Preload fixes

pkg/common/adapters/database/gorm.go

@@ -204,7 +204,7 @@ func (g *GormSelectQuery) PreloadRelation(relation string, apply ...func(common.
 		}
 
 		wrapper := &GormSelectQuery{
-			db: g.db,
+			db: db,
 		}
 
 		current := common.SelectQuery(wrapper)

pkg/resolvespec/handler.go

@@ -1137,8 +1137,8 @@ func (h *Handler) applyPreloads(model interface{}, query common.SelectQuery, pre
 		// This requires a more sophisticated approach with callbacks or query builders
 		// Apply preloading
 
-		logger.Debug("Applying preload: %s", preload.Relation)
+		logger.Debug("Applying preload: %s", relationFieldName)
-		query = query.PreloadRelation(preload.Relation, func(sq common.SelectQuery) common.SelectQuery {
+		query = query.PreloadRelation(relationFieldName, func(sq common.SelectQuery) common.SelectQuery {
 			if len(preload.OmitColumns) > 0 {
 				allCols := reflection.GetModelColumns(model)
 				// Remove omitted columns
@@ -1158,7 +1158,28 @@ func (h *Handler) applyPreloads(model interface{}, query common.SelectQuery, pre
 			}
 
 			if len(preload.Columns) > 0 {
-				sq = sq.Column(preload.Columns...)
+				// Ensure foreign key is included in column selection for GORM to establish the relationship
+				columns := make([]string, len(preload.Columns))
+				copy(columns, preload.Columns)
+
+				// Add foreign key if not already present
+				if relInfo.foreignKey != "" {
+					// Convert struct field name (e.g., DepartmentID) to snake_case (e.g., department_id)
+					foreignKeyColumn := toSnakeCase(relInfo.foreignKey)
+
+					hasForeignKey := false
+					for _, col := range columns {
+						if col == foreignKeyColumn || col == relInfo.foreignKey {
+							hasForeignKey = true
+							break
+						}
+					}
+					if !hasForeignKey {
+						columns = append(columns, foreignKeyColumn)
+					}
+				}
+
+				sq = sq.Column(columns...)
 			}
 
 			if len(preload.Filters) > 0 {
@@ -1240,3 +1261,28 @@ func (h *Handler) extractTagValue(tag, key string) string {
 	}
 	return ""
 }
+
+// toSnakeCase converts a PascalCase or camelCase string to snake_case
+func toSnakeCase(s string) string {
+	var result strings.Builder
+	runes := []rune(s)
+
+	for i := 0; i < len(runes); i++ {
+		r := runes[i]
+
+		if i > 0 && r >= 'A' && r <= 'Z' {
+			// Check if previous character is lowercase or if next character is lowercase
+			prevIsLower := runes[i-1] >= 'a' && runes[i-1] <= 'z'
+			nextIsLower := i+1 < len(runes) && runes[i+1] >= 'a' && runes[i+1] <= 'z'
+
+			// Add underscore if this is the start of a new word
+			// (previous was lowercase OR this is followed by lowercase)
+			if prevIsLower || nextIsLower {
+				result.WriteByte('_')
+			}
+		}
+
+		result.WriteRune(r)
+	}
+	return strings.ToLower(result.String())
+}