如何显示条目是否在数据库中？

Question

我目前正在制作一个程序，可以在其中删除数据库中的某些条目。我可以做到这一点，但我想添加一个 JOptionPane 屏幕，以便它何时可以找到它或无法找到它（因此，当未找到名称时，不应找到它并显示一条消息说找不到它）。我尝试使用结果语句，但这似乎不起作用。如果有人知道如何做，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");    }

Answer 1

引用javadoc executeUpdate()：

返回：

(1) SQL 数据操作语言 (DML) 语句的行计数或 (2) 0（不返回任何内容的 SQL 语句）

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);

}