用于检查，插入和返回值的可序列化事务

Question

我正在尝试检查数据库以查看是否存在给定的名称和制造商。如果他们然后返回产品ID。如果它们不是，则将它们插入数据库，创建一个新的productId并返回它。当我打印product_id的值时，此查询返回0。

public int addProduct(String name, String manufacturer) throws SQLException{
    int productId = 0;
    Statement st = null;
    connection.setAutoCommit(false);

    try {
    st = this.connection.createStatement();
    ResultSet rs = st.executeQuery(
    "BEGIN TRAN IF EXISTS (SELECT Products.name, Products.manufacturer FROM Products WITH (updlock, serializable) WHERE (Products.name = name AND Products.manufacturer = manufacturer) BEGIN INSERT INTO Products (product_id, name, category, manufacturer) VALUES (productId, name, null, manufacturer) END IF; COMMIT TRANSACTION;" );

    if(rs.next())
        productId = rs.getInt("product_id");
    else
        System.out.println("Product not added!");

    } catch (SQLException e) {
    System.err.println(e);

    } finally {
        if (st != null) st.close();
    }