+
+		logger.Debug("Processing relation with foreignKeyField=%s, childPK=%s", foreignKeyFieldName, childPKFieldName)
+
 		// Process based on relation type and data structure
 		switch v := relationValue.(type) {
 		case map[string]interface{}:
-			// Single related object
+			// Single related object - directly set foreign key if specified
+			// IMPORTANT: In recursive relationships, don't overwrite the primary key
+			if parentID != nil && foreignKeyFieldName != "" && foreignKeyFieldName != childPKFieldName {
+				v[foreignKeyFieldName] = parentID
+				logger.Debug("Set foreign key in single relation: %s=%v", foreignKeyFieldName, parentID)
+			} else if foreignKeyFieldName == childPKFieldName {
+				logger.Debug("Skipping foreign key assignment - same as primary key (recursive relationship): %s", foreignKeyFieldName)
+			}
 			_, err := p.ProcessNestedCUD(ctx, operation, v, relatedModel, parentIDs, relatedTableName)
 			if err != nil {
+				logger.Error("Failed to process single relation: name=%s, table=%s, operation=%s, parentID=%v, data=%+v, error=%v",
+					relationName, relatedTableName, operation, parentID, v, err)
 				return fmt.Errorf("failed to process relation %s: %w", relationName, err)
 			}
 
@@ -334,24 +431,46 @@ func (p *NestedCUDProcessor) processChildRelations(
 			// Multiple related objects
 			for i, item := range v {
 				if itemMap, ok := item.(map[string]interface{}); ok {
+					// Directly set foreign key if specified
+					// IMPORTANT: In recursive relationships, don't overwrite the primary key
+					if parentID != nil && foreignKeyFieldName != "" && foreignKeyFieldName != childPKFieldName {
+						itemMap[foreignKeyFieldName] = parentID
+						logger.Debug("Set foreign key in relation array[%d]: %s=%v", i, foreignKeyFieldName, parentID)
+					} else if foreignKeyFieldName == childPKFieldName {
+						logger.Debug("Skipping foreign key assignment in array[%d] - same as primary key (recursive relationship): %s", i, foreignKeyFieldName)
+					}
 					_, err := p.ProcessNestedCUD(ctx, operation, itemMap, relatedModel, parentIDs, relatedTableName)
 					if err != nil {
+						logger.Error("Failed to process relation array item: name=%s[%d], table=%s, operation=%s, parentID=%v, data=%+v, error=%v",
+							relationName, i, relatedTableName, operation, parentID, itemMap, err)
 						return fmt.Errorf("failed to process relation %s[%d]: %w", relationName, i, err)
 					}
+				} else {
+					logger.Warn("Relation array item is not a map: name=%s[%d], type=%T", relationName, i, item)
 				}
 			}
 
 		case []map[string]interface{}:
 			// Multiple related objects (typed slice)
 			for i, itemMap := range v {
+				// Directly set foreign key if specified
+				// IMPORTANT: In recursive relationships, don't overwrite the primary key
+				if parentID != nil && foreignKeyFieldName != "" && foreignKeyFieldName != childPKFieldName {
+					itemMap[foreignKeyFieldName] = parentID
+					logger.Debug("Set foreign key in relation typed array[%d]: %s=%v", i, foreignKeyFieldName, parentID)
+				} else if foreignKeyFieldName == childPKFieldName {
+					logger.Debug("Skipping foreign key assignment in typed array[%d] - same as primary key (recursive relationship): %s", i, foreignKeyFieldName)
+				}
 				_, err := p.ProcessNestedCUD(ctx, operation, itemMap, relatedModel, parentIDs, relatedTableName)
 				if err != nil {
+					logger.Error("Failed to process relation typed array item: name=%s[%d], table=%s, operation=%s, parentID=%v, data=%+v, error=%v",
+						relationName, i, relatedTableName, operation, parentID, itemMap, err)
 					return fmt.Errorf("failed to process relation %s[%d]: %w", relationName, i, err)
 				}
