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Fix row::move_as behavior breaking reusability #1145

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Fix row::move_as behavior breaking reusability #1145

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Krzmbrzl
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For the time being, this is merely a sketch of how I think the fix has to work. The current implementation fails at the unavailability of a session object at the row scope...

Once this is finished, this PR fixes #1144

Krzmbrzl
Krzmbrzl commented Apr 21, 2024
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@vadz vadz added this to the 4.1.0 milestone Apr 26, 2024
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Krzmbrzl commented May 1, 2024

@avpalienko could you debug where the SegFault for Oracle is coming from? You seem to have good access to an Oracle installation, whereas for me it is always super tedious to get something to work.

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@avpalienko could you debug where the SegFault for Oracle is coming from? You seem to have good access to an Oracle installation, whereas for me it is always super tedious to get something to work.

I've debugged on windows and have no segfault. But test fails:

BLOB
Blob binding
move_as

D:\CMA\Dev\SOCI\soci_githab\tests\common-tests.h(6784)
...............................................................................

D:\CMA\Dev\SOCI\soci_githab\tests\common-tests.h(6784): FAILED:
{Unknown expression after the reported line}
due to unexpected exception with message:
soci error: Invalid handle while fetching data from "select b from soci_test
where id=:id" with :1=42.

===============================================================================
test cases: 2 | 1 passed | 1 failed
assertions: 162 | 161 passed | 1 failed

I think it's a result of the move_as. Lob locator binds to the statement in define_by_pos():

bbe->reset();
ociData_ = bbe->get_lob_locator();

and then it initialized by OCIDefineByPos(). But in row::move_as() we call dtor ~oracle_blob_backend() with OCIDescriptorFree inside. On the next fetch in the post_fetch we call bbe->set_lob_locator(). Inside it we set locator in the old released value and call OCILobIsOpen which returns OCI_INVALID_HANDLE

@Krzmbrzl
Fix blob fetching semantics in Oracle
f110c69 
Previously, the into-type would take the blob object's LOB locator
object and bind that in the query. That works as long as there is only a
single Blob object being fetched from the database. However, if multiple
values are fetched consecutively, there would only be a single locator
object involved. In the best case, this leads to every new fetch
overriding the previous result and in the worst case, that previous
result has been turned into an independent blob object that has gone out
of scope, which leads to freeing of this shared locator.

With this commit, the into-type object will create its own locator
object and use that. When assigning the fetched result to a blob object,
the locator is copied such that the into-type and the blob keep
independent locator objects, i.e. the locator is no longer shared.
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Krzmbrzl commented Sep 1, 2024 •
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Finally! I think with my latest commit I have found a way to fix the underlying issue 🚀

@avpalienko sorry that I took so long to look into this again. Your debug insights were still very valuable though, so thanks for having taken the time 🙏

@Krzmbrzl Krzmbrzl marked this pull request as ready for review September 1, 2024 07:57
@Krzmbrzl Krzmbrzl requested a review from vadz September 1, 2024 07:57
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vadz approved these changes Sep 3, 2024
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Looks good to me, thanks for fixing this!

Will merge soon.

@vadz vadz mentioned this pull request Sep 3, 2024
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Using row::move_as while iterating rowset yields segmentation fault
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