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From Sutou Kouhei <...@clear-code.com>
Subject Re: [C-Glib] - writing an extension array
Date Fri, 27 Nov 2020 06:36:33 GMT
Hi,

Thanks.

We need to implement garrow_field_get_meatadata(),
garrow_field_with_metadata() and
garrow_field_with_merged_metadata(). I'll do it before
Apache Arrow 3.0.0.

So you can't read extension type for now. Sorry.


Thanks,
--
kou

In 
 <CS1PR8401MB0822A99D196DD438B14D6D22EBF80@CS1PR8401MB0822.NAMPRD84.PROD.OUTLOOK.COM>
  "Re: [C-Glib] - writing an extension array" on Fri, 27 Nov 2020 05:15:56 +0000,
  Ishan Anand <anand.ishan@outlook.com> wrote:

> Hi Kou
> 
> Sure. Here are the code snippets as a github gist - https://gist.github.com/ananis25/0b645ef94a70a0834fd23177e8721be9
> 
> Thank you for looking.
> 
> 
> ________________________________
> From: Sutou Kouhei <kou@clear-code.com>
> Sent: Friday, November 27, 2020 8:41 AM
> To: user@arrow.apache.org <user@arrow.apache.org>
> Subject: Re: [C-Glib] - writing an extension array
> 
> Hi,
> 
> Could you provide the Python script you used and the C
> program you used?
> 
> 
> Thanks,
> --
> kou
> 
> In
>  <CS1PR8401MB082208B574A83AFF774F617CEBF90@CS1PR8401MB0822.NAMPRD84.PROD.OUTLOOK.COM>
>   "[C-Glib] - writing an extension array" on Thu, 26 Nov 2020 18:11:53 +0000,
>   Ishan Anand <anand.ishan@outlook.com> wrote:
> 
>> Hi
>>
>> How do you go about implementing an extension type through the C API for Arrow?
>>
>> Creating a record batch in python like the example in pyarrow tests [here](https://github.com/apache/arrow/blob/2a5f92455ec4f9788ee96fa209b38d76bd927196/python/pyarrow/tests/test_extension_type.py#L375),
and reading the resulting schema using the C API, it correctly reads it as an array of the
underlying storage type. The schema along with the metadata can be printed as expected.
>> ```
>> ext: int64
>> -- metadata --
>> ARROW:extension:metadata: freq=D
>> ARROW:extension:name: test.period
>> ```
>>
>> However, trying to access the metadata for the schema (obtained with `garrow_schema_get_metadata`)
indicates its size to be 0, which indicates that metadata for the schema isn't the same as
that for a field. Is it possible using the existing API to read/write the metadata for a field?
>>
>>
>> Thank you,
>> Ishan

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