 			}
 
 		default:
-			logger.Warn("Unsupported relation data type for %s: %T", relationName, relationValue)
+			logger.Error("Unsupported relation data type: name=%s, type=%T, value=%+v", relationName, relationValue, relationValue)
 		}
 	}
 

pkg/common/recursive_crud_test.go

@@ -0,0 +1,720 @@
+package common
+
+import (
+	"context"
+	"reflect"
+	"testing"
+
+	"github.com/bitechdev/ResolveSpec/pkg/reflection"
+)
+
+// Mock Database for testing
+type mockDatabase struct {
+	insertCalls []map[string]interface{}
+	updateCalls []map[string]interface{}
+	deleteCalls []interface{}
+	lastID      int64
+}
+
+func newMockDatabase() *mockDatabase {
+	return &mockDatabase{
+		insertCalls: make([]map[string]interface{}, 0),
+		updateCalls: make([]map[string]interface{}, 0),
+		deleteCalls: make([]interface{}, 0),
+		lastID:      1,
+	}
+}
+
+func (m *mockDatabase) NewSelect() SelectQuery                       { return &mockSelectQuery{} }
+func (m *mockDatabase) NewInsert() InsertQuery                       { return &mockInsertQuery{db: m} }
+func (m *mockDatabase) NewUpdate() UpdateQuery                       { return &mockUpdateQuery{db: m} }
+func (m *mockDatabase) NewDelete() DeleteQuery                       { return &mockDeleteQuery{db: m} }
+func (m *mockDatabase) RunInTransaction(ctx context.Context, fn func(Database) error) error {
+	return fn(m)
+}
+func (m *mockDatabase) Exec(ctx context.Context, query string, args ...interface{}) (Result, error) {
+	return &mockResult{rowsAffected: 1}, nil
+}
+func (m *mockDatabase) Query(ctx context.Context, dest interface{}, query string, args ...interface{}) error {
+	return nil
+}
+func (m *mockDatabase) BeginTx(ctx context.Context) (Database, error) {
+	return m, nil
+}
+func (m *mockDatabase) CommitTx(ctx context.Context) error {
+	return nil
+}
+func (m *mockDatabase) RollbackTx(ctx context.Context) error {
+	return nil
+}
+func (m *mockDatabase) GetUnderlyingDB() interface{} {
+	return nil
+}
+
+// Mock SelectQuery
+type mockSelectQuery struct{}
+
+func (m *mockSelectQuery) Model(model interface{}) SelectQuery                { return m }
+func (m *mockSelectQuery) Table(name string) SelectQuery                      { return m }
+func (m *mockSelectQuery) Column(columns ...string) SelectQuery               { return m }
+func (m *mockSelectQuery) ColumnExpr(query string, args ...interface{}) SelectQuery { return m }
+func (m *mockSelectQuery) Where(condition string, args ...interface{}) SelectQuery { return m }
+func (m *mockSelectQuery) WhereOr(query string, args ...interface{}) SelectQuery { return m }
+func (m *mockSelectQuery) Join(query string, args ...interface{}) SelectQuery { return m }
+func (m *mockSelectQuery) LeftJoin(query string, args ...interface{}) SelectQuery { return m }
+func (m *mockSelectQuery) Preload(relation string, conditions ...interface{}) SelectQuery { return m }
+func (m *mockSelectQuery) PreloadRelation(relation string, apply ...func(SelectQuery) SelectQuery) SelectQuery { return m }
+func (m *mockSelectQuery) JoinRelation(relation string, apply ...func(SelectQuery) SelectQuery) SelectQuery { return m }
+func (m *mockSelectQuery) Order(order string) SelectQuery                     { return m }
+func (m *mockSelectQuery) OrderExpr(order string, args ...interface{}) SelectQuery { return m }
+func (m *mockSelectQuery) Limit(n int) SelectQuery                            { return m }
+func (m *mockSelectQuery) Offset(n int) SelectQuery                           { return m }
+func (m *mockSelectQuery) Group(group string) SelectQuery                     { return m }
+func (m *mockSelectQuery) Having(condition string, args ...interface{}) SelectQuery { return m }
