mapping objects

Rita rmorgan466 at gmail.com
Sun Feb 2 13:41:59 CET 2014


Thanks for the response Cameron. No amount of 'googling' could provide me
with that caliber response :-)

So, it seems regardless I would need a database.





On Sun, Feb 2, 2014 at 1:58 AM, Cameron Simpson <cs at zip.com.au> wrote:

> On 01Feb2014 20:46, Rita <rmorgan466 at gmail.com> wrote:
> > I want to learn more about ORMs so I stumbled upon, SqlAlchemy.
> >
> > If i had a JSON document (or XML, CSV, etc.._) is it possible to convert
> it
> > to a SQLAlchemy objects? I like the ability to query/filter (
> >
> http://docs.sqlalchemy.org/en/rel_0_9/orm/tutorial.html#common-filter-operators
> )
> >  the
> > data assuming I set up the proper schema.
>
> Well, not as directly as you might hope. As I recall, SQLAlchemy
> ORMs provide an easy way to make objects representing database
> entities and whose methods automatically drive the necessary SQL
> actions to manipulate them.
>
> On that basis, you won't get anywhere without loading up the
> JSON/XML/etc, parsing it for relevant information (trivial with
> CSV, less so for structured data like JSON or XML), and storing it
> in a database. To which you then point SQLAlchemy.
>
> So you're already doing the fiddly bit just to get stuff into the database.
>
> The neat filter operations you cite are actually done by special
> methods on the objects representing tables and columns. For example,
>
>   User.name == None
>
> is done via the __eq__ method of "User.name". And they return
> strings: bare SQL. The beauty of this is that one can write almost
> idiomatic python, and SQLA will generate correct SQL in the right
> dialect for the database backend, and with all the values correctly
> escaped.
>
> However, it does presume you _already_ have a backend that can be
> queried with SQL.
>
> > Also, is this a valid way to use an ORM suite?
>
> Well, in principle sure. But SQLA won't do it for you directly. It really
> is for data already stored in an SQL queriable database.
>
> Your point about using SQLA's filter operations is right, _provided_
> you have already loaded the original data into a database with the
> right schema. If you've done that work, then SQLA may well serve
> you well from that point on.
>
> Cheers,
> --
> Cameron Simpson <cs at zip.com.au>
>
> We knew Army cadets were involved because they cut through two fences
> to get to the goats, and 15 feet away there was an unlocked gate.
>         - a director of sports information in the Navy, regarding the theft
>           of some mascots from the Naval Academy by Army rivals
> --
> https://mail.python.org/mailman/listinfo/python-list
>



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