Use explicit transactions (#11)

* Use explicit transactions for DB manipulations

* Preallocate memory for strings.Builder

* Use tx.Close instead of tx.Rollback

adapter.go

@@ -133,6 +133,12 @@ func (r *CasbinRule) String() string {
 	const prefixLine = ", "
 	var sb strings.Builder
 
+	sb.Grow(
+		len(r.PType) +
+			len(r.V0) + len(r.V1) + len(r.V2) +
+			len(r.V3) + len(r.V4) + len(r.V5),
+	)
+
 	sb.WriteString(r.PType)
 	if len(r.V0) > 0 {
 		sb.WriteString(prefixLine)
@@ -215,7 +221,13 @@ func savePolicyLine(ptype string, rule []string) *CasbinRule {
 
 // SavePolicy saves policy to database.
 func (a *Adapter) SavePolicy(model model.Model) error {
-	_, err := a.db.Model((*CasbinRule)(nil)).Where("id IS NOT NULL").Delete()
+	tx, err := a.db.Begin()
+	if err != nil {
+		return fmt.Errorf("start DB transaction: %v", err)
+	}
+	defer tx.Close()
+
+	_, err = tx.Model((*CasbinRule)(nil)).Where("id IS NOT NULL").Delete()
 	if err != nil {
 		return err
 	}
@@ -237,20 +249,33 @@ func (a *Adapter) SavePolicy(model model.Model) error {
 	}
 
 	if len(lines) > 0 {
-		_, err = a.db.Model(&lines).
+		_, err = tx.Model(&lines).
 			OnConflict("DO NOTHING").
 			Insert()
+		if err != nil {
 			return err
 		}
+	}
+
+	err = tx.Commit()
+	if err != nil {
+		return fmt.Errorf("commit DB transaction: %v", err)
+	}
+
 	return nil
 }
 
 // AddPolicy adds a policy rule to the storage.
 func (a *Adapter) AddPolicy(sec string, ptype string, rule []string) error {
 	line := savePolicyLine(ptype, rule)
+	err := a.db.RunInTransaction(func(tx *pg.Tx) error {
 		_, err := a.db.Model(line).
 			OnConflict("DO NOTHING").
 			Insert()
+
+		return err
+	})
+
 	return err
 }
 
@@ -275,7 +300,10 @@ func (a *Adapter) AddPolicies(sec string, ptype string, rules [][]string) error
 // RemovePolicy removes a policy rule from the storage.
 func (a *Adapter) RemovePolicy(sec string, ptype string, rule []string) error {
 	line := savePolicyLine(ptype, rule)
-	err := a.db.Delete(line)
+	err := a.db.RunInTransaction(func(tx *pg.Tx) error {
+		return a.db.Delete(line)
+	})
+
 	return err
 }
 
@@ -320,7 +348,11 @@ func (a *Adapter) RemoveFilteredPolicy(sec string, ptype string, fieldIndex int,
 		query = query.Where("v5 = ?", fieldValues[5-fieldIndex])
 	}
 
+	err := a.db.RunInTransaction(func(tx *pg.Tx) error {
 		_, err := query.Delete()
+		return err
+	})
+
 	return err
 }