On 12/12/2011 11:34, Alex Peshkoff wrote:
> On 12/12/11 15:43, Pierre Y. wrote:
>> Hi All,
>>
>> Thanks to Vlad, we achieved the translation of the FB3 OO API in UIB
>> Components for Delphi.
>>
>> You can checkout the code from SourceForge repository :
>>
>> https://uib.svn.sourceforge.net/svnroot/uib/trunk
>>
>> Now, we only miss hints to deal with FbMessage, it seems that the
>> examples (fbstuff on github) made by Adriano heavily relies on BOOST
>> and as we don't have such possibilities with Delphi we must understand
>> what is exactly an FbMessage and see what we can do.
> I've reordered filed in struct in order to put them in logically correct
> order. [One really present is OK from alignment POV]
>
> struct FbMessage
> {
> unsigned char* buffer; // contains data and NULL flags to
> be transfered to/from engine.
> unsigned int bufferLength; // length of that buffer
> const unsigned char* blr; // describes format of data in a
> form, easily understood by engine
> unsigned int blrLength; // length of that format description
> };
>
> A sample. Imagine you
> create table test (a int, f double precision);
> and after some inserts want to
> select a, f from test;
> Buffer should have following data:
> 4 bytes for integer 'a'
> 2 bytes for it's NULL flag (NULL flag is always 2-byte integer)
> 2 bytes - alignment to 8-bytes boundary for next floating point value,
> unused
> 8 bytes for floating point 'f'
> 2 bytes for it's NULL flag
> Therefore the length of buffer is 18 bytes.
>
> BLR is actually binary language representation for engine. All
> procedures, view, etc. a first translated to BLR. BLR in FbMessage is
> used to transfer data to/from message's buffer. Both BLR generation and
> rules how to align data in buffer correctly can be found in
> src/yvalve/why.cpp, function sqldaParse. Let me not try to repeat that C
> code here in plain english - I'm afraid this can be buggy process :)
>
>
This message requires a BLR more or less as:
unsigned char blr[] = {
blr_version5,
blr_begin,
blr_message, 0,
(2 * 2 /* number of fields */) & 0xFF,
(2 * 2 /* number of fields */) >> 8,
blr_long, 0, /* first field, scale */
blr_short, 0, /* null indicator for first field */
blr_double, /* second field */
blr_short, 0, /* null indicator for second field */
blr_end,
blr_eoc
};
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