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Re: isLast() and empty ResultSet

From: Oliver Jowett <oliver(at)opencloud(dot)com>
To: Ruediger Herrmann <ruediger(dot)herrmann(at)gmx(dot)de>
Cc: pgsql-jdbc(at)postgresql(dot)org
Subject: Re: isLast() and empty ResultSet
Date: 2005-04-21 22:16:37
Message-ID: 42682645.4030104@opencloud.com (view raw or flat)
Thread:
Lists: pgsql-jdbc
Ruediger Herrmann wrote:
> 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
> AbstractJdbc2ResultSet 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?

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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