+func (m *mockSelectQuery) Scan(ctx context.Context, dest interface{}) error  { return nil }
+func (m *mockSelectQuery) ScanModel(ctx context.Context) error               { return nil }
+func (m *mockSelectQuery) Count(ctx context.Context) (int, error)            { return 0, nil }
+func (m *mockSelectQuery) Exists(ctx context.Context) (bool, error)          { return false, nil }
+
+// Mock InsertQuery
+type mockInsertQuery struct {
+	db     *mockDatabase
+	table  string
+	values map[string]interface{}
+}
+
+func (m *mockInsertQuery) Model(model interface{}) InsertQuery { return m }
+func (m *mockInsertQuery) Table(name string) InsertQuery {
+	m.table = name
+	return m
+}
+func (m *mockInsertQuery) Value(column string, value interface{}) InsertQuery {
+	if m.values == nil {
+		m.values = make(map[string]interface{})
+	}
+	m.values[column] = value
+	return m
+}
+func (m *mockInsertQuery) OnConflict(action string) InsertQuery { return m }
+func (m *mockInsertQuery) Returning(columns ...string) InsertQuery { return m }
+func (m *mockInsertQuery) Exec(ctx context.Context) (Result, error) {
+	// Record the insert call
+	m.db.insertCalls = append(m.db.insertCalls, m.values)
+	m.db.lastID++
+	return &mockResult{lastID: m.db.lastID, rowsAffected: 1}, nil
+}
+
+// Mock UpdateQuery
+type mockUpdateQuery struct {
+	db        *mockDatabase
+	table     string
+	setValues map[string]interface{}
+}
+
+func (m *mockUpdateQuery) Model(model interface{}) UpdateQuery { return m }
+func (m *mockUpdateQuery) Table(name string) UpdateQuery {
+	m.table = name
+	return m
+}
+func (m *mockUpdateQuery) Set(column string, value interface{}) UpdateQuery { return m }
+func (m *mockUpdateQuery) SetMap(values map[string]interface{}) UpdateQuery {
+	m.setValues = values
+	return m
+}
+func (m *mockUpdateQuery) Where(condition string, args ...interface{}) UpdateQuery { return m }
+func (m *mockUpdateQuery) Returning(columns ...string) UpdateQuery { return m }
+func (m *mockUpdateQuery) Exec(ctx context.Context) (Result, error) {
+	// Record the update call
+	m.db.updateCalls = append(m.db.updateCalls, m.setValues)
+	return &mockResult{rowsAffected: 1}, nil
+}
+
+// Mock DeleteQuery
+type mockDeleteQuery struct {
+	db    *mockDatabase
+	table string
+}
+
+func (m *mockDeleteQuery) Model(model interface{}) DeleteQuery { return m }
+func (m *mockDeleteQuery) Table(name string) DeleteQuery {
+	m.table = name
+	return m
+}
+func (m *mockDeleteQuery) Where(condition string, args ...interface{}) DeleteQuery { return m }
+func (m *mockDeleteQuery) Exec(ctx context.Context) (Result, error) {
+	// Record the delete call
+	m.db.deleteCalls = append(m.db.deleteCalls, m.table)
+	return &mockResult{rowsAffected: 1}, nil
+}
+
+// Mock Result
+type mockResult struct {
+	lastID       int64
+	rowsAffected int64
+}
+
+func (m *mockResult) LastInsertId() (int64, error) { return m.lastID, nil }
+func (m *mockResult) RowsAffected() int64          { return m.rowsAffected }
+
+// Mock ModelRegistry
+type mockModelRegistry struct{}
+
+func (m *mockModelRegistry) GetModel(name string) (interface{}, error) { return nil, nil }
+func (m *mockModelRegistry) GetModelByEntity(schema, entity string) (interface{}, error) { return nil, nil }
+func (m *mockModelRegistry) RegisterModel(name string, model interface{}) error { return nil }
+func (m *mockModelRegistry) GetAllModels() map[string]interface{} { return make(map[string]interface{}) }
+
+// Mock RelationshipInfoProvider
+type mockRelationshipProvider struct {
+	relationships map[string]*RelationshipInfo
+}
+
+func newMockRelationshipProvider() *mockRelationshipProvider {
+	return &mockRelationshipProvider{
+		relationships: make(map[string]*RelationshipInfo),
