add get alias func

fieldmapper.go

@@ -1,6 +1,8 @@
 package sqlbuilder
 
 import (
+	"reflect"
+
 	"github.com/huandu/xstrings"
 )
 
@@ -13,8 +15,19 @@ var (
 	//
 	// Field mapper is called only once on a Struct when the Struct is used to create builder for the first time.
 	DefaultFieldMapper FieldMapperFunc
+
+	// DefaultGetAlias is the default alias and dbtag get func
+	DefaultGetAlias GetAliasFunc
 )
 
+func init() {
+	DefaultGetAlias = func(field *reflect.StructField) (alias string, dbtag string) {
+		dbtag = field.Tag.Get(DBTag)
+		alias = dbtag
+		return
+	}
+}
+
 // FieldMapperFunc is a func to map struct field names to column names,
 // which will be used in query as columns.
 type FieldMapperFunc func(name string) string
@@ -28,3 +41,6 @@ type FieldMapperFunc func(name string) string
 func SnakeCaseMapper(field string) string {
 	return xstrings.ToSnakeCase(field)
 }
+
+// GetAliasFunc is a func to get alias and dbtag
+type GetAliasFunc func(field *reflect.StructField) (alias string, dbtag string)

structfields.go

@@ -86,20 +86,17 @@ func (sfs *structFields) parse(t reflect.Type, mapper FieldMapperFunc, prefix st
 		}
 
 		// Parse DBTag.
-		dbtag := field.Tag.Get(DBTag)
+		alias, dbtag := DefaultGetAlias(&field)
 
-		if dbtag == "-" {
+		if alias == "-" {
 			continue
 		}
 
-		alias := dbtag
-
-		if dbtag == "" {
+		if alias == "" {
 			alias = field.Name
-		}
-
-		if mapper != nil {
-			alias = mapper(alias)
+			if mapper != nil {
+				alias = mapper(alias)
+			}
 		}
 
 		// Parse FieldOpt.