PApp-SQL/SQL.pm

=head1 NAME

PApp::SQL - absolutely easy yet fast and powerful sql access

=head1 SYNOPSIS

 use PApp::SQL;

 my $st = sql_exec $DBH, "select ... where a = ?", $a;

 local $DBH = <database handle>;
 my $st = sql_exec \my($bind_a, $bind_b), "select a,b ...";
 my $st = sql_insertid
             sql_exec "insert into ... values (?, ?)", $v1, $v2;
 my $a = sql_fetch "select a from ...";
 sql_fetch \my($a, $b), "select a,b ...";

 sql_exists "name from table where name like 'a%'"
    or die "a* required but not existent";

 my $db = new PApp::SQL::Database "", "DBI:mysql:test", "user", "pass";
 local $PApp::SQL::DBH = $db->checked_dbh; # does 'ping'

 sql_exec $db->dbh, "select ...";

=head1 DESCRIPTION

This module provides you with easy-to-use functions to execute sql
commands (using DBI). Despite being easy to use, they are also quite
efficient and allow you to write faster programs in less lines of code. It
should work with anything from perl-5.004_01 onwards, but I only support
5.005+. UTF8 handling (the C<sql_u*> family of functions) will only be
effective with perl version 5.006 and beyond.

If the descriptions here seem terse or if you always wanted to know
what PApp is then have a look at the PApp module which uses this module
extensively but also provides you with a lot more gimmicks to play around
with to help you create cool applications ;)

=cut

package PApp::SQL;

use DBI ();

BEGIN {
   use base qw(Exporter DynaLoader);

   $VERSION = 0.1241;
   @EXPORT = qw(
         sql_exec  sql_fetch  sql_fetchall  sql_exists sql_insertid $sql_exec
         sql_uexec sql_ufetch sql_ufetchall sql_uexists
   );
   @EXPORT_OK = qw(
         connect_cached
   );

   bootstrap PApp::SQL $VERSION;
}

our $sql_exec;  # last result of sql_exec's execute call
our $DBH;       # the default database handle
our $Database;  # the current SQL::Database object, if applicable

our %dbcache;

=head2 GLOBAL VARIABLES

=over 4

=item $sql_exec

Since the C<sql_exec> family of functions return a statement handle there
must eb another way to test the return value of the C<execute> call. This
global variable contains the result of the most recent call to C<execute>
done by this module.

=item $PApp::SQL::DBH

The default database handle used by this module if no C<$DBH> was
specified as argument and no C<$DBH> is found in the current package. See
C<sql_exec> for a discussion.

=item $PApp::SQL::Database

The current default C<PApp::SQL::Database>-object. Future versions might
automatically fall back on this database and create database handles from
it if neccessary. At the moment this is not used by this module but might
be nice as a placeholder for the database object that corresponds to
$PApp::SQL::DBH.

=back

=head2 FUNCTIONS

=over 4

=item $dbh = connect_cached $id, $dsn, $user, $pass, $flags, $connect

(not exported by by default)

Connect to the database given by C<($dsn,$user,$pass)>, while using the
flags from C<$flags>. These are just the same arguments as given to
C<DBI->connect>.

The database handle will be cached under the unique id
C<$id|$dsn|$user|$pass>. If the same id is requested later, the
cached handle will be checked (using ping), and the connection will
be re-established if necessary (be sure to prefix your application or
module name to the id to make it "more" unique. Things like __PACKAGE__ .
__LINE__ work fine as well).

The reason C<$id> is necessary is that you might specify special connect
arguments or special flags, or you might want to configure your $DBH
differently than maybe other applications requesting the same database
connection. If none of this is becessary for your application you can
leave $id empty (i.e. "").

If specified, C<$connect> is a callback (e.g. a coderef) that will be
called each time a new connection is being established, with the new
C<$dbh> as first argument.

Examples:

 # try your luck opening the papp database without access info
 $dbh = connect_cached __FILE__, "DBI:mysql:papp";

Mysql-specific behaviour: The default setting of mysql_client_found_rows
is TRUE, you can overwrite this, though.

