java - 获取事务中自动增量字段的值

Question

我将 H2DB 用于 litthe cuesheet-database。我正在向具有主键 ID 的 anj 自动增量字段的表中插入几条记录。对于每条记录，我想知道插入后 ID 字段的值，即在提交之前。我如何获得这个值？

Answer 1

简而言之：

• Statement.RETURN_GENERATED_KEYS在准备插入语句时用作第二个参数
• ResultSet插入后从语句中获取.getGeneratedKeys()
• 从中获取生成的 idResultSet

这在使用事务时也应该起作用。

以下示例演示了这一点：

try {
    // register driver
    Class.forName("org.h2.Driver");
    // open connection, in-memory database
    Connection conn = DriverManager.getConnection("jdbc:h2:mem:");
    conn.setAutoCommit(false);
    // create table
    PreparedStatement createSample = conn.prepareStatement("CREATE TABLE sample (id int not null auto_increment, txt varchar(128))");
    createSample.executeUpdate();
    createSample.close();
    // prepare insert statement
    PreparedStatement insertStatement = conn.prepareStatement("INSERT INTO sample (txt) VALUES (?)", Statement.RETURN_GENERATED_KEYS);
    // dummy list with texts
    List<String> dummyTexts = Arrays.asList("Entry A", "Entry B", "Entry C", "Entry D", "Entry E");
    // insert data
    for (String dummyText : dummyTexts) {
        insertStatement.setString(1, dummyText);
        insertStatement.executeUpdate();
        // get generated key
        ResultSet generatedKeys = insertStatement.getGeneratedKeys();
        if ((generatedKeys != null) && (generatedKeys.next())) {
            int generatedKey = generatedKeys.getInt(1);
            System.out.println("generated key " + generatedKey + " for entry '" + dummyText + "'");
        }
    }
    // commit
    conn.commit();
    insertStatement.close();
    // select data
    PreparedStatement selection = conn.prepareStatement("SELECT id, txt FROM sample");
    ResultSet selectionResult = selection.executeQuery();
    while (selectionResult.next()) {
        System.out.println("id: " + selectionResult.getInt(1) + ", txt: '" + selectionResult.getString(2) + "'");
    }
    selectionResult.close();
    selection.close();
    // close connection
    conn.close();
} catch (Exception ex) {
    ex.printStackTrace();
}