Re: ECPG support for struct in INTO list - Mailing list pgsql-hackers

Michael Meskes írta:
> On Wed, Aug 05, 2009 at 11:52:57AM +0200, Boszormenyi Zoltan wrote:
>   
>> This means that what I did in my first patch for this
>> problem in "add_struct_to_head()" (unrolling members
>> of the struct) has to be done in adjust_informix(),
>> turning it into a recursive function.
>> I think this would be a good solution. What do you think?
>>     
>
> No, this doesn't seem right. There should be no need to unroll a struct.
> Instead I would think struct support should be added to the get_var/set_var
> functions. At least that's my guess without really digging into it.
>
> Michael
>   

My question is: why not unroll the struct in the preprocessor?
This adjust_informix() issue aside, if I do this in the same function:
       EXEC SQL BEGIN DECLARE SECTION;       MYTYPE          myvar;       MYNULLTYPE      mynullvar;       EXEC SQL END
DECLARESECTION;
 
       EXEC SQL DECLARE mycur CURSOR FOR SELECT * INTO :myvar
:mynullvar FROM a1;       EXEC SQL OPEN mycur;
       EXEC SQL WHENEVER NOT FOUND DO BREAK;       while (1) {               EXEC SQL FETCH FROM mycur;
...       }
 

then the preprocessed code for DECLARE and FETCH look like below:
       { ECPGdo(__LINE__, 1, 1, NULL, 0, ECPGst_normal, "declare mycur
cursor for select * from a1 where id = 1", ECPGt_EOIT,       ECPGt_int,&(myvar.id),(long)1,(long)1,sizeof(int),
ECPGt_NO_INDICATOR,NULL , 0L, 0L, 0L,       ECPGt_char,&(myvar.t),(long)64,(long)1,(64)*sizeof(char),
ECPGt_NO_INDICATOR,NULL , 0L, 0L, 0L,       ECPGt_double,&(myvar.d1),(long)1,(long)1,sizeof(double),
ECPGt_NO_INDICATOR,NULL , 0L, 0L, 0L,       ECPGt_double,&(myvar.d2),(long)1,(long)1,sizeof(double),
ECPGt_NO_INDICATOR,NULL , 0L, 0L, 0L,       ECPGt_char,&(myvar.c),(long)30,(long)1,(30)*sizeof(char),
ECPGt_NO_INDICATOR,NULL , 0L, 0L, 0L, ECPGt_EORT);
 
#line 39 "test28.pgc"

...
       { ECPGdo(__LINE__, 1, 1, NULL, 0, ECPGst_normal, "fetch from
mycur", ECPGt_EOIT,       ECPGt_int,&(myvar.id),(long)1,(long)1,sizeof(int),       ECPGt_NO_INDICATOR, NULL , 0L, 0L,
0L,      ECPGt_char,&(myvar.t),(long)64,(long)1,(64)*sizeof(char),       ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L,
ECPGt_double,&(myvar.d1),(long)1,(long)1,sizeof(double),      ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L,
ECPGt_double,&(myvar.d2),(long)1,(long)1,sizeof(double),      ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L,
ECPGt_char,&(myvar.c),(long)30,(long)1,(30)*sizeof(char),      ECPGt_NO_INDICATOR, NULL , 0L, 0L, 0L, ECPGt_EORT);
 
#line 43 "test28.pgc"

These are done by ECPGdump_a_struct(), when the struct's members
and their type, size, etc are known. It's unrolled by the ecpg preprocessor.
Your idea about pushing struct support into set_var/get_var seems
not appropriate. With the current set_var scheme, you pass one variable's
properties. Why not keep this simplicity and unroll the struct in the
preprocessor into multiple set_var() calls for simple types?

Best regards,
Zoltán Böszörményi

-- 
Bible has answers for everything. Proof:
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than these cometh of evil." (Matthew 5:37) - basics of digital technology.
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----------------------------------
Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
http://www.postgresql.at/