=cut

sub connect_cached {
   my ($id, $dsn, $user, $pass, $flags, $connect) = @_;
   # the following line is duplicated in PApp::SQL::Database::new
   $id = "$id\0$dsn\0$user\0$pass";
   unless ($dbcache{$id} && $dbcache{$id}->ping) {
      # first, nuke our statement cache (sooory ;)
      cachesize cachesize 0;

      # then make mysql behave more standardly by default
      $dsn =~ /^[Dd][Bb][Ii]:mysql:/
         and $dsn !~ /;mysql_client_found_rows/
            and $dsn .= ";mysql_client_found_rows=1";

      # then connect anew
      $dbcache{$id} =
         eval { DBI->connect($dsn, $user, $pass, $flags) }
         || eval { DBI->connect($dsn, $user, $pass, $flags) }
         || die "unable to connect to database $dsn: $DBI::errstr\n";
      $connect->($dbcache{$id}) if $connect;
   }
   $dbcache{$id};
}

=item $sth = sql_exec [dbh,] [bind-vals...,] "sql-statement", [arguments...]

=item $sth = sql_uexec <see sql_exec>

C<sql_exec> is the most important and most-used function in this module.

Runs the given sql command with the given parameters and returns the
statement handle. The command and the statement handle will be cached
(with the database handle and the sql string as key), so prepare will be
called only once for each distinct sql call (please keep in mind that the
returned statement will always be the same, so, if you call C<sql_exec>
with the same dbh and sql-statement twice (e.g. in a subroutine you
called), the statement handle for the first call mustn't be used.

The database handle (the first argument) is optional. If it is missing,
C<sql_exec> first tries to use the variable C<$DBH> in the current (=
calling) package and, if that fails, it tries to use database handle in
C<$PApp::SQL::DBH>, which you can set before calling these functions.

The actual return value from the C<$sth->execute> call is stored in the
package-global (and exported) variable C<$sql_exec>.

If any error occurs C<sql_exec> will throw an exception.

C<sql_uexec> is similar to C<sql_exec> but upgrades all input arguments to
utf8 before calling the C<execute> method.

Examples:

 # easy one
 my $st = sql_exec "select name, id from table where id = ?", $id;
 while (my ($name, $id) = $st->fetchrow_array) { ... };

 # the fastest way to use dbi, using bind_columns
 my $st = sql_exec \my($name, $id),
                   "select name, id from table where id = ?",
                   $id;
 while ($st->fetch) { ...}

 # now use a different dastabase:
 sql_exec $dbh, "update file set name = ?", "oops.txt";


=item sql_fetch <see sql_exec>

=item sql_ufetch <see sql_uexec>

Execute an sql-statement and fetch the first row of results. Depending on
the caller context the row will be returned as a list (array context), or
just the first columns. In table form:

 CONTEXT        RESULT
 void           ()
 scalar         first column
 list           array

C<sql_fetch> is quite efficient in conjunction with bind variables:

 sql_fetch \my($name, $amount),
           "select name, amount from table where id name  = ?",
           "Toytest";

But of course the normal way to call it is simply:

 my($name, $amount) = sql_fetch "select ...", args...

... and it's still quite fast unless you fetch large amounts of data.

C<sql_ufetch> is similar to C<sql_fetch> but upgrades all input values to
utf8 and forces all result values to utf8.

=item sql_fetchall <see sql_exec>

=item sql_ufetchall <see sql_uexec>

Similarly to C<sql_fetch>, but all result rows will be fetched (this is
of course inefficient for large results!). The context is ignored (only
list context makes sense), but the result still depends on the number of
columns in the result:

 COLUMNS        RESULT
 0              ()
 1              (row1, row2, row3...)
 many           ([row1], [row2], [row3]...)

Examples (all of which are inefficient):

 for (sql_fetchall "select id from table") { ... }

 my @names = sql_fetchall "select name from user";

 for (sql_fetchall "select name, age, place from user") {
    my ($name, $age, $place) = @$_;
 }

C<sql_ufetchall> is similar to C<sql_fetchall> but upgrades all input
values to utf8 and forces all result values to utf8.

=item sql_exists "<table> where ...", args...

=item sql_uexists <see sql_exists>

Check wether the result of the sql-statement "select xxx from
$first_argument" would be empty or not (that is, imagine the string
"select * from" were prepended to your statement (it isn't)). Should work
with every database but can be quite slow, except on mysql, where this
should be quite fast.

C<sql_uexists> is similar to C<sql_exists> but upgrades all parameters to
utf8.

