[web2py] Re: dal aggregation sum fields None
lines[cash_price]=lines(cash_price) or 0 On Oct 22, 7:50 am, Anthony abasta...@gmail.com wrote: On Saturday, October 22, 2011 7:47:08 AM UTC-4, apple wrote: I am summing some data using the DAL: cash_price = db.orderline.cash_price.sum() lines = db(db.orderline.order_ == id).select(cash_price).first() However if there are no lines then lines[cash_price] is None. So I added: lines[cash_price]=lines[cash_price] or 0 But this does not work either. You have to do: lines[cash_price]=lines._extra[cash_price] or 0 This is OK as it works. But wouldn't it be better if the sum were 0 in the first place? Or if there is some logical reason for it to None then one should to be able to say: lines[cash_price]=lines[cash_price] or 0 I don't think you necessarily want it to default to 0 whenever no records are found, as you might want to distinguish between that case (None) and when there are records but the sum is truly 0. However, it would be nice if the assignment above worked without needing to refer to _extra. Anthony
[web2py] Re: dal aggregation sum fields None
On Sunday, October 23, 2011 11:49:31 AM UTC-4, Massimo Di Pierro wrote: lines[cash_price]=lines(cash_price) or 0 I don't think that will solve the problem. That will add a new 'SUM(orderline.cash_price)' key to lines rather than updating lines._extra['SUM(orderline.cash_price)']. However, when you subsequently do lines[cash_price], it will pull the old value from lines._extra['SUM(orderline.cash_price)'] and ignore the new value stored in the new key. This is because Row.__getitem__ always gets the value stored in _extra when the key is in _extra ( http://code.google.com/p/web2py/source/browse/gluon/dal.py#3888). To enable the assignment, I guess you'd have to update Row.__setitem__ so it would update _extra when the key is in _extra (though not sure if there are any downsides to that). Anthony
[web2py] Re: dal aggregation sum fields None
You are right. I misunderstood the issue. On Oct 23, 11:21 am, Anthony abasta...@gmail.com wrote: On Sunday, October 23, 2011 11:49:31 AM UTC-4, Massimo Di Pierro wrote: lines[cash_price]=lines(cash_price) or 0 I don't think that will solve the problem. That will add a new 'SUM(orderline.cash_price)' key to lines rather than updating lines._extra['SUM(orderline.cash_price)']. However, when you subsequently do lines[cash_price], it will pull the old value from lines._extra['SUM(orderline.cash_price)'] and ignore the new value stored in the new key. This is because Row.__getitem__ always gets the value stored in _extra when the key is in _extra (http://code.google.com/p/web2py/source/browse/gluon/dal.py#3888). To enable the assignment, I guess you'd have to update Row.__setitem__ so it would update _extra when the key is in _extra (though not sure if there are any downsides to that). Anthony
[web2py] Re: dal aggregation sum fields None
On Sunday, October 23, 2011 3:16:56 PM UTC-4, Massimo Di Pierro wrote: You are right. I misunderstood the issue. Do you think assignments to _extra should be enabled (transparently, not by directly hacking the _extra dictionary), or should _extra remain read-only? The current behavior is a bit mysterious -- you can seemingly make an assignment to links[cash_price] without receiving an error, but when you try to retrieve the new value, it's not there. Anthony
[web2py] Re: dal aggregation sum fields None
I am not happy with extra. Currently we have three mechanisms to deal with extra fields. table._extra, lazy virtual fields, links in grid/smartgrid. None of them are undocumented in the book which means that for none of them we promise backward compatibility. Massimo On Oct 23, 2:27 pm, Anthony abasta...@gmail.com wrote: On Sunday, October 23, 2011 3:16:56 PM UTC-4, Massimo Di Pierro wrote: You are right. I misunderstood the issue. Do you think assignments to _extra should be enabled (transparently, not by directly hacking the _extra dictionary), or should _extra remain read-only? The current behavior is a bit mysterious -- you can seemingly make an assignment to links[cash_price] without receiving an error, but when you try to retrieve the new value, it's not there. Anthony
[web2py] Re: dal aggregation sum fields None
On Sunday, October 23, 2011 5:14:17 PM UTC-4, Massimo Di Pierro wrote: I am not happy with extra. Currently we have three mechanisms to deal with extra fields. table._extra, lazy virtual fields, links in grid/smartgrid. None of them are undocumented in the book which means that for none of them we promise backward compatibility. Right now, Row._extra is used to store the results of expressions (such as aggregate functions) in selects. The key used to store the expression is the expression itself, and I think that does have to remain backward compatible (i.e., row[expression] should retrieve the value of the expression returned by the select, regardless of the internal implementation). The question is whether it should be possible to do row[expression] = some_other_value (i.e., alter the value returned by the select). Currently it is not possible without hacking _extra. We could make it possible now, which would involve making an assignment to _extra in Row.__setitem__, and if the internal implementation of _extra fields in Row objects changes in the future, presumably we could just make sure the new implementation also allows such assignments. In other words, should the API allow assignments to expression results in Row objects (without reference to _extra), or should they remain read-only? Anthony
[web2py] Re: dal aggregation sum fields None
On Saturday, October 22, 2011 7:47:08 AM UTC-4, apple wrote: I am summing some data using the DAL: cash_price = db.orderline.cash_price.sum() lines = db(db.orderline.order_ == id).select(cash_price).first() However if there are no lines then lines[cash_price] is None. So I added: lines[cash_price]=lines[cash_price] or 0 But this does not work either. You have to do: lines[cash_price]=lines._extra[cash_price] or 0 This is OK as it works. But wouldn't it be better if the sum were 0 in the first place? Or if there is some logical reason for it to None then one should to be able to say: lines[cash_price]=lines[cash_price] or 0 I don't think you necessarily want it to default to 0 whenever no records are found, as you might want to distinguish between that case (None) and when there are records but the sum is truly 0. However, it would be nice if the assignment above worked without needing to refer to _extra. Anthony