+	}
+}
+
+func (m *mockRelationshipProvider) GetRelationshipInfo(modelType reflect.Type, relationName string) *RelationshipInfo {
+	key := modelType.Name() + "." + relationName
+	return m.relationships[key]
+}
+
+func (m *mockRelationshipProvider) RegisterRelation(modelTypeName, relationName string, info *RelationshipInfo) {
+	key := modelTypeName + "." + relationName
+	m.relationships[key] = info
+}
+
+// Test Models
+type Department struct {
+	ID        int64        `json:"id" bun:"id,pk"`
+	Name      string       `json:"name"`
+	Employees []*Employee  `json:"employees,omitempty"`
+}
+
+func (d Department) TableName() string { return "departments" }
+func (d Department) GetIDName() string { return "ID" }
+
+type Employee struct {
+	ID           int64   `json:"id" bun:"id,pk"`
+	Name         string  `json:"name"`
+	DepartmentID int64   `json:"department_id"`
+	Tasks        []*Task `json:"tasks,omitempty"`
+}
+
+func (e Employee) TableName() string { return "employees" }
+func (e Employee) GetIDName() string { return "ID" }
+
+type Task struct {
+	ID         int64      `json:"id" bun:"id,pk"`
+	Title      string     `json:"title"`
+	EmployeeID int64      `json:"employee_id"`
+	Comments   []*Comment `json:"comments,omitempty"`
+}
+
+func (t Task) TableName() string { return "tasks" }
+func (t Task) GetIDName() string { return "ID" }
+
+type Comment struct {
+	ID      int64  `json:"id" bun:"id,pk"`
+	Text    string `json:"text"`
+	TaskID  int64  `json:"task_id"`
+}
+
+func (c Comment) TableName() string { return "comments" }
+func (c Comment) GetIDName() string { return "ID" }
+
+// Test Cases
+
+func TestProcessNestedCUD_SingleLevelInsert(t *testing.T) {
+	db := newMockDatabase()
+	registry := &mockModelRegistry{}
+	relProvider := newMockRelationshipProvider()
+
+	// Register Department -> Employees relationship
+	relProvider.RegisterRelation("Department", "employees", &RelationshipInfo{
+		FieldName:    "Employees",
+		JSONName:     "employees",
+		RelationType: "has_many",
+		ForeignKey:   "DepartmentID",
+		RelatedModel: Employee{},
+	})
+
+	processor := NewNestedCUDProcessor(db, registry, relProvider)
+
+	data := map[string]interface{}{
+		"name": "Engineering",
+		"employees": []interface{}{
+			map[string]interface{}{
+				"name": "John Doe",
+			},
+			map[string]interface{}{
+				"name": "Jane Smith",
+			},
+		},
+	}
+
+	result, err := processor.ProcessNestedCUD(
+		context.Background(),
+		"insert",
+		data,
+		Department{},
+		nil,
+		"departments",
+	)
+
+	if err != nil {
+		t.Fatalf("ProcessNestedCUD failed: %v", err)
+	}
+
+	if result.ID == nil {
+		t.Error("Expected result.ID to be set")
+	}
+
+	// Verify department was inserted
+	if len(db.insertCalls) != 3 {
+		t.Errorf("Expected 3 insert calls (1 dept + 2 employees), got %d", len(db.insertCalls))
+	}
+
+	// Verify first insert is department
+	if db.insertCalls[0]["name"] != "Engineering" {
+		t.Errorf("Expected department name 'Engineering', got %v", db.insertCalls[0]["name"])
+	}
+
+	// Verify employees were inserted with foreign key
+	if db.insertCalls[1]["department_id"] == nil {
+		t.Error("Expected employee to have department_id set")
+	}
+	if db.insertCalls[2]["department_id"] == nil {
+		t.Error("Expected employee to have department_id set")
+	}
+}
+
+func TestProcessNestedCUD_MultiLevelInsert(t *testing.T) {
+	db := newMockDatabase()
+	registry := &mockModelRegistry{}
+	relProvider := newMockRelationshipProvider()
+
+	// Register relationships
+	relProvider.RegisterRelation("Department", "employees", &RelationshipInfo{
+		FieldName:    "Employees",
+		JSONName:     "employees",
+		RelationType: "has_many",
+		ForeignKey:   "DepartmentID",
