Re: [sqlite] Error code for VT xColumn()/xRowid() if row does not exist?

2016-12-13 Thread Hick Gunter 
xRowid() is only called if the (hidden field) rowid is explicitly mentioned in 
the select list, join condition or where clause(s) of a SELECT statement; or if 
your VTAB supports write operations (see xUpdate documentation 
http://www.sqlite.org/vtab.html#the_xupdate_method ).

-Ursprüngliche Nachricht-
Von: sqlite-users [mailto:sqlite-users-boun...@mailinglists.sqlite.org] Im 
Auftrag von Bob Friesenhahn
Gesendet: Montag, 12. Dezember 2016 20:50
An: SQLite mailing list 
Betreff: Re: [sqlite] Error code for VT xColumn()/xRowid() if row does not 
exist?

On Tue, 13 Dec 2016, Dan Kennedy wrote:
>>
>> Perhaps SQLITE_NOTFOUND is a correct return code, but the
>> documentation does not address return codes from virtual table modules.
>>
>> What is the correct code to return?  If a cursor is being navigated,
>> then I would prefer that the cursor continue to the next result row.
>
> If you want the query to continue, the virtual table methods must
> return SQLITE_OK. Anything else will cause SQLite to abandon the query
> and return the error to the user. Have the xColumn() method return
> NULL in this case I guess.

Ok, thanks.

> Or you could load all the column values into memory when your virtual
> table cursor visits each row of the underlying data. Then you wouldn't
> have to handle the current row disappearing on you.

We are normally doing column caching as you describe.  Even without the caching 
I can lock for column access at the row level.  The case where the row might no 
longer exist is for xRowid(), but this function does not seem to be called for 
the table I am looking at.

Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,http://www.GraphicsMagick.org/
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 Gunter Hick
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Tel: +43 1 80100 0
E-Mail: h...@scigames.at

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Re: [sqlite] Error code for VT xColumn()/xRowid() if row does not exist?

2016-12-13 Thread Hick Gunter 
>On 12/13/2016 01:47 AM, Bob Friesenhahn wrote:
>> I am reworking code for a virtual table module and need to provide
>> proper error codes from the xColumn() and xRowid() callbacks for the
>> case where the row id does not exist, or the current row goes away.
>> This problem occurs because the current virtual table module
>> implementation does not lock for its entire access (a matter for
>> subsequent investigation).
>>
>> The documentation just says to "return an appropriate error code".
>>
>> Perhaps SQLITE_NOTFOUND is a correct return code, but the
>> documentation does not address return codes from virtual table modules.
>>
>> What is the correct code to return?  If a cursor is being navigated,
>> then I would prefer that the cursor continue to the next result row.
>
>If you want the query to continue, the virtual table methods must return 
>SQLITE_OK. Anything else will cause SQLite to abandon the query and return the 
>error to the user. Have the xColumn() method return NULL >in this case I guess.
>
>Or you could load all the column values into memory when your virtual table 
>cursor visits each row of the underlying data. Then you wouldn't have to 
>handle the current row disappearing on you.
>
I second this suggestion. Unless your underlying data store is (possibly 
shared) memory that may have already been clobbered, keeping a copy of the row 
"as seen when xFilter()/xNext() was called" avoids this problem.


___
 Gunter Hick
Software Engineer
Scientific Games International GmbH
FN 157284 a, HG Wien
Klitschgasse 2-4, A-1130 Vienna, Austria
Tel: +43 1 80100 0
E-Mail: h...@scigames.at

This communication (including any attachments) is intended for the use of the 
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communication is strictly prohibited. If you have received this communication 
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Re: [sqlite] Error code for VT xColumn()/xRowid() if row does not exist?

2016-12-13 Thread Hick Gunter 
Current documentation http://www.sqlite.org/rescode.html suggests you return 
(267) SQLITE_CORRUPT_VTAB in this case. Other candidates would be SQLITE_IOERR 
or SQLITE_NOTFOUND.

You may also call one or more of the sqlite_result_error() functions to set an 
error string and/or an error code; current documentation 
http://www.sqlite.org/vtab.html#the_xcolumn_method suggests you set the error 
text by calling one of the sqlite_result_text() functions and returning the 
error code.

If your intention is to silently skip the row, you should refrain from calling 
any of the sqlite_result() functions (or explicitly call sqlite_result_null()) 
to set a NULL column value and return SQLITE_OK. You just have to hope that a 
row containing one or more (or even all) "fake" NULL values does not wreck your 
statement.


