you can overrride create_instance() in a MapperExtension object.
FYI, in 0.2 the __init__ method is not even called when objects are
loaded from the DB (but you can still use create_instance() to apply
specific behavior).
On May 10, 2006, at 2:50 PM, Marty McFly wrote:
I just discovered that the approach I had planned for my __init__-
constructor does not work. When SA calls the __init__ method of my
class, it does not pass any parameters and the attributes defined
for this class/object do not exist yet.
Is there a way to access attributes in the __init__ -method? (I
mean, when SA reads the rows from the DB and creates the objects).
I would like to do something as follows:
def __init__(self, ownerId = None, prepForView = True):
if prepForView:
self.editable = (self.ownerId == session['userId'])
But I do not know how to do this, since ownerId is a mapped
attribute and is not available in the __init__-call.
Thanks, Martin
Actually, it might get a little bit more complicated than that,
because I
would like to allow the users to choose who can comment on their
posts, for
example: all people, only logged in people, only friends, ...
So, for the posts the overhead probably gets big because it
depends on the
identity of the viewer, on the blog and on the user-settings for
this blog.
That's why I only want to do these checks when the blog entries and
comments are passed to the view.
You suggest to check for the existence of the primary key ('id' in my
case), because all the new objects that I create do not yet have a
primary
key since it will be assigned from the database later? Right? Hmm,
that
would solve most of my problems. But when somebody edits a post
and then
commits the changes, then it is unnecessary to prepare the
permission-attributes for the view, but the primary key exists
already.
In the meantime, I came up with a slightly different solution.
Don't know
if it is good, but maybe it helps other people in similar
situations to
read this. I extended the constructor call with a parameter
"prepForView"
like this:
__init__(self, firstAttribute, secondAttribute, ..., prepForView =
True):
so I can check at the end of the constructor:
if prepForView:
do all the permission assignments
So, when I get an object from the DB, prepForView has its
default=True, and
when I create a new object, I can create it with:
newPost = model.Post(prepForView = False)
and thus avoid the overhead of the permission assignments.
Totally different question:
I have a class Post that inherits from a more general class Item.
In my
assignment of the Item.mapper, I overrode some of the column
names, with
the properties = {
'contextId' : item.c.context_id
..
}
But I just discovered (after 3 hours of looking for the problem),
that when
I assign a mapper to the Post-class and inherit from the
Item.mapper, I
have to override all the column names again! When I didn't
override them in
Post.mapper at first, the inheritance-mapper used "context_id" as
attribute
name instead of "contextId". Did I miss some kind of flag like
"useParentProperties" so I don't have to repeat all assignments (code
duplication)?
Anyway, thanks Gambit for your input!
Cheers, Martin
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