+		RelatedModel: Employee{},
+	})
+
+	relProvider.RegisterRelation("Employee", "tasks", &RelationshipInfo{
+		FieldName:    "Tasks",
+		JSONName:     "tasks",
+		RelationType: "has_many",
+		ForeignKey:   "EmployeeID",
+		RelatedModel: Task{},
+	})
+
+	processor := NewNestedCUDProcessor(db, registry, relProvider)
+
+	data := map[string]interface{}{
+		"name": "Engineering",
+		"employees": []interface{}{
+			map[string]interface{}{
+				"name": "John Doe",
+				"tasks": []interface{}{
+					map[string]interface{}{
+						"title": "Task 1",
+					},
+					map[string]interface{}{
+						"title": "Task 2",
+					},
+				},
+			},
+		},
+	}
+
+	result, err := processor.ProcessNestedCUD(
+		context.Background(),
+		"insert",
+		data,
+		Department{},
+		nil,
+		"departments",
+	)
+
+	if err != nil {
+		t.Fatalf("ProcessNestedCUD failed: %v", err)
+	}
+
+	if result.ID == nil {
+		t.Error("Expected result.ID to be set")
+	}
+
+	// Verify: 1 dept + 1 employee + 2 tasks = 4 inserts
+	if len(db.insertCalls) != 4 {
+		t.Errorf("Expected 4 insert calls, got %d", len(db.insertCalls))
+	}
+
+	// Verify department
+	if db.insertCalls[0]["name"] != "Engineering" {
+		t.Errorf("Expected department name 'Engineering', got %v", db.insertCalls[0]["name"])
+	}
+
+	// Verify employee has department_id
+	if db.insertCalls[1]["department_id"] == nil {
+		t.Error("Expected employee to have department_id set")
+	}
+
+	// Verify tasks have employee_id
+	if db.insertCalls[2]["employee_id"] == nil {
+		t.Error("Expected task to have employee_id set")
+	}
+	if db.insertCalls[3]["employee_id"] == nil {
+		t.Error("Expected task to have employee_id set")
+	}
+}
+
+func TestProcessNestedCUD_RequestFieldOverride(t *testing.T) {
+	db := newMockDatabase()
+	registry := &mockModelRegistry{}
+	relProvider := newMockRelationshipProvider()
+
+	relProvider.RegisterRelation("Department", "employees", &RelationshipInfo{
+		FieldName:    "Employees",
+		JSONName:     "employees",
+		RelationType: "has_many",
+		ForeignKey:   "DepartmentID",
+		RelatedModel: Employee{},
+	})
+
+	processor := NewNestedCUDProcessor(db, registry, relProvider)
+
+	data := map[string]interface{}{
+		"name": "Engineering",
+		"employees": []interface{}{
+			map[string]interface{}{
+				"_request": "update",
+				"ID":       int64(10), // Use capital ID to match struct field
+				"name":     "John Updated",
+			},
+		},
+	}
+
+	_, err := processor.ProcessNestedCUD(
+		context.Background(),
+		"insert",
+		data,
+		Department{},
+		nil,
+		"departments",
+	)
+
+	if err != nil {
+		t.Fatalf("ProcessNestedCUD failed: %v", err)
+	}
+
+	// Verify department was inserted (1 insert)
+	// Employee should be updated (1 update)
+	if len(db.insertCalls) != 1 {
+		t.Errorf("Expected 1 insert call for department, got %d", len(db.insertCalls))
+	}
+
+	if len(db.updateCalls) != 1 {
+		t.Errorf("Expected 1 update call for employee, got %d", len(db.updateCalls))
+	}
+
+	// Verify update data
+	if db.updateCalls[0]["name"] != "John Updated" {
+		t.Errorf("Expected employee name 'John Updated', got %v", db.updateCalls[0]["name"])
+	}
+}
+
+func TestProcessNestedCUD_SkipInsertWhenOnlyRequestField(t *testing.T) {
+	db := newMockDatabase()
+	registry := &mockModelRegistry{}
+	relProvider := newMockRelationshipProvider()
+
+	relProvider.RegisterRelation("Department", "employees", &RelationshipInfo{
+		FieldName:    "Employees",
+		JSONName:     "employees",
+		RelationType: "has_many",
+		ForeignKey:   "DepartmentID",
+		RelatedModel: Employee{},
+	})
+
+	processor := NewNestedCUDProcessor(db, registry, relProvider)
+
+	// Data with only _request field for nested employee
+	data := map[string]interface{}{
