Decrement fork counter on gist/user delete

internal/models/gist.go

@@ -1,6 +1,7 @@
 package models
 
 import (
+	"gorm.io/gorm"
 	"time"
 )
 
@@ -41,6 +42,15 @@ type Commit struct {
 	Files     []File
 }
 
+func (g *Gist) BeforeDelete(tx *gorm.DB) error {
+	// Decrement fork counter if the gist was forked
+	err := tx.Model(&Gist{}).
+		Omit("updated_at").
+		Where("id = ?", g.ForkedID).
+		UpdateColumn("nb_forks", gorm.Expr("nb_forks - 1")).Error
+	return err
+}
+
 func GetGist(user string, gistUuid string) (*Gist, error) {
 	gist := new(Gist)
 	err := db.Preload("User").Preload("Forked.User").
@@ -141,10 +151,6 @@ func IncrementGistForkCount(gist *Gist) error {
 	return db.Model(&gist).Omit("updated_at").Update("nb_forks", gist.NbForks+1).Error
 }
 
-func DecrementGistForkCount(gist *Gist) error {
-	return db.Model(&gist).Omit("updated_at").Update("nb_forks", gist.NbForks-1).Error
-}
-
 func GetForkedGist(gist *Gist, user *User) (*Gist, error) {
 	fork := new(Gist)
 	err := db.Preload("User").