java - 无法获取类别 ID ( java/sql )

Question

我有 2 张 table :沙龙库存类别

salon_stock 表有一个类别表的 fk 列 cat_id

类别表有 2 列 cat_id 和标题

在下面的代码中，我尝试插入属于类别名称的cat_id从 JComboBox 检索以及沙龙_股票表的数据

    private void AddStock() throws SQLException,NullPointerException {
int catID = 0; 
String cat=cat_list.getSelectedItem().toString();
            if (cat.equals("Select a Category")) {
                 ResultSet rs = con.createStatement().executeQuery("select * from categories where title=' Default'");

            if(rs.next()){
                catID=rs.getInt("cat_id");
            }
            else{
                throw new SQLException("The 'Default' category was not found in the Categories Table");
            }

            }
            else{
          ResultSet rs = con.createStatement().executeQuery("select * from categories where title=' "+cat+"'");

            if(rs.next()){
               catID=rs.getInt("cat_id");
               }
            }

          ps1 = con.prepareStatement("insert into "+tableName+"(title,price,qty,cat_id) values( ?,?,?,?)");

          ps1.setString(1,title_field.getText());
          ps1.setInt(2,Integer.parseInt(price_field.getText()));
          ps1.setInt(3,Integer.parseInt(qty_field.getText()));
          ps1.setInt(4,catID);
          ps1.executeUpdate();
          ps1.closeOnCompletion();

    }

代码运行良好，但在表中，它将“0”值插入到 stock_table 的 cat_id 列中。

我无法检测到错误..请帮助我..

Answer 1

也许查询中的空格是错误:

"select * from categories where title=' "+cat+"'"

必须是

"select * from categories where title='"+cat+"'"