Cache columeToIndexFieldMap (#131)

dbscan/dbscan.go

@@ -6,6 +6,7 @@ import (
 	"reflect"
 	"regexp"
 	"strings"
+	"sync"
 )
 
 // Rows is an abstract database rows that dbscan can iterate over and get the data from.
@@ -54,13 +55,16 @@ func SnakeCaseMapper(str string) string {
 
 // API is the core type in dbscan. It implements all the logic and exposes functionality available in the package.
 // With API type users can create a custom API instance and override default settings hence configure dbscan.
+// API should not be copied after first use.
 type API struct {
 	structTagKey          string
 	columnSeparator       string
 	fieldMapperFn         NameMapperFunc
 	scannableTypesOption  []interface{}
 	scannableTypesReflect []reflect.Type
 	allowUnknownColumns   bool
+	// columnToIndexFieldMapCache stores a map of reflect.Type -> map[string][]int
+	columnToIndexFieldMapCache sync.Map
 }
 
 // APIOption is a function type that changes API configuration.

dbscan/structref.go

@@ -12,6 +12,18 @@ type toTraverse struct {
 }
 
 func (api *API) getColumnToFieldIndexMap(structType reflect.Type) map[string][]int {
+	resultIface, ok := api.columnToIndexFieldMapCache.Load(structType)
+	if ok {
+		return resultIface.(map[string][]int)
+	}
+
+	result := api.buildColumnToFieldIndexMap(structType)
+	resultIface, _ = api.columnToIndexFieldMapCache.LoadOrStore(structType, result)
+	result = resultIface.(map[string][]int)
+	return result
+}
+
+func (api *API) buildColumnToFieldIndexMap(structType reflect.Type) map[string][]int {
 	result := make(map[string][]int, structType.NumField())
 	var queue []*toTraverse
 	queue = append(queue, &toTraverse{Type: structType, IndexPrefix: nil, ColumnPrefix: ""})