-Ursprüngliche Nachricht-
Von: sqlite-users [mailto:sqlite-users-boun...@mailinglists.sqlite.org] Im 
Auftrag von Bob Friesenhahn
Gesendet: Montag, 12. Dezember 2016 19:48
An: SQLite mailing list 
Betreff: [sqlite] Error code for VT xColumn()/xRowid() if row does not exist?

I am reworking code for a virtual table module and need to provide proper error 
codes from the xColumn() and xRowid() callbacks for the case where the row id 
does not exist, or the current row goes away.
This problem occurs because the current virtual table module implementation 
does not lock for its entire access (a matter for subsequent investigation).

The documentation just says to "return an appropriate error code".

Perhaps SQLITE_NOTFOUND is a correct return code, but the documentation does 
not address return codes from virtual table modules.

What is the correct code to return?  If a cursor is being navigated, then I 
would prefer that the cursor continue to the next result row.

Thanks,

Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,http://www.GraphicsMagick.org/
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___
 Gunter Hick
Software Engineer
Scientific Games International GmbH
FN 157284 a, HG Wien
Klitschgasse 2-4, A-1130 Vienna, Austria
Tel: +43 1 80100 0
E-Mail: h...@scigames.at

This communication (including any attachments) is intended for the use of the 
intended recipient(s) only and may contain information that is confidential, 
privileged or legally protected. Any unauthorized use or dissemination of this 
communication is strictly prohibited. If you have received this communication 
in error, please immediately notify the sender by return e-mail message and 
delete all copies of the original communication. Thank you for your cooperation.


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Re: [sqlite] Error code for VT xColumn()/xRowid() if row does not exist?

2016-12-12 Thread Bob Friesenhahn 

On Tue, 13 Dec 2016, Dan Kennedy wrote:


Perhaps SQLITE_NOTFOUND is a correct return code, but the documentation 
does not address return codes from virtual table modules.


What is the correct code to return?  If a cursor is being navigated, then I 
would prefer that the cursor continue to the next result row.


If you want the query to continue, the virtual table methods must return 
SQLITE_OK. Anything else will cause SQLite to abandon the query and return 
the error to the user. Have the xColumn() method return NULL in this case I 
guess.


Ok, thanks.

Or you could load all the column values into memory when your virtual table 
cursor visits each row of the underlying data. Then you wouldn't have to 
handle the current row disappearing on you.


We are normally doing column caching as you describe.  Even without 
the caching I can lock for column access at the row level.  The case 
where the row might no longer exist is for xRowid(), but this function 
does not seem to be called for the table I am looking at.


Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,http://www.GraphicsMagick.org/
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Re: [sqlite] Error code for VT xColumn()/xRowid() if row does not exist?

2016-12-12 Thread Dan Kennedy 

On 12/13/2016 01:47 AM, Bob Friesenhahn wrote:
I am reworking code for a virtual table module and need to provide 
proper error codes from the xColumn() and xRowid() callbacks for the 
case where the row id does not exist, or the current row goes away. 
This problem occurs because the current virtual table module 
implementation does not lock for its entire access (a matter for 
subsequent investigation).


The documentation just says to "return an appropriate error code".

Perhaps SQLITE_NOTFOUND is a correct return code, but the 
documentation does not address return codes from virtual table modules.


What is the correct code to return?  If a cursor is being navigated, 
then I would prefer that the cursor continue to the next result row.


If you want the query to continue, the virtual table methods must return 
SQLITE_OK. Anything else will cause SQLite to abandon the query and 
return the error to the user. Have the xColumn() method return NULL in 
this case I guess.


Or you could load all the column values into memory when your virtual 
table cursor visits each row of the underlying data. Then you wouldn't 
have to handle the current row disappearing on you.


Dan.




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[sqlite] Error code for VT xColumn()/xRowid() if row does not exist?

2016-12-12 Thread Bob Friesenhahn 
I am reworking code for a virtual table module and need to provide 
proper error codes from the xColumn() and xRowid() callbacks for the 
case where the row id does not exist, or the current row goes away. 
This problem occurs because the current virtual table module 
implementation does not lock for its entire access (a matter for 
subsequent investigation).


The documentation just says to "return an appropriate error code".

Perhaps SQLITE_NOTFOUND is a correct return code, but the 
documentation does not address return codes from virtual table 
modules.


What is the correct code to return?  If a cursor is being navigated, 
then I would prefer that the cursor continue to the next result row.


Thanks,

Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,http://www.GraphicsMagick.org/
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