+		"name": "Engineering",
+		"employees": []interface{}{
+			map[string]interface{}{
+				"_request": "insert",
+				// No other fields besides _request
+				// Note: Foreign key will be injected, so employee WILL be inserted
+			},
+		},
+	}
+
+	_, err := processor.ProcessNestedCUD(
+		context.Background(),
+		"insert",
+		data,
+		Department{},
+		nil,
+		"departments",
+	)
+
+	if err != nil {
+		t.Fatalf("ProcessNestedCUD failed: %v", err)
+	}
+
+	// Department + Employee (with injected FK) = 2 inserts
+	if len(db.insertCalls) != 2 {
+		t.Errorf("Expected 2 insert calls (department + employee with FK), got %d", len(db.insertCalls))
+	}
+
+	if db.insertCalls[0]["name"] != "Engineering" {
+		t.Errorf("Expected department name 'Engineering', got %v", db.insertCalls[0]["name"])
+	}
+
+	// Verify employee has foreign key
+	if db.insertCalls[1]["department_id"] == nil {
+		t.Error("Expected employee to have department_id injected")
+	}
+}
+
+func TestProcessNestedCUD_Update(t *testing.T) {
+	db := newMockDatabase()
+	registry := &mockModelRegistry{}
+	relProvider := newMockRelationshipProvider()
+
+	relProvider.RegisterRelation("Department", "employees", &RelationshipInfo{
+		FieldName:    "Employees",
+		JSONName:     "employees",
+		RelationType: "has_many",
+		ForeignKey:   "DepartmentID",
+		RelatedModel: Employee{},
+	})
+
+	processor := NewNestedCUDProcessor(db, registry, relProvider)
+
+	data := map[string]interface{}{
+		"ID":   int64(1), // Use capital ID to match struct field
+		"name": "Engineering Updated",
+		"employees": []interface{}{
+			map[string]interface{}{
+				"_request": "insert",
+				"name":     "New Employee",
+			},
+		},
+	}
+
+	result, err := processor.ProcessNestedCUD(
+		context.Background(),
+		"update",
+		data,
+		Department{},
+		nil,
+		"departments",
+	)
+
+	if err != nil {
+		t.Fatalf("ProcessNestedCUD failed: %v", err)
+	}
+
+	if result.ID != int64(1) {
+		t.Errorf("Expected result.ID to be 1, got %v", result.ID)
+	}
+
+	// Verify department was updated
+	if len(db.updateCalls) != 1 {
+		t.Errorf("Expected 1 update call, got %d", len(db.updateCalls))
+	}
+
+	// Verify new employee was inserted
+	if len(db.insertCalls) != 1 {
+		t.Errorf("Expected 1 insert call for new employee, got %d", len(db.insertCalls))
+	}
+}
+
+func TestProcessNestedCUD_Delete(t *testing.T) {
+	db := newMockDatabase()
+	registry := &mockModelRegistry{}
+	relProvider := newMockRelationshipProvider()
+
+	relProvider.RegisterRelation("Department", "employees", &RelationshipInfo{
+		FieldName:    "Employees",
+		JSONName:     "employees",
+		RelationType: "has_many",
+		ForeignKey:   "DepartmentID",
+		RelatedModel: Employee{},
+	})
+
+	processor := NewNestedCUDProcessor(db, registry, relProvider)
+
+	data := map[string]interface{}{
+		"ID": int64(1), // Use capital ID to match struct field
+		"employees": []interface{}{
+			map[string]interface{}{
+				"_request": "delete",
+				"ID":       int64(10), // Use capital ID
+			},
+			map[string]interface{}{
+				"_request": "delete",
+				"ID":       int64(11), // Use capital ID
+			},
+		},
+	}
+
+	_, err := processor.ProcessNestedCUD(
+		context.Background(),
+		"delete",
+		data,
+		Department{},
+		nil,
+		"departments",
+	)
+
+	if err != nil {
+		t.Fatalf("ProcessNestedCUD failed: %v", err)
+	}
+
+	// Verify employees were deleted first, then department
+	// 2 employees + 1 department = 3 deletes
+	if len(db.deleteCalls) != 3 {
+		t.Errorf("Expected 3 delete calls, got %d", len(db.deleteCalls))
+	}
+}
+
+func TestProcessNestedCUD_ParentIDPropagation(t *testing.T) {
+	db := newMockDatabase()
+	registry := &mockModelRegistry{}
+	relProvider := newMockRelationshipProvider()
+
