On Feb 28, 2011, at 18:21 , Michael Bayer wrote: > Column can be subclassed but because they are intensively used in complex > expression transformations, your custom class may be used in more scenarios > than you first anticipate. > > There are two scenarios where Column objects are copied, and in one case > copied into an altered class, so the "copying" of Column uses an attribute > called _constructor to point to which class should be used when creating this > copy. Usually setting that to Column: > > class MyColumn(Column): > _constructor = Column > > # .... go nuts
LOL!! Thanks > > is all you need. > > > > On Feb 28, 2011, at 10:17 AM, Martijn Moeling wrote: > >> Hi, >> >> I know this is an "OLD" threat but I was searching the group to see If I was >> not the first one doing this. >> >> I am not sure I understand very well what this threat is all about, but I >> want to extend the Column class for a different reason. >> >> I want to add extra functionality to the Column class which is absolutely >> NOT SA related. SA functionality should not be effected though. >> >> say I want to add a config value and some methods for rendering and >> validating screens: >> >> def MyColumn(Column): >> >> def __init(): >> dosomething to init >> >> def ExtraInfo(self): >> do_something_not_sa_related >> >> validation = 'someregex' >> >> >> and use MyColumn in places where I normally use Column(......) >> >> What do I need to take into account, I've done some tests and "Error hell" >> broke loose, where the errors are hidden deep inside SA so hard to overcome. >> >> Martijn >> >> On Dec 11, 2008, at 16:20 , Michael Bayer wrote: >> >>> >>> >>> On Dec 11, 2008, at 3:37 AM, Angri wrote: >>> >>>> >>>> Here it is: http://www.sqlalchemy.org/trac/ticket/1244 >>>> >>>> Maybe it is good idea to drop some new lines in faq? Something like >>>> this: >>>> >>>> Q: How should I extend sqlalchemy.schema.Column? >>>> A: You surely dont need it. Recommended way to achive your possible >>>> needs is to write instance-factory function which decorates creation >>>> of sqlalchemy.schema.Column instances. >>>> >>>> Q: But I'm really need it! >>>> A: Ok. To subclass Column, this is the current recipe: >>>> >>>> from sqlalchemy.sql.util import Annotated, annotated_classes >>>> >>>> class MyColumn(Column): >>>> ... >>>> >>>> class AnnotatedMyColumn(Annotated, MyColumn): >>>> pass >>>> >>>> annotated_classes[MyColumn] = AnnotatedMyColumn >>>> >>>> Do not forget to put AnnotatedMyColumn in the module namespace, or >>>> your schema will not be pickleable! >>>> >>>> Correct me please if I am wrong somewhere and excuse me for my >>>> English. >>> >>> Well the AnnotatedMyColumn part is less than ideal since its an >>> internal. the way that works could very likely change. Creating an >>> AnnotatedXXX class *can* be automated. the pickle thing just might be >>> a caveat we'd document or arrange for an exception to occur (like >>> putting a throw in a __getstate__ method). >>> >>> --~--~---------~--~----~------------~-------~--~----~ >>> You received this message because you are subscribed to the Google Groups >>> "sqlalchemy" group. >>> To post to this group, send email to sqlalchemy@googlegroups.com >>> To unsubscribe from this group, send email to >>> sqlalchemy+unsubscr...@googlegroups.com >>> For more options, visit this group at >>> http://groups.google.com/group/sqlalchemy?hl=en >>> -~----------~----~----~----~------~----~------~--~--- >>> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "sqlalchemy" group. >> To post to this group, send email to sqlalchemy@googlegroups.com. >> To unsubscribe from this group, send email to >> sqlalchemy+unsubscr...@googlegroups.com. >> For more options, visit this group at >> http://groups.google.com/group/sqlalchemy?hl=en. >> > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlalchemy@googlegroups.com. > To unsubscribe from this group, send email to > sqlalchemy+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
