[orm-devel] Re: Postgres & Views

[Diedrich Vorberg]

Hi Mike,

>Ran across something which I wonder if you could consider - the use of "views".

Personally I have never used views. My knowlage of advanced SQL 
features is rather limited I have to admint. But here's a patch for 
you, that you might want to try out.

This will give you a class dbclass.viewclass whoes attributes are read-
only (a set will raise an exception). To access your view you will 
have to create a subclass of that just like you'd create a dbobj for 
a table. The code that goes into adapters.psql.datasource will then 
check if the dbclass passed as an argument is a subclass of dbview 
and not add the relation.oid to the SELECT statement.

You might want to subclass a viewclass from an existing dbclass (the 
relationship table/view looks kinda like class/subclass):

class person(dbclass):
      columns = { this and that }

class view_person(viewclass, person):
      """
      view_person will have the same columns as person.
      It's important to have viewclass as the first class to inherit 
      from or else an SQL exception will be called on a set. (If two 
      methods from baseclasses are named the same the method of the 
      first baseclass will be called).
      """

You might find it a little overdone to introduce another baseclass 
for all those dbclasses you want to use a view with. Perhaps a simple
"is_view" attribute in dbclass would do. This is just a design 
suggestion.

This code is untested, sorry, but I didn't have the time.

Diedrich

PS: If the diff doesn't work download

   http://diedri.ch/orm/orm-0.6-views.tar.gz


diff --recursive orm/orm/adapters/psql/datasource.py mike/orm/adapters/psql/datasource.py
73a74
> import dbclass
159,162c160,165
<         if len(str) == 0:
<             str = dbobj.relation() + ".oid"
<         else:
<             str = "%s.oid, %s" % (dbobj.relation(), str)
---
> 
>         if not issubclass(dbobj, dbclass.viewclass):
>             if len(str) == 0:
>                 str = dbobj.relation() + ".oid"
>             else:
>                 str = "%s.oid, %s" % (dbobj.relation(), str)
diff --recursive orm/orm/dbclass.py mike/orm/dbclass.py
317a318,324
> 
> class viewclass(dbclass):
>     def __init__(self):
>         dbclass.__init__(self)
>     
>     def __setattr__(self, name, value):
>         raise ViewsAreReadOnly("Views are read only!")
diff --recursive orm/orm/errors.py mike/orm/errors.py
53a54
> class ViewsAreReadOnly(Exception): pass



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