Examples:

 print "user 7 exists!\n"
    if sql_exists "user where id = ?", 7;
 
 die "duplicate key"
    if sql_exists "user where name = ? and pass = ?", "stefan", "geheim";

=cut

=item $lastid = sql_insertid $sth

Returns the last automatically created key value. It must be executed
directly after executing the insert statement that created it. This is
what is actually returned for various databases. If your database is
missing, please send me an e-mail on how to implement this ;)

 mysql:    first C<AUTO_INCREMENT> column set to NULL
 postgres: C<oid> column (is there a way to get the last SERIAL?)
 sybase:   C<IDENTITY> column of the last insert (slow)
 informix: C<SERIAL> or C<SERIAL8> column of the last insert

Except for sybase, this does not require a server access.

=cut

sub sql_insertid($) {
   my $sth = shift or die "sql_insertid requires a statement handle";
   my $dbh = $sth->{Database};
   my $driver = $dbh->{Driver}{Name};

   $driver eq "mysql"    and return $sth->{mysql_insertid};
   $driver eq "Pg"       and return $sth->{pg_oid_status};
   $driver eq "Sybase"   and return sql_fetch($dbh, 'SELECT @@IDENTITY');
   $driver eq "Informix" and return $sth->{ix_sqlerrd}[1];

   die "sql_insertid does not spport the dbd driver '$driver', please see PApp::SQL::sql_insertid";
}

=item [old-size] = cachesize [new-size]

Returns (and possibly changes) the LRU cache size used by C<sql_exec>. The
default is somewhere around 50 (= the 50 last recently used statements
will be cached). It shouldn't be too large, since a simple linear listed
is used for the cache at the moment (which, for small (<100) cache sizes
is actually quite fast).

The function always returns the cache size in effect I<before> the call,
so, to nuke the cache (for example, when a database connection has died
or you want to garbage collect old database/statement handles), this
construct can be used:

 PApp::SQL::cachesize PApp::SQL::cachesize 0;

=cut

=item reinitialize [not exported]

Clears any internal caches (statement cache, database handle
cache). Should be called after C<fork> and other accidents that invalidate
database handles.

=cut

sub reinitialize {
   cachesize cachesize 0;
   for (values %dbcache) {
      eval { $_->{InactiveDestroy} = 1 };
   }
   undef %dbcache;
}

=back

=cut

reinitialize;

package PApp::SQL::Database;

=head2 THE DATABASE CLASS

Again (sigh) the problem of persistency. What do you do when you have
to serialize on object that contains (or should contain) a database
handle? Short answer: you don't. Long answer: you can embed the necessary
information to recreate the dbh when needed.

The C<PApp::SQL::Database> class does that, in a relatively efficient
fashion: the overhead is currently a single method call per access (you
can cache the real dbh if you want).

=over 4

=item $db = new <same arguments as C<connect_cached>>

The C<new> call takes the same arguments as C<connect_cached> (obviously,
if you supply a connect callback it better is serializable, see
L<PApp::Callback>!) and returns a serializable database class. No database
handle is actually being created.

=item $db->dbh

Return the database handle as fast as possible (usually just a hash lookup).

=item $db->checked_dbh

Return the database handle, but first check that the database is still
available and re-open the connection if necessary.

=cut

sub new($$;@) {
   my $class = shift;
   my ($id, $dsn, $user, $pass, $flags, $connect) = @_;
   # the following line is duplicated in PApp::SQL::Database::new
   my $id2 = "$id\0$dsn\0$user\0$pass";
   bless [$id2, $flags, $connect], $class;
}

# the following two functions better be fast!
sub dbh($) {
   $dbcache{$_[0][0]} || $_[0]->checked_dbh;
}

sub checked_dbh($) {
   my $dbh = $dbcache{$_[0][0]};
   $dbh && $dbh->ping
      ? $dbh
      : PApp::SQL::connect_cached((split /\x00/, $_[0][0]), $_[0][1], $_[0][2]);
}

=item $db->dsn

Return the DSN (L<DBI>) fo the database object (e.g. for error messages).

=item $db->login

Return the login name.

=item $db->password

Return the password (emphasizing the fact that the apssword is stored plaintext ;)

=cut

sub dsn($) {
   my $self = shift;
   (split /\x00/, $self->[0])[1];
}

sub login($) {
   my $self = shift;
   (split /\x00/, $self->[0])[2];
}

sub password($) {
   my $self = shift;
   (split /\x00/, $self->[0])[3];
}

=back

=cut

1;

=head1 SEE ALSO

L<PApp>.

