On Jan 21, 2011, at 1:36 PM, Michael Bayer wrote:
>
> On Jan 21, 2011, at 12:56 PM, A.M. wrote:
>
>> Hello,
>>
>> I would like SQLAlchemy to generate views much in the same way it can
>> generate tables- perhaps like this:
>>
>> View('bob',select([...]))
>>
>> Is the SQLAlchemy code modular enough to support a user-defined SchemaItem
>> or does that require changes to SQLAlchemy itself?
>>
>> The reason I would very much like this is because I currently use the Table
>> objects, munge them through a processor to add common attributes, and
>> generate a schema- I would like to be able to do the same with View objects.
>>
>> I looked at subclassing sqlalchemy.schema.Table, but the __new__ override
>> and the fact that the sql.compiler.DDLCompiler has hardcoded
>> visit_create_<schemaitem> names gives me pause as to whether or not this can
>> be accomplished without modifying SQLAlchemy itself.
>>
>> I realize that questions surrounding view pop up from time-to-time, so does
>> it make sense to create or support a dialect-specific or user-defined
>> SchemaItem?
>>
>> Thanks!
>
> You may not be aware that we have a full API for creation of custom SQL
> expression subclasses as well as establishing compilation rules, which is
> documented at http://www.sqlalchemy.org/docs/core/compiler.html .
>
> Regarding views specifically, we've got a usage recipe against this system,
> though I don't know if its seen any real world usage, at
> http://www.sqlalchemy.org/trac/wiki/UsageRecipes/Views . Its using
> lower-case table() objects as the core structure, which is your basic "thing
> with a bunch of columns" object, the superclass of Table that doesn't have
> the hard linkages with MetaData or constraints, so no SchemaItem subclass is
> needed. Subclassing TableClause (the result of table()) would be the likely
> way to go if you wanted your view construct to have extra features.
>
I guess I am curious as to why there should be a "built-in" way to compile
SchemaItems and then a "user" way to do the same thing. Is there a plan to
unify these methods?
As a python programmer, it seems more natural to me to subclass the relevant
class than to spam my class with decorators. Does it make sense to offer
user-defined SchemaItems which would play well with metadata much like there
are user-defined types?
Cheers,
M
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