I don't really think it's a bug. Calling Thing.all.last does a query for the last item in the db, because Thing#all returns a DM Query, and the #last updates that query.
Here are ways using mysql: http://www.mysqltutorial.org/select-nth-highest-record-database-table-using-mysql.aspx As you can see, they all rely on sub queries, some of which I don't think can be done in DM without writing sql. Here are other approaches: Thing.all(:limit =>10).to_a.last <- will find 10 records and return the last of the array Thing.all(:limit => 10) - Thing.all(:limit => 9) <- executes a single query returning an array of the 1 item. I really think the offset approach you already figured out is the best though. On Jan 13, 9:45 pm, Robert Fletcher <[email protected]> wrote: > Well, I discovered this workaround: > > a = Task.all(:order => [ :ordering.asc ])[9] > > Looks like this optimizes to what the previous one probably ought to. It > uses OFFSET. > > > > On Thu, Jan 13, 2011 at 7:33 PM, lobati <[email protected]> wrote: > > So I'm trying to get the nth result from the database: > > > a = Task.all(:limit => 10, :order => [ :ordering.asc ]).last > > > but this query, instead of returning the 10th item actually returns > > the last item in the database. I get the same results if I do this: > > > a = Task.all(:limit => 10, :order => [ :ordering.asc ]) > > a = a.last > > > However, I get the results I want if I do something like this: > > > a = Task.all(:limit => 10, :order => [ :ordering.asc ]) > > a.each do |task| > > # do nothing > > end > > a = a.last > > > I gather this is the result of some query optimization going on, but > > this is a bug, right? So for the time being, is there are better way > > of forcing the query to take place before '.last' and/or is there a > > more efficient way for me to get the 10th record with the above > > condition? > > > -- > > You received this message because you are subscribed to the Google Groups > > "DataMapper" group. > > To post to this group, send email to [email protected]. > > To unsubscribe from this group, send email to > > [email protected]<datamapper%2Bunsubscribe@googlegrou > > ps.com> > > . > > For more options, visit this group at > >http://groups.google.com/group/datamapper?hl=en. -- You received this message because you are subscribed to the Google Groups "DataMapper" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/datamapper?hl=en.