=head1 AUTHOR

 Marc Lehmann <pcg@goof.com>
 http://www.goof.com/pcg/marc/

=cut

Revision:	1.18
Committed:	Mon Dec 31 03:01:49 2001 UTC (22 years, 4 months ago) by root
Branch:	MAIN
Changes since 1.17:	+10 -2 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			PApp::SQL - absolutely easy yet fast and powerful sql access
4
5			=head1 SYNOPSIS
6
7			use PApp::SQL;
8	root	1.10
9			my $st = sql_exec $DBH, "select ... where a = ?", $a;
10
11			local $DBH = <database handle>;
12			my $st = sql_exec \my($bind_a, $bind_b), "select a,b ...";
13			my $st = sql_insertid
14			sql_exec "insert into ... values (?, ?)", $v1, $v2;
15			my $a = sql_fetch "select a from ...";
16			sql_fetch \my($a, $b), "select a,b ...";
17
18			sql_exists "name from table where name like 'a%'"
19			or die "a* required but not existent";
20
21			my $db = new PApp::SQL::Database "", "DBI:mysql:test", "user", "pass";
22			local $PApp::SQL::DBH = $db->checked_dbh; # does 'ping'
23
24			sql_exec $db->dbh, "select ...";
25	root	1.1
26			=head1 DESCRIPTION
27
28			This module provides you with easy-to-use functions to execute sql
29			commands (using DBI). Despite being easy to use, they are also quite
30	root	1.10	efficient and allow you to write faster programs in less lines of code. It
31			should work with anything from perl-5.004_01 onwards, but I only support
32	root	1.15	5.005+. UTF8 handling (the C<sql_u*> family of functions) will only be
33			effective with perl version 5.006 and beyond.
34	root	1.10
35			If the descriptions here seem terse or if you always wanted to know
36			what PApp is then have a look at the PApp module which uses this module
37			extensively but also provides you with a lot more gimmicks to play around
38			with to help you create cool applications ;)
39	root	1.1
40			=cut
41
42			package PApp::SQL;
43
44	root	1.10	use DBI ();
45	root	1.1
46			BEGIN {
47	root	1.10	use base qw(Exporter DynaLoader);
48	root	1.1
49	root	1.18	$VERSION = 0.1241;
50	root	1.1	@EXPORT = qw(
51	root	1.16	sql_exec sql_fetch sql_fetchall sql_exists sql_insertid $sql_exec
52			sql_uexec sql_ufetch sql_ufetchall sql_uexists
53	root	1.1	);
54			@EXPORT_OK = qw(
55			connect_cached
56			);
57
58	root	1.10	bootstrap PApp::SQL $VERSION;
59	root	1.1	}
60
61			our $sql_exec; # last result of sql_exec's execute call
62			our $DBH; # the default database handle
63	root	1.10	our $Database; # the current SQL::Database object, if applicable
64	root	1.1
65			our %dbcache;
66
67	root	1.10	=head2 GLOBAL VARIABLES
68
69			=over 4
70
71			=item $sql_exec
72
73			Since the C<sql_exec> family of functions return a statement handle there
74			must eb another way to test the return value of the C<execute> call. This
75			global variable contains the result of the most recent call to C<execute>
76			done by this module.
77
78			=item $PApp::SQL::DBH
79
80			The default database handle used by this module if no C<$DBH> was
81			specified as argument and no C<$DBH> is found in the current package. See
82			C<sql_exec> for a discussion.
83
84			=item $PApp::SQL::Database
85
86			The current default C<PApp::SQL::Database>-object. Future versions might
87			automatically fall back on this database and create database handles from
88			it if neccessary. At the moment this is not used by this module but might
89			be nice as a placeholder for the database object that corresponds to
90			$PApp::SQL::DBH.
91
92			=back
93
94			=head2 FUNCTIONS
95
96			=over 4
97
98	root	1.1	=item $dbh = connect_cached $id, $dsn, $user, $pass, $flags, $connect
99
100			(not exported by by default)
101
102			Connect to the database given by C<($dsn,$user,$pass)>, while using the
103			flags from C<$flags>. These are just the same arguments as given to
104			C<DBI->connect>.
105
106	root	1.6	The database handle will be cached under the unique id
107			C<$id\|$dsn\|$user\|$pass>. If the same id is requested later, the
108			cached handle will be checked (using ping), and the connection will
109			be re-established if necessary (be sure to prefix your application or
110			module name to the id to make it "more" unique. Things like __PACKAGE__ .
111			__LINE__ work fine as well).
112
113			The reason C<$id> is necessary is that you might specify special connect
114			arguments or special flags, or you might want to configure your $DBH
115			differently than maybe other applications requesting the same database
