如何显示条目是否在数据库中？答案

【问题标题】：How to show if a entry is in a database?如何显示条目是否在数据库中？
【发布时间】：2019-11-03 04:48:42
【问题描述】：

我目前正在制作一个程序，我可以在其中删除数据库中的某些条目。我可以做到，但我想添加一个 JOptionPane 屏幕，用于显示何时可以或找不到它（因此，当找不到名称时，不应该找到它并显示一条消息说它找不到）。我尝试使用结果语句，但这似乎不起作用。如果有人知道怎么做，请评论如何做！

private void btnDeleteActionPerformed(java.awt.event.ActionEvent evt) {                                          
    ArrayList<Cookbook  > recipes = new ArrayList();
    String name = txtName.getText();
    try {
        String url = "jdbc:derby://localhost:1527/Cookbook";
        Connection conn = DriverManager.getConnection(url);
        String query = "DELETE from RECIPES WHERE NAME = ?";
        PreparedStatement pst = conn.prepareStatement(query);
        pst.setString(1, name);
        pst.executeUpdate();




        JOptionPane.showMessageDialog(null, name + " was sucessfully deleted");
    } catch (Exception e) {
        JOptionPane.showMessageDialog(null, "was not found or could not be deleted");
    }

【问题讨论】：

标签： java sql database joptionpane

【解决方案1】：

引用executeUpdate()的javadoc：

返回：

对于 SQL 数据操作语言 (DML) 语句，可以是 (1) 行数，对于不返回任何内容的 SQL 语句，可以是 (2) 0

所以：

String url = "jdbc:derby://localhost:1527/Cookbook";
try (Connection conn = DriverManager.getConnection(url)) {
    String query = "DELETE from RECIPES WHERE NAME = ?";
    try (PreparedStatement pst = conn.prepareStatement(query)) {
        pst.setString(1, name);
        int rowCount = pst.executeUpdate();
        if (rowCount == 0) {
            JOptionPane.showMessageDialog(null, "'" + name + "' was not found");
        } else if (rowCount == 1) {
            JOptionPane.showMessageDialog(null, "'" + name + "' was successfully deleted");
        } else { // cannot happen if `NAME` has unique index in the database
            JOptionPane.showMessageDialog(null, rowCount + " recipes named '" + name + "' were deleted");
        }
    }
} catch (Exception e) {
    JOptionPane.showMessageDialog(null, "something went wrong: " + e);
}

【讨论】：