+	// Register 3-level relationships
+	relProvider.RegisterRelation("Department", "employees", &RelationshipInfo{
+		FieldName:    "Employees",
+		JSONName:     "employees",
+		RelationType: "has_many",
+		ForeignKey:   "DepartmentID",
+		RelatedModel: Employee{},
+	})
+
+	relProvider.RegisterRelation("Employee", "tasks", &RelationshipInfo{
+		FieldName:    "Tasks",
+		JSONName:     "tasks",
+		RelationType: "has_many",
+		ForeignKey:   "EmployeeID",
+		RelatedModel: Task{},
+	})
+
+	relProvider.RegisterRelation("Task", "comments", &RelationshipInfo{
+		FieldName:    "Comments",
+		JSONName:     "comments",
+		RelationType: "has_many",
+		ForeignKey:   "TaskID",
+		RelatedModel: Comment{},
+	})
+
+	processor := NewNestedCUDProcessor(db, registry, relProvider)
+
+	data := map[string]interface{}{
+		"name": "Engineering",
+		"employees": []interface{}{
+			map[string]interface{}{
+				"name": "John",
+				"tasks": []interface{}{
+					map[string]interface{}{
+						"title": "Task 1",
+						"comments": []interface{}{
+							map[string]interface{}{
+								"text": "Great work!",
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	_, err := processor.ProcessNestedCUD(
+		context.Background(),
+		"insert",
+		data,
+		Department{},
+		nil,
+		"departments",
+	)
+
+	if err != nil {
+		t.Fatalf("ProcessNestedCUD failed: %v", err)
+	}
+
+	// Verify: 1 dept + 1 employee + 1 task + 1 comment = 4 inserts
+	if len(db.insertCalls) != 4 {
+		t.Errorf("Expected 4 insert calls, got %d", len(db.insertCalls))
+	}
+
+	// Verify department
+	if db.insertCalls[0]["name"] != "Engineering" {
+		t.Error("Expected department to be inserted first")
+	}
+
+	// Verify employee has department_id
+	if db.insertCalls[1]["department_id"] == nil {
+		t.Error("Expected employee to have department_id")
+	}
+
+	// Verify task has employee_id
+	if db.insertCalls[2]["employee_id"] == nil {
+		t.Error("Expected task to have employee_id")
+	}
+
+	// Verify comment has task_id
+	if db.insertCalls[3]["task_id"] == nil {
+		t.Error("Expected comment to have task_id")
+	}
+}
+
+func TestInjectForeignKeys(t *testing.T) {
+	db := newMockDatabase()
+	registry := &mockModelRegistry{}
+	relProvider := newMockRelationshipProvider()
+
+	processor := NewNestedCUDProcessor(db, registry, relProvider)
+
+	data := map[string]interface{}{
+		"name": "John",
+	}
+
+	parentIDs := map[string]interface{}{
+		"department": int64(5),
+	}
+
+	modelType := reflect.TypeOf(Employee{})
+
+	processor.injectForeignKeys(data, modelType, parentIDs)
+
+	// Should inject department_id based on the "department" key in parentIDs
+	if data["department_id"] == nil {
+		t.Error("Expected department_id to be injected")
+	}
+
+	if data["department_id"] != int64(5) {
+		t.Errorf("Expected department_id to be 5, got %v", data["department_id"])
+	}
+}
+
+func TestGetPrimaryKeyName(t *testing.T) {
+	dept := Department{}
+	pkName := reflection.GetPrimaryKeyName(dept)
+
+	if pkName != "ID" {
+		t.Errorf("Expected primary key name 'ID', got '%s'", pkName)
+	}
+
+	// Test with pointer
+	pkName2 := reflection.GetPrimaryKeyName(&dept)
+	if pkName2 != "ID" {
+		t.Errorf("Expected primary key name 'ID' from pointer, got '%s'", pkName2)
+	}
+}

pkg/reflection/helpers.go

@@ -1,6 +1,9 @@
 package reflection
 
-import "reflect"
+import (
+	"reflect"
+	"strings"
+)
 
 func Len(v any) int {
 	val := reflect.ValueOf(v)
@@ -64,3 +67,41 @@ func GetPointerElement(v reflect.Type) reflect.Type {
 	}
 	return v
 }
+
+// GetJSONNameForField gets the JSON tag name for a struct field.
+// Returns the JSON field name from the json struct tag, or an empty string if not found.
+// Handles the "json" tag format: "name", "name,omitempty", etc.
