On 30 January 2016 at 08:22, Frank Millman <fr...@chagford.com> wrote:
> There are times when I want to execute a SELECT statement, and test for
> three possibilities -
> - if no rows are returned, the object does not exist
> - if one row is returned, the object does exist
> - if more that one row is returned, raise an exception
>
> We had a recent discussion about the best way to do this, and ChrisA
> suggested the following, which I liked -
>
> cur.execute('SELECT ...)
> try:
> row = next(cur)
> except StopIteration:
> # row does not exist
> else:
> try:
> next_row = next(cur)
> except StopIteration:
> # row does exist
> else:
> # raise exception
The simplest thing would just be to call list(cur) but I realise that
you don't want to consume more than 2 rows from the database so just
use islice:
rows = list(islice(cur, 2)) # pull at most 2 rows
if not rows:
# no rows
elif len(rows) > 1:
# too many rows
row = rows[0]
Depending on your application if you just want to raise any error when
there's not exactly one row then you could just do:
(row,) = list(islice(cur, 2))
--
Oscar
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