mr wrote:
Hejhej,
first I'd like to thank the developers of SQLAlchemy for their great
effort. The library works like a treat and is well documented. It's a
pleasure working with it...
Nevertheless I've currently run into a problem when trying to create
classes that are based on read-only reflection from existing database
tables. Here *read-only* means that I have a database table with fixed
contents that I'm not going to change in application. However, I need
this table and its contents to create other objects.
Let's assume we have a table *foos* with a number of rows - each of
them representing a distinct *foo*. There is the usual id column
*foo_id*, then there's *foo_name* and *foo_key*. I've been able to
come up with the following code to that uses reflection to derive the
table metadata.
engine = create_engine('postgresql://...')
Base = declarative_base()
class Foo(Base):
__tablename__ = 'foos
__autoload__ = True
__table_args__ = {'autoload_with': engine}
def __init__(self):
pass
Now when I create a foo object with f = Foo() I can see all columns of
the existing table by doing something like:
print f.metadata.tables[f.__tablename__].columns
What I want to do now is to initialize a *foo*-object by specifying
*foo_key* in the constructor so that I have exactly the one distinct
row containing *foo_key* at my disposal for further processing.
def __init__(self, foo_key):
...
However I was not able to do this... Am I missing something here? Or
did anybody else had a similar problem and was able to solve it...
Thank you very much in advance.
I think you are looking for this
http://www.sqlalchemy.org/trac/wiki/UsageRecipes/UniqueObject
Regards,
Markus
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