+func GetJSONNameForField(modelType reflect.Type, fieldName string) string {
+	if modelType == nil {
+		return ""
+	}
+
+	// Handle pointer types
+	if modelType.Kind() == reflect.Ptr {
+		modelType = modelType.Elem()
+	}
+
+	if modelType.Kind() != reflect.Struct {
+		return ""
+	}
+
+	// Find the field
+	field, found := modelType.FieldByName(fieldName)
+	if !found {
+		return ""
+	}
+
+	// Get the JSON tag
+	jsonTag := field.Tag.Get("json")
+	if jsonTag == "" {
+		return ""
+	}
+
+	// Parse the tag (format: "name,omitempty" or just "name")
+	parts := strings.Split(jsonTag, ",")
+	if len(parts) > 0 && parts[0] != "" && parts[0] != "-" {
+		return parts[0]
+	}
+
+	return ""
+}

pkg/restheadspec/handler.go

@@ -1794,10 +1794,46 @@ func (h *Handler) processChildRelationsForField(
 		parentIDs[baseName] = parentID
 	}
 
+	// Determine which field name to use for setting parent ID in child data
+	// Priority: Use foreign key field name if specified, otherwise use parent's PK name
+	var foreignKeyFieldName string
+	if relInfo.ForeignKey != "" {
+		// Get the JSON name for the foreign key field in the child model
+		foreignKeyFieldName = reflection.GetJSONNameForField(relatedModelType, relInfo.ForeignKey)
+		if foreignKeyFieldName == "" {
+			// Fallback to lowercase field name
+			foreignKeyFieldName = strings.ToLower(relInfo.ForeignKey)
+		}
+	} else {
+		// Fallback: use parent's primary key name
+		parentPKName := reflection.GetPrimaryKeyName(parentModelType)
+		foreignKeyFieldName = reflection.GetJSONNameForField(parentModelType, parentPKName)
+		if foreignKeyFieldName == "" {
+			foreignKeyFieldName = strings.ToLower(parentPKName)
+		}
+	}
+
+	// Get the primary key name for the child model to avoid overwriting it in recursive relationships
+	childPKName := reflection.GetPrimaryKeyName(relatedModel)
+	childPKFieldName := reflection.GetJSONNameForField(relatedModelType, childPKName)
+	if childPKFieldName == "" {
+		childPKFieldName = strings.ToLower(childPKName)
+	}
+
+	logger.Debug("Setting parent ID in child data: foreignKeyField=%s, parentID=%v, relForeignKey=%s, childPK=%s",
+		foreignKeyFieldName, parentID, relInfo.ForeignKey, childPKFieldName)
+
 	// Process based on relation type and data structure
 	switch v := relationValue.(type) {
 	case map[string]interface{}:
-		// Single related object
+		// Single related object - add parent ID to foreign key field
+		// IMPORTANT: In recursive relationships, don't overwrite the primary key
+		if parentID != nil && foreignKeyFieldName != "" && foreignKeyFieldName != childPKFieldName {
+			v[foreignKeyFieldName] = parentID
+			logger.Debug("Set foreign key in single relation: %s=%v", foreignKeyFieldName, parentID)
+		} else if foreignKeyFieldName == childPKFieldName {
+			logger.Debug("Skipping foreign key assignment - same as primary key (recursive relationship): %s", foreignKeyFieldName)
+		}
 		_, err := processor.ProcessNestedCUD(ctx, operation, v, relatedModel, parentIDs, relatedTableName)
 		if err != nil {
 			return fmt.Errorf("failed to process single relation: %w", err)
@@ -1807,6 +1843,14 @@ func (h *Handler) processChildRelationsForField(
 		// Multiple related objects
 		for i, item := range v {
 			if itemMap, ok := item.(map[string]interface{}); ok {
+				// Add parent ID to foreign key field
+				// IMPORTANT: In recursive relationships, don't overwrite the primary key
+				if parentID != nil && foreignKeyFieldName != "" && foreignKeyFieldName != childPKFieldName {
+					itemMap[foreignKeyFieldName] = parentID
+					logger.Debug("Set foreign key in relation array[%d]: %s=%v", i, foreignKeyFieldName, parentID)
+				} else if foreignKeyFieldName == childPKFieldName {
+					logger.Debug("Skipping foreign key assignment in array[%d] - same as primary key (recursive relationship): %s", i, foreignKeyFieldName)
+				}
 				_, err := processor.ProcessNestedCUD(ctx, operation, itemMap, relatedModel, parentIDs, relatedTableName)
 				if err != nil {
 					return fmt.Errorf("failed to process relation item %d: %w", i, err)
@@ -1817,6 +1861,14 @@ func (h *Handler) processChildRelationsForField(
 	case []map[string]interface{}:
 		// Multiple related objects (typed slice)
 		for i, itemMap := range v {
+			// Add parent ID to foreign key field
+			// IMPORTANT: In recursive relationships, don't overwrite the primary key
+			if parentID != nil && foreignKeyFieldName != "" && foreignKeyFieldName != childPKFieldName {
+				itemMap[foreignKeyFieldName] = parentID
+				logger.Debug("Set foreign key in relation typed array[%d]: %s=%v", i, foreignKeyFieldName, parentID)
+			} else if foreignKeyFieldName == childPKFieldName {
+				logger.Debug("Skipping foreign key assignment in typed array[%d] - same as primary key (recursive relationship): %s", i, foreignKeyFieldName)
+			}
 			_, err := processor.ProcessNestedCUD(ctx, operation, itemMap, relatedModel, parentIDs, relatedTableName)
 			if err != nil {
 				return fmt.Errorf("failed to process relation item %d: %w", i, err)