PostgreSQL JDBC - isLast() and empty ResultSet

Author

isLast() and empty ResultSet

Ruediger Herrmann

2005-04-21, 8:24 pm

Hello,

I implemented an Iterator interface iterating over a ResultSet. Therefore
I rely on isLast() to implement the Iterator#hasNext() method. This works
fine unless the whole ResultSet is empty.
For empty RresultSets, isLast always returns true.
Stepping through the code I found the reason therefore. Line 544 of
AbstractJdbc2ResultS
et says
if (rows_size == 0)
return false; // No rows.
At least to me this is suspicious as I would return the opposite. Might that
be a bug or is there any other reason to behave like this?

I am using JDBC Driver 8.0 Build 311 and Server Version 8.0.2.

Regards
Rüdiger

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Ruediger Herrmann

2005-04-22, 7:23 am

Thanks a lot to all of you for the replies.

I'm now using isBeforeFirst() to test for an empty
ResultSet, wich as far as my tests show seems to work
if it is the first thing done.

Regards
Rüdiger

--- Oliver Jowett <oliver@opencloud.com> wrote:
> Ruediger Herrmann wrote:
> a ResultSet. Therefore
> Iterator#hasNext() method. This works
> therefore. Line 544 of
> return the opposite. Might that
> like this?
>
> It's not a bug, AFAIK. isLast() returns true if the
> resultset is
> positioned *on* the last row of the resultset. This
> means that if you
> have a 5-row resultset, isLast() is true when the
> 5th row is the
> currently active row (and you can retrieve data from
> that row at that
> point).
>
> For a 0-row resultset, we can never be on the last
> row as there are no
> rows at all.
>
> You could try something like this for your hasNext()
> condition:
>
> rs.isBeforeFirst() || (rs.getRow() != 0 &&
> !rs.isLast())
>
> (note that isBeforeFirst() returns false on an empty
> resultset, per javadoc)
>
> -O
>
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