fix: use TurnOffAutoMigrate instead of NewAdapterWithoutAutoMigrate

Signed-off-by: tangyang9464 <tangyang9464@163.com>

README.md

@@ -70,7 +70,15 @@ func main() {
 }
 ```
 ## Turn off AutoMigrate
-New an adapter will use ``AutoMigrate`` by default for create table, if you want to turn it off, please use API ``NewAdapterWithoutAutoMigrate(db *gorm.DB) (*Adapter, error)``. Find out more at [gorm-adapter#160](https://github.com/casbin/gorm-adapter/pull/160)
+New an adapter will use ``AutoMigrate`` by default for create table, if you want to turn it off, please use API ``TurnOffAutoMigrate(db *gorm.DB) *gorm.DB``. See example: 
+```go
+db, err := gorm.Open(mysql.Open("root:@tcp(127.0.0.1:3306)/casbin"), &gorm.Config{})
+db = TurnOffAutoMigrate(db)
+// a,_ := NewAdapterByDB(...)
+// a,_ := NewAdapterByDBUseTableName(...)
+a,_ := NewAdapterByDBWithCustomTable(...)
+```
+Find out more details at [gorm-adapter#162](https://github.com/casbin/gorm-adapter/issues/162)
 ## Customize table columns example
 You can change the gorm struct tags, but the table structure must stay the same.
 ```go

adapter.go

@@ -198,12 +198,9 @@ func NewAdapterByDBUseTableName(db *gorm.DB, prefix string, tableName string) (*
 
 	a.db = db.Scopes(a.casbinRuleTable()).Session(&gorm.Session{Context: db.Statement.Context})
 
-	disableMigrate := a.db.Statement.Context.Value(disableMigrateKey)
-	if disableMigrate == nil {
-		err := a.createTable()
-		if err != nil {
-			return nil, err
-		}
+	err := a.createTable()
+	if err != nil {
+		return nil, err
 	}
 
 	return a, nil
@@ -255,15 +252,15 @@ func NewAdapterByDB(db *gorm.DB) (*Adapter, error) {
 	return NewAdapterByDBUseTableName(db, "", defaultTableName)
 }
 
-func NewAdapterWithoutAutoMigrate(db *gorm.DB) (*Adapter, error) {
+func TurnOffAutoMigrate(db *gorm.DB) *gorm.DB {
 	ctx := db.Statement.Context
 	if ctx == nil {
 		ctx = context.Background()
 	}
 
 	ctx = context.WithValue(ctx, disableMigrateKey, false)
 
-	return NewAdapterByDBUseTableName(db.WithContext(ctx), "", defaultTableName)
+	return db.WithContext(ctx)
 }
 
 func NewAdapterByDBWithCustomTable(db *gorm.DB, t interface{}, tableName ...string) (*Adapter, error) {
@@ -383,6 +380,11 @@ func (a *Adapter) casbinRuleTable() func(db *gorm.DB) *gorm.DB {
 }
 
 func (a *Adapter) createTable() error {
+	disableMigrate := a.db.Statement.Context.Value(disableMigrateKey)
+	if disableMigrate != nil {
+		return nil
+	}
+
 	t := a.db.Statement.Context.Value(customTableKey{})
 
 	if t != nil {
@@ -414,6 +416,13 @@ func (a *Adapter) dropTable() error {
 	return a.db.Migrator().DropTable(t)
 }
 
+func (a *Adapter) truncateTable() error {
+	if a.db.Config.Name() == sqlite.DriverName {
+		return a.db.Exec(fmt.Sprintf("delete from %s", a.getFullTableName())).Error
+	}
+	return a.db.Exec(fmt.Sprintf("truncate table %s", a.getFullTableName())).Error
+}
+
 func loadPolicyLine(line CasbinRule, model model.Model) {
 	var p = []string{line.Ptype,
 		line.V0, line.V1, line.V2,
@@ -538,11 +547,7 @@ func (a *Adapter) savePolicyLine(ptype string, rule []string) CasbinRule {
 
 // SavePolicy saves policy to database.
 func (a *Adapter) SavePolicy(model model.Model) error {
-	err := a.dropTable()
-	if err != nil {
-		return err
-	}
-	err = a.createTable()
+	err := a.truncateTable()
 	if err != nil {
 		return err
 	}

adapter_test.go

@@ -194,21 +194,36 @@ func initAdapterWithGormInstanceByName(t *testing.T, db *gorm.DB, name string) *
 
 func initAdapterWithoutAutoMigrate(t *testing.T, db *gorm.DB) *Adapter {
 	var err error
-	hasTable := db.Migrator().HasTable(defaultTableName)
+	var customTableName = "without_auto_migrate_custom_Table"
+	hasTable := db.Migrator().HasTable(customTableName)
 	if hasTable {
-		err = db.Migrator().DropTable(defaultTableName)
+		err = db.Migrator().DropTable(customTableName)
 		if err != nil {
 			panic(err)
 		}
 	}
 
-	a, err := NewAdapterWithoutAutoMigrate(db)
+	db = TurnOffAutoMigrate(db)
+
+	type CustomCasbinRule struct {
+		ID    uint   `gorm:"primaryKey;autoIncrement"`
+		Ptype string `gorm:"size:50"`
+		V0    string `gorm:"size:50"`
+		V1    string `gorm:"size:50"`
+		V2    string `gorm:"size:50"`
+		V3    string `gorm:"size:50"`
+		V4    string `gorm:"size:50"`
+		V5    string `gorm:"size:50"`
+		V6    string `gorm:"size:50"`
+		V7    string `gorm:"size:50"`
+	}
+	a, err := NewAdapterByDBWithCustomTable(db, &CustomCasbinRule{}, customTableName)
 
 	hasTable = a.db.Migrator().HasTable(a.getFullTableName())
 	if hasTable {
 		t.Fatal("AutoMigration has been disabled but tables are still created in NewAdapterWithoutAutoMigrate method")
 	}
-	err = a.db.Migrator().CreateTable(&CasbinRule{})
+	err = a.db.Migrator().CreateTable(&CustomCasbinRule{})
 	if err != nil {
 		panic(err)
 	}