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From: Teunis Peters <teunis@wintersgift.com>
Subject: Two seperate problems with libpq - arrays and bytea edit
Date: Sat, 14 May 2005 11:40:10 -0700
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I'm trying to figure out how to read from and write to bytea values and 
array (specifically "text[2][]" for a key:value 'dictionary') and 
cannot figure it out.   Arrays I'm completely lost - I haven't a clue 
what the format would be.
bytea - my code segmentation faults.  PQgetlength returns 0.   I don't 
know if I'm putting it in the database correctly.

some sample code.  Yes it's in Objective C.   [db_result] embeds a 
"PGresult" value and does a lot of error checking.  image is of type 
NSData which basically holds binary data.  The rest SHOULD be clear.
I'd provide a smaller example except I'm not yet sure how to create 
console apps in MacOSX...   I suppose I could do it in linux though.

Any advice helpful.   I've been stewing my brain on this for a while 
now and am on something of a time limit.

getValue == PQgetvalue(res,tupple,field)
getlength == PQgetlength(res,tupple,field)
I hope that helps.

commit (subset of full code)
	sprintf(buf, "%i", cat_id);
	paramValues[np] = buf;           paramLen[np] = strlen(buf);    np++;
	paramValues[np] = [image bytes]; paramLen[np] = [image length]; np++;
	PGresult* r;
	r = PQexecParams([conn conn], "UPDATE images SET image = $2 WHERE id = 
$1;",
					 np, NULL, paramValues, paramLen, NULL, 1);
	if (PQresultStatus(r) != PGRES_COMMAND_OK) {
		NSLog(@"UPDATE failed: %s", PQerrorMessage([conn conn]));
	}
	PQclear(r);

access (subset of full code)

	sprintf(buf, "%i", cat_id);
	paramValues[0] = buf;
	res = [db_result alloc];
	[res init:PQexecParams([conn conn], "SELECT image FROM images WHERE id 
= $1",1,NULL,paramValues,NULL,NULL,1)];
	if (!res) return nil;
	if ([res ntuples] < 1) return nil;
	{
		char*     ptr;
		char*     decoded;
		size_t    i, decodedlen;
		NSString* ns;
		ptr = [res getValue:0 field:0];
		if (ptr != NULL) {
			i   = [res getlength:0 field:0];
			decoded = PQunescapeBytea(ptr, &decodedlen);
			image = [[NSData dataWithBytes:decoded length:decodedlen] retain];
			PQfreemem(decoded);
		}
	}

Do I access bytea ("image" is a bytea type) this way, or this way:
		ptr = [res getValue:0 field:0];
		if (ptr != NULL) {
			i   = [res getlength:0 field:0];
			image = [[NSData dataWithBytes:decoded length:i] retain];
		}

--Apple-Mail-1-349856610
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<fixed>I'm trying to figure out how to read from and write to bytea
values and array (specifically "text[2][]" for a key:value
'dictionary') and cannot figure it out.   Arrays I'm completely lost -
I haven't a clue what the format would be.

bytea - my code segmentation faults.  PQgetlength returns 0.   I don't
know if I'm putting it in the database correctly.


some sample code.  Yes it's in Objective C.   [db_result] embeds a
"PGresult" value and does a lot of error checking.  image is of type
NSData which basically holds binary data.  The rest SHOULD be clear.

I'd provide a smaller example except I'm not yet sure how to create
console apps in MacOSX...   I suppose I could do it in linux though.


Any advice helpful.   I've been stewing my brain on this for a while
now and am on something of a time limit.


getValue == PQgetvalue(res,tupple,field)

getlength == PQgetlength(res,tupple,field)

I hope that helps.


commit (subset of full code)

	sprintf(buf, <color><param>8989,1313,1515</param>"%i"</color>,
cat_id);

	paramValues[np] = buf;           paramLen[np] = strlen(buf);    np++;

	paramValues[np] = [image bytes]; paramLen[np] = [image length]; np++;

	PGresult* r;

	r = PQexecParams([conn conn],
<color><param>8989,1313,1515</param>"UPDATE images SET image = $2
WHERE id = $1;"</color>,

					 np, <color><param>7676,0F0F,5050</param>NULL</color>,
paramValues, paramLen,
<color><param>7676,0F0F,5050</param>NULL</color>,
<color><param>0000,0000,FFFF</param>1</color>);

	<color><param>7676,0F0F,5050</param>if</color> (PQresultStatus(r) !=
PGRES_COMMAND_OK) {

		NSLog(<color><param>8989,1313,1515</param>@"UPDATE failed:
%s"</color>, PQerrorMessage([conn conn]));

	}

	PQclear(r);


access (subset of full code)


	sprintf(buf, <color><param>8989,1313,1515</param>"%i"</color>,
cat_id);

	paramValues[<color><param>0000,0000,FFFF</param>0</color>] = buf;

	res = [db_result alloc];

	[res init:PQexecParams([conn conn],
<color><param>8989,1313,1515</param>"SELECT image FROM images WHERE id
= $1"</color>,<color><param>0000,0000,FFFF</param>1</color>,<color><param>7676,0F0F,5050</param>NULL</color>,paramValues,<color><param>7676,0F0F,5050</param>NULL</color>,<color><param>7676,0F0F,5050</param>NULL</color>,<color><param>0000,0000,FFFF</param>1</color>)];

	<color><param>7676,0F0F,5050</param>if</color> (!res)
<color><param>7676,0F0F,5050</param>return</color>
<color><param>7676,0F0F,5050</param>nil</color>;

	<color><param>7676,0F0F,5050</param>if</color> ([res ntuples] <<
<color><param>0000,0000,FFFF</param>1</color>)
<color><param>7676,0F0F,5050</param>return</color>
<color><param>7676,0F0F,5050</param>nil</color>;

	{

		<color><param>7676,0F0F,5050</param>char</color>*     ptr;

		<color><param>7676,0F0F,5050</param>char</color>*     decoded;

		size_t    i, decodedlen;

		NSString* ns;

		ptr = [res getValue:<color><param>0000,0000,FFFF</param>0</color>
field:<color><param>0000,0000,FFFF</param>0</color>];

		<color><param>7676,0F0F,5050</param>if</color> (ptr !=
<color><param>7676,0F0F,5050</param>NULL</color>) {

			i   = [res getlength:<color><param>0000,0000,FFFF</param>0</color>
field:<color><param>0000,0000,FFFF</param>0</color>];

			decoded = PQunescapeBytea(ptr, &decodedlen);

			image = [[NSData dataWithBytes:decoded length:decodedlen] retain];

			PQfreemem(decoded);

		}

	}


Do I access bytea ("image" is a bytea type) this way, or this way:

		ptr = [res getValue:<color><param>0000,0000,FFFE</param>0</color>
field:<color><param>0000,0000,FFFE</param>0</color>];

		<color><param>7675,0F0E,504F</param>if</color> (ptr !=
<color><param>7675,0F0E,504F</param>NULL</color>) {

			i   = [res getlength:<color><param>0000,0000,FFFE</param>0</color>
field:<color><param>0000,0000,FFFE</param>0</color>];

			image = [[NSData dataWithBytes:decoded length:i] retain];

		}

</fixed>
--Apple-Mail-1-349856610--