"TYPE_FORWARD_ONLY"错误；在sqlite中 [英] Error with "TYPE_FORWARD_ONLY" in sqlite

问题描述

我正在使用SQLite和JDBC，并收到有关result_set为TYPE_FORWARD_ONLY的错误.

I am working with SQLite and JDBC and getting this error about the result_set being TYPE_FORWARD_ONLY.

    PreparedStatement get_mileage = conn.prepareStatement("SELECT * FROM workout_log");
    ResultSet mileage_count = get_mileage.executeQuery();

    mileage_count.absolute(week_start);

    for (int i=week_start;i<=week_finish;i++){
        total_mileage+=mileage_count.getInt(1);
        mileage_count.next();
    }

即使我不知道它根本没有向后移动，该错误仍在调用absolute()时出现.我尝试将标志添加到prepareStatement，但是它说我的SQLite版本不支持不是FORWARD_ONLY的ResultSet.

The error is on the call to absolute() even though I know it is not moving backwards at all. I have tried adding flags to prepareStatement but it says my version of SQLite does not support ResultSet that is not FORWARD_ONLY.

我的问题是，即使我不向后移动，为什么还会发生这种情况?

My question is why is this occuring, even though I am not moving backward?

推荐答案

TYPE_FORWARD_ONLY ResultSet仅支持next()进行导航，而不支持first()，last()，absolute(int)，relative(int)之类的方法. JDBC规范明确定义了在TYPE_FORWARD_ONLY上调用时抛出SQLException的那些:

A TYPE_FORWARD_ONLY ResultSet only supports next() for navigation, and not methods like first(), last(), absolute(int), relative(int). The JDBC specification explicitly defines those to throw a SQLException if called on a TYPE_FORWARD_ONLY:

:

抛出:
SQLException-如果发生数据库访问错误；在封闭的结果集上调用此方法，或者结果集类型为TYPE_FORWARD_ONLY

Throws:
SQLException - if a database access error occurs; this method is called on a closed result set or the result set type is TYPE_FORWARD_ONLY

对于TYPE_FORWARD_ONLY，使用这些方法没有多大意义:类似于可滚动的结果集，这种类型的结果集不适合行的随机访问".

Using those methods does not make a lot of sense with a TYPE_FORWARD_ONLY: that type of result set is not intended for 'random access' of the rows, like the scrollable result sets are.

例如，使用TYPE_FORWARD_ONLY:

• 仅当您位于第一行之前(并且位于第一行本身)时，调用first()才有效，所以为什么不只使用next()
• 仅当您传递的行比当前行高时调用absolute(int)才有效，并且您再也无法返回到较早的行
• 仅当您传递正值并且永远无法返回到较早的行时，调用relative(int)才有效
• 调用last()将使您跳过结果集的其余部分，并且永远无法返回到较早的行

• Calling first() would only work when you are positioned before the first row (and on the first row itself), so why not just use next()
• Calling absolute(int) would only work if you pass a row higher than the current row, and you could never go back to earlier rows
• Calling relative(int) would only work if you pass a positive value and you can never go back to earlier rows
• Calling last() would make you skip the rest of the result set and you can never go back to earlier rows

诚然:它可能有其用途，但不必要地使驱动程序复杂化为TYPE_FORWARD_ONLY的其他约束.

Admittedly: it might have its uses, but it would needlessly complicate the driver with the additional constraints of being TYPE_FORWARD_ONLY.

如果要随机访问，则需要通过指定滚动性类型TYPE_SCROLL_INSENSITIVE或TYPE_SCROLL_SENSITIVE之一来声明要随机访问.如果您的驱动程序不支持这些类型，则可能需要使用例如CachedRowSet(特别是com.sun.rowset.CachedRowSetImpl)或首先加载整个ResultSet(例如，放入List<? extends List<Object>>)对其进行仿真.

If you want random access, you need to declare that you want random access by specifying one of the scrollability types TYPE_SCROLL_INSENSITIVE or TYPE_SCROLL_SENSITIVE. If your driver doesn't support these types, then you may need to simulate it with for example CachedRowSet (specifically com.sun.rowset.CachedRowSetImpl), or by first loading the entire ResultSet (eg into a List<? extends List<Object>>).

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