如果Java生产代码中不存在并在JUnit中确认,则创建数据库表

Question

我正在用Java编写数据库程序,并且想要创建一个表(如果它还不存在).我从中了解DatabaseMetaData.getTables()了如何在Java中检测SQL表的存在？而我正在尝试使用它:

private boolean tableExists() throws SQLException {
    System.out.println("tableExists()");

    DatabaseMetaData dbmd = conn.getMetaData();
    ResultSet rs = dbmd.getTables(null, null, this.getTableName(), null);

    System.out.println("TABLE_NAME: " + rs.getString("TABLE_NAME"));

    return rs.getRow() == 1;
}

问题是即使在创建表之后rs.getRow()总是返回0.使用rs.getString("TABLE_NAME")抛出异常表明结果集为空.

我想到的一个可能的解决方案是执行CREATE TABLE语句并捕获抛出的任何异常.但是,我不喜欢在程序的控制流程中使用异常的想法.

FWIW,我正在使用HSQLDB.但是,我想编写独立于RDMS引擎的Java代码.有没有其他方法可以DatabaseMetaData.getTables()用来做我想要的事情？或者是否有其他解决方案来编写我的tableExists()方法？

添加:

使用这里给出的建议,我找到了一个似乎适用于我的生产代码的解决方案:

private void createTable() throws SQLException {
    String sqlCreate = "CREATE TABLE IF NOT EXISTS " + this.getTableName()
            + "  (brand           VARCHAR(10),"
            + "   year            INTEGER,"
            + "   number          INTEGER,"
            + "   value           INTEGER,"
            + "   card_count           INTEGER,"
            + "   player_name     VARCHAR(50),"
            + "   player_position VARCHAR(20))";

    Statement stmt = conn.createStatement();
    stmt.execute(sqlCreate);
}

现在我也在编写一个JUnit测试来断言表确实已经创建了:

public void testConstructor() throws Exception {
    try (BaseballCardJDBCIO bcdb = new BaseballCardJDBCIO(this.url)) {
        String query = "SELECT count(*) FROM information_schema.system_tables WHERE table_name = '" + bcdb.getTableName() + "'";
        Connection conn = DriverManager.getConnection(this.url);
        Statement stmt = conn.createStatement();
        ResultSet rs = stmt.executeQuery(query);
        Assert.assertTrue(rs.next());
        Assert.assertEquals(1, rs.getInt(1));
        Assert.assertFalse(rs.next());
    }
}

此测试assertEquals()在以下消息上失败:

FAILED: expected: <1> but was: <0>

Answer 1

我发现的解决方案似乎有效:

private void createTable() throws SQLException {
    String sqlCreate = "CREATE TABLE IF NOT EXISTS " + this.getTableName()
            + "  (brand           VARCHAR(10),"
            + "   year            INTEGER,"
            + "   number          INTEGER,"
            + "   value           INTEGER,"
            + "   card_count           INTEGER,"
            + "   player_name     VARCHAR(50),"
            + "   player_position VARCHAR(20))";

    Statement stmt = conn.createStatement();
    stmt.execute(sqlCreate);
}

我不得不把它放在IF NOT EXISTS我的SQL语句中的正确位置.