Hi Folks,
I have been scratching my head over this one all day, so any advice
would be greatly appreciated!
I have a pretty simple join table setup like this:
foo foo_bar bar
-------------------------------------------
id id_foo (unique) id
id_bar
more_stuff
It looks like a many-to-many relationship, but it's not, since id_foo
is unique in the join table.
- There can be any number of 'foo' for each 'bar'
- Each 'foo' has exactly one or zero 'bar'
I have set up the required declarative stuff, and an association proxy
in 'foo' to get to 'bar' in one nice step. Since there can only ever
be one (or zero - and this is my problem) I have set it to be a
scalar.
It all works great, except that if I try and look at the value of the
assoication proxy in a 'foo' row without a corresponding 'foo_bar',
then I get AttributeError. It is clearly looking for a 'bar' in a
'foo_bar' that is a None (since there is no entry), so is
understandable; but in my case not desirable.
What I would like to do is to get a 'bar' if one exists, else return a
'None'. Is the only way to do this to write my own wrapper property
that does a try/catch? And if I do this, will the property stop being
nice and magical (you know, filterable and comparable etc..)
I am quite a newcomer to SQLAlchemy so go easy on me!
All the best,
Philip
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