refactor: remove unnecessary prepared statement allocation (#6374)

gorm.go

@@ -187,15 +187,9 @@ func Open(dialector Dialector, opts ...Option) (db *DB, err error) {
 		}
 	}
 
-	preparedStmt := &PreparedStmtDB{
-		ConnPool:    db.ConnPool,
-		Stmts:       make(map[string]*Stmt),
-		Mux:         &sync.RWMutex{},
-		PreparedSQL: make([]string, 0, 100),
-	}
-	db.cacheStore.Store(preparedStmtDBKey, preparedStmt)
-
 	if config.PrepareStmt {
+		preparedStmt := NewPreparedStmtDB(db.ConnPool)
+		db.cacheStore.Store(preparedStmtDBKey, preparedStmt)
 		db.ConnPool = preparedStmt
 	}
 
@@ -256,8 +250,15 @@ func (db *DB) Session(config *Session) *DB {
 	}
 
 	if config.PrepareStmt {
+		var preparedStmt *PreparedStmtDB
+
 		if v, ok := db.cacheStore.Load(preparedStmtDBKey); ok {
-			preparedStmt := v.(*PreparedStmtDB)
+			preparedStmt = v.(*PreparedStmtDB)
+		} else {
+			preparedStmt = NewPreparedStmtDB(db.ConnPool)
+			db.cacheStore.Store(preparedStmtDBKey, preparedStmt)
+		}
+
 		switch t := tx.Statement.ConnPool.(type) {
 		case Tx:
 			tx.Statement.ConnPool = &PreparedStmtTX{
@@ -274,7 +275,6 @@ func (db *DB) Session(config *Session) *DB {
 		txConfig.ConnPool = tx.Statement.ConnPool
 		txConfig.PrepareStmt = true
 	}
-	}
 
 	if config.SkipHooks {
 		tx.Statement.SkipHooks = true

prepare_stmt.go

@@ -21,6 +21,15 @@ type PreparedStmtDB struct {
 	ConnPool
 }
 
+func NewPreparedStmtDB(connPool ConnPool) *PreparedStmtDB {
+	return &PreparedStmtDB{
+		ConnPool:    connPool,
+		Stmts:       make(map[string]*Stmt),
+		Mux:         &sync.RWMutex{},
+		PreparedSQL: make([]string, 0, 100),
+	}
+}
+
 func (db *PreparedStmtDB) GetDBConn() (*sql.DB, error) {
 	if dbConnector, ok := db.ConnPool.(GetDBConnector); ok && dbConnector != nil {
 		return dbConnector.GetDBConn()