Mike, I remember an article of yours where you described much of the
process of creating a new dialect for SA, for a Java database if I'm not
mistaken. I wasn't able to find it, though.
:)
On 04/08/2015 01:19 AM, Mike Bayer wrote:
On 4/7/15 1:59 PM, Ralph Heinkel wrote:
Hello dialect experts,
what would be the best approach for creating a SqlAlchemy dialect for
a new database system?
Are there any recipes available for this area, or is the way to go to
read code of existing dialects and derive my own dialect from those?
I had a first glance at some built-in dialects, and also some in
external packages ... it is not always obvious to me why certain
classes and methods have been implemented.
The obvious thing is to create a subclass of
sqlalchemy.enginedefault.DefaultDialect, but how would I know which
methods and class attributes to override/implement, except for going
through the trial and error approach?
And then there are other classes which are implemented in some
dialects, like compiler.DDLCompiler, compiler.GenericTypeCompiler,
and so on ... where and how would I start best?
Any help would be very much appreciated.
Start with the README for new dialects:
https://bitbucket.org/zzzeek/sqlalchemy/src/44a9820b4e02f65b3884fa2c016efce9663e4910/README.dialects.rst?at=master
that will show the guidelines for writing new dialects.
Then to see some examples of that layout, take a look at some of the
3rd party dialects listed at:
http://docs.sqlalchemy.org/en/latest/dialects/index.html#production-ready
Also the "sqlalchemy-access" dialect is basically something of a
"demo" for the layout, which I basically put there after extracting it
from SQLAlchemy main where it had been for many years. It might not
be 100% up to date, but mostly follows that guideline and even passed
tests at one point, that's at
https://bitbucket.org/zzzeek/sqlalchemy-access.
The key thing you'll be doing is running the suite tests, which will
be part of the test suite within your own dialect. So yes, you start
with a fairly plain subclass of DefaultDialect, then you probably want
to get a "hello world" kind of program going where you just see if
"create_engine" and then "engine.execute("select * from table")" work
at all, and then the suite tests should test a lot more.
Ciao ciao
Ralph
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