ResultSet.TYPE_SCROLL_SENSITIVE的行为 [英] Behaviour of ResultSet.TYPE_SCROLL_SENSITIVE

问题描述

我对类型为TYPE_SCROLL_SENSITIVE的ResultSet的行为感到困惑.

I am confused about the behaviour of a ResultSet that is of type TYPE_SCROLL_SENSITIVE.

我对此的理解是:

1. 我执行一个选择查询，该查询返回一个结果集.我在第一行中打印出特定列的值.
2. 然后我执行Thread.sleep(10000)，这将使程序暂停10秒钟.
3. 程序处于休眠状态时，我手动更新了数据库中的同一列(通过SQL提示符).
4. 10秒后，我再次在结果集的第一行中打印同一列的值.

1. I execute a select query that returns me a result set. I print out the value of a particular column in the first row.
2. I then execute Thread.sleep(10000), which halts the program for 10 seconds.
3. While the program is sleeping, I manually do an update to the same column in the DB (through the SQL prompt).
4. After 10 seconds, I again print the value of the same column in the first row of the result set.

在第4步中，我希望打印的列值与在第1步中打印的值不同.但是，我总是得到相同的值(即使我的ResultSet的类型为SCROLL_TYPE_SENSITIVE).

In step 4, I expect the printed column value to be different from the value printed in step 1. But I always get the same value (even if my ResultSet is of type SCROLL_TYPE_SENSITIVE).

我在这里误会了什么吗?

Am I misunderstanding something here ?

下面是我使用的代码.

private void doStuff() throws Exception
{
    final String query = "select * from suppliers where sup_id=420";

    Statement stmt = this.con.createStatement(
        ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);

    ResultSet rs = stmt.executeQuery(query);

    rs.next();

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

    Thread.sleep(10000); // While this executes, I do a manual update !

    System.out.println("City : " + rs.getString("city"));
}

推荐答案

我在这里误会了吗?

Am I mis-understanding something here ?

是的.您必须重新获取以获取表的最新状态，方法是自己启动SELECT或调用ResultSet.refreshRow().此外，请阅读 ，然后再使用它，否则可能会得到意想不到的结果.

Yes. You must fetch again to get the latest state of the table, either by firing up a SELECT yourself, or calling ResultSet.refreshRow(). Moreover, read the docs of ResultSet.refreshRow() before using it, otherwise you might get unexpected results.

文档中有关TYPE_SCROLL_SENSITIVE的信息，

The doc states regarding TYPE_SCROLL_SENSITIVE,

TYPE_SCROLL_SENSITIVE

TYPE_SCROLL_SENSITIVE

指示类型的常量 可滚动的ResultSet对象 并且通常对变化敏感 别人造的.

The constant indicating the type for a ResultSet object that is scrollable and generally sensitive to changes made by others.

这仅表示它将对同一ResultSet对象中其他人所做的更改敏感.为了理解这个概念，我建议您看一下这个官方的 JDBC教程:更新表.

Which merely means that it would be sensitive to the changes made by others in the same ResultSet object. To understand the concept, I would advise to look at this official JDBC Tutorial: Updating Tables.

好的，编辑我的帖子，使其包含原始教程中的特定行，

Okay, editing my post to include the specific line from the original tutorial,

通过可滚动的结果集，您可以 移至您要更改的行，并 如果类型是TYPE_SCROLL_SENSITIVE， 您可以连续获取新值 更改后.

With a scrollable result set, you can move to rows you want to change, and if the type is TYPE_SCROLL_SENSITIVE, you can get the new value in a row after you have changed it.

这篇关于ResultSet.TYPE_SCROLL_SENSITIVE的行为的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！