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Date: Thu, 14 Aug 2008 19:31:15 +1100
From: "=?KOI8-R?B?4czFy9PBzsTSIP7F28XX?=" <alex.cheshev@gmail.com>
To: pgsql-interfaces@postgresql.org
Subject: PostgreSQL arrays and DBD
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Hello.

I create a table:

CREATE TABLE groups (
  group_id serial PRIMARY KEY,
  name varchar(64) UNIQUE NOT NULL,
  guests integer[] DEFAULT '{}'
)

I add a new record to the table:

INSERT INTO groups (name) VALUES ('My friends');

Now the table contains 1 record:

| group_id |    name    | guests
+----------+------------+--------
|        1 | My friends | {}

I read the new record from the table using DBI:

my $sth = $dbh->prepare(qq/SELECT * FROM groups/);
$sth->execute();
my (@guests, $group);
push(@guests, $group) while $group = $sth->fetchrow_hashref(); # Line 4
print $guests[0]->{guests}->[0]; # Why ({group_id=>1, name=>'My friends', *
guests=>[0]*}) ?

Output of the script:

Argument "" isn't numeric in null operation at ./guestmanager.pl line 4
*0*

DBD should return a reference to an empty array. But DBD returned the
reference to the array containing 1 element (0). How can I have a different
result:

({group_id=>1, name=>'My friends', *guests=>[]*})

PS
Version of DBD::Pg is 2.9.0 .

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<div dir="ltr"><div id=":1kp" class="ArwC7c ckChnd"><div dir="ltr"><span style="font-family: courier new,monospace;">Hello.</span><br style="font-family: courier new,monospace;"><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;">I create a table:</span><br style="font-family: courier new,monospace;">
<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">CREATE TABLE groups (</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">&nbsp; group_id serial PRIMARY KEY,</span><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">&nbsp; name varchar(64) UNIQUE NOT NULL,</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">&nbsp; guests integer[] DEFAULT &#39;{}&#39;</span><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">)</span><br style="font-family: courier new,monospace;"><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">I add a new record to the table:</span><br style="font-family: courier new,monospace;">

<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">INSERT INTO groups (name) VALUES (&#39;My friends&#39;);</span><br style="font-family: courier new,monospace;"><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">Now the table contains 1 record:</span><br style="font-family: courier new,monospace;"><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">| group_id |&nbsp;&nbsp;&nbsp; name&nbsp;&nbsp;&nbsp; | guests</span><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">+----------+------------+--------</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 1 | My friends | {}</span><span style="font-family: courier new,monospace;"></span><br style="font-family: courier new,monospace;">

<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">I read the new record from the table using DBI:</span><br style="font-family: courier new,monospace;"><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">my $sth = $dbh-&gt;prepare(qq/SELECT * FROM groups/);</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">$sth-&gt;execute();</span><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">my (@guests, $group);</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">push(@guests, $group) while $group = $sth-&gt;fetchrow_hashref(); # Line 4</span><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">print $guests[0]-&gt;{guests}-&gt;[0]; # Why ({group_id=&gt;1, name=&gt;&#39;My friends&#39;, </span><b style="font-family: courier new,monospace;">guests=&gt;[0]</b><span style="font-family: courier new,monospace;">}) ?</span><br style="font-family: courier new,monospace;">

<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">Output of the script:</span><br style="font-family: courier new,monospace;"><br style="font-family: courier new,monospace;">

<span style="font-family: courier new,monospace;">Argument &quot;&quot; isn&#39;t numeric in null operation at ./guestmanager.pl line 4</span><br style="font-family: courier new,monospace;"><b style="font-family: courier new,monospace;">0</b><br style="font-family: courier new,monospace;">

<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">DBD
should return a reference to an empty array. But DBD returned the
reference to the array containing 1 element (0). How can I have a
different result:</span><br style="font-family: courier new,monospace;">
<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">({group_id=&gt;1, name=&gt;&#39;My friends&#39;, </span><b style="font-family: courier new,monospace;">guests=&gt;[]</b><span style="font-family: courier new,monospace;">})</span><br style="font-family: courier new,monospace;">

<br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">PS</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">Version of DBD::Pg is 2.9.0 .</span></div>

</div></div>

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