On May 9, 2006, at 7:58 AM, Julien Cigar wrote:
cascade_mappers(Invasive.mapper, InvasiveCategory.mapper) //
Invasive contains invasivecategory and InvasiveCategory contains
invasives
cascade_mappers is pretty sketchy, while its working for you in this
case, i suggest you dont trust it....
It works, but how could I select all "Invasive" order by
InvasiveCategory.category ?
I tried things like:
Invasive.mapper.select_by(order_by=[invasivecategory.category])
Invasive.mapper.select(order_by=[InvasiveCategory.c.category]) //
This query doesn't fail, but a JOIN is missing ... (why ?)
...
First of all, select_by(), which I am cursing ever having added, does
not do "order_by". the "order_by" youre putting in there, as far as
it can tell, means "look for a property named 'order_by' on the
"Invasive" class", which of course there isnt. all keyword arguments
must relate to properties on the Invasive class, therefore theres no
order_by, no limit, no offset, etc. all of that stuff is available
when you use select().
then when using select(), it requires total explicitness. when you
deal with the Invasive mapper, its as though you are sitting at a SQL
prompt and querying the "invasive" table, except youre going to get
back Invasive objects, not rows. So if you want to select from
invasive and order by a relationship to another table, i.e.
invasive_category, you have to join:
Invasive.mapper.select
(invasives.c.category==invasive_categories.c.id,
order_by=invasivecategory.c.category)
Another question, why can't I select only some fields in a
select_text() ? For example :
Invasive.mapper.select_text('SELECT a.* FROM invasives a,
invasive_categories b WHERE a.category=b.id') works
but Invasive.mapper.select_text('SELECT a.original_name FROM
invasives a, invasive_categories b WHERE a.category=b.id') fails ...
select_text is not a terrific method since its hard to use; it
requires that the columns in the result set match exactly what the
mapper would normally create on its own. so you cant just select
"a.original_name", since the mapper cannot create an "Invasive"
object from just a name; you have to select all the columns from the
"invasives" table.
if you were doing eager loads, it would be even more difficult
(acutally impossible, since it generates aliased column names for
related objects). in 0.2, the eager loads will just silently degrade
to lazy loads if the proper columns are not present.
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