Re: Foreign Data Wrapper

Inspecting the multicorn source was helpful.

For the purposes of anyone searching the mailing lists, I needed to access
the quals natively. The code that helped me figure out how to do this was
in the native odbc fdw here:
https://github.com/ZhengYang/odbc_fdw/blob/master/odbc_fdw.c

particularly the odbcBeginForeignScan() and odbcIterateForeignScan(), and
odbcGetQual() functions.

Thanks

On Fri, Nov 13, 2015 at 1:24 PM, Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
wrote:

> On Fri, Nov 13, 2015 at 1:46 PM, Big Mike <newoculus(at)gmail(dot)com> wrote:
>
>> Writing a Foreign Data Wrapper and interested in isolating the WHERE
>> clause to speed up the access of an indexed file on my filesystem. I'm
>> attempting to understand the inner workings of how the data is retrieved so
>> I'm writing code to just handle one case at the moment: WHERE clause on a
>> single column in the foreign 'table'.
>>
>> SELECT * FROM t WHERE testval = 1
>>
>> I have this code so far, an implementation of the IterateForeignScan
>> interface.
>>
>> static TupleTableSlot *
>> bIterateForeignScan(ForeignScanState *node) {
>> ...
>> RestrictInfo *rinfo = (RestrictInfo *)node->ss.ps.qual;
>> ...
>> }
>>
>> yet am not familiar with what I need to do to pick apart RestrictInfo in
>> order to gather 'testvar', '=', and '1' separately so I can interpret and
>> pass those through to my file parser.
>>
>> Am I going about this the correct way or is there another path I should
>> follow?
>>
>
>
> I would look at http://multicorn.org/ which gives you a working python
> framework. You subclass their ForeignDataWrapper class, override the
> __init__() and execute() functions, and that's about it. The execute()
> function has a list called quals that would set you up for the filtering
> you want to do.
>
> I would get the foreign data wrapper fully debugged this way before
> attempting to refactor in C. And when you do finally re-code, you can see
> what multicorn itself did to implement your filters.
>
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