116			connection. If none of this is becessary for your application you can
117			leave $id empty (i.e. "").
118	root	1.1
119			If specified, C<$connect> is a callback (e.g. a coderef) that will be
120			called each time a new connection is being established, with the new
121			C<$dbh> as first argument.
122
123			Examples:
124
125			# try your luck opening the papp database without access info
126			$dbh = connect_cached __FILE__, "DBI:mysql:papp";
127
128	root	1.18	Mysql-specific behaviour: The default setting of mysql_client_found_rows
129			is TRUE, you can overwrite this, though.
130
131	root	1.1	=cut
132
133			sub connect_cached {
134			my ($id, $dsn, $user, $pass, $flags, $connect) = @_;
135			# the following line is duplicated in PApp::SQL::Database::new
136			$id = "$id\0$dsn\0$user\0$pass";
137			unless ($dbcache{$id} && $dbcache{$id}->ping) {
138	root	1.5	# first, nuke our statement cache (sooory ;)
139	root	1.1	cachesize cachesize 0;
140	root	1.18
141			# then make mysql behave more standardly by default
142			$dsn =~ /^[Dd][Bb][Ii]:mysql:/
143			and $dsn !~ /;mysql_client_found_rows/
144			and $dsn .= ";mysql_client_found_rows=1";
145
146	root	1.1	# then connect anew
147			$dbcache{$id} =
148			eval { DBI->connect($dsn, $user, $pass, $flags) }
149			\|\| eval { DBI->connect($dsn, $user, $pass, $flags) }
150	root	1.5	\|\| die "unable to connect to database $dsn: $DBI::errstr\n";
151	root	1.1	$connect->($dbcache{$id}) if $connect;
152			}
153			$dbcache{$id};
154			}
155
156			=item $sth = sql_exec [dbh,] [bind-vals...,] "sql-statement", [arguments...]
157
158	root	1.15	=item $sth = sql_uexec <see sql_exec>
159
160	root	1.1	C<sql_exec> is the most important and most-used function in this module.
161
162			Runs the given sql command with the given parameters and returns the
163			statement handle. The command and the statement handle will be cached
164			(with the database handle and the sql string as key), so prepare will be
165			called only once for each distinct sql call (please keep in mind that the
166			returned statement will always be the same, so, if you call C<sql_exec>
167			with the same dbh and sql-statement twice (e.g. in a subroutine you
168			called), the statement handle for the first call mustn't be used.
169
170			The database handle (the first argument) is optional. If it is missing,
171			C<sql_exec> first tries to use the variable C<$DBH> in the current (=
172			calling) package and, if that fails, it tries to use database handle in
173			C<$PApp::SQL::DBH>, which you can set before calling these functions.
174
175			The actual return value from the C<$sth->execute> call is stored in the
176			package-global (and exported) variable C<$sql_exec>.
177
178			If any error occurs C<sql_exec> will throw an exception.
179
180	root	1.15	C<sql_uexec> is similar to C<sql_exec> but upgrades all input arguments to
181			utf8 before calling the C<execute> method.
182
183	root	1.1	Examples:
184
185			# easy one
186			my $st = sql_exec "select name, id from table where id = ?", $id;
187			while (my ($name, $id) = $st->fetchrow_array) { ... };
188
189			# the fastest way to use dbi, using bind_columns
190			my $st = sql_exec \my($name, $id),
191			"select name, id from table where id = ?",
192			$id;
193			while ($st->fetch) { ...}
194
195			# now use a different dastabase:
196			sql_exec $dbh, "update file set name = ?", "oops.txt";
197
198
199			=item sql_fetch <see sql_exec>
200
201	root	1.15	=item sql_ufetch <see sql_uexec>
202
203			Execute an sql-statement and fetch the first row of results. Depending on
204	root	1.1	the caller context the row will be returned as a list (array context), or
205			just the first columns. In table form:
206
207			CONTEXT RESULT
208			void ()
209			scalar first column
210			list array
211
212			C<sql_fetch> is quite efficient in conjunction with bind variables:
213
214			sql_fetch \my($name, $amount),
215			"select name, amount from table where id name = ?",
216			"Toytest";
217
218			But of course the normal way to call it is simply:
219
220			my($name, $amount) = sql_fetch "select ...", args...
221
222			... and it's still quite fast unless you fetch large amounts of data.
223
224	root	1.15	C<sql_ufetch> is similar to C<sql_fetch> but upgrades all input values to
225			utf8 and forces all result values to utf8.
226
227	root	1.1	=item sql_fetchall <see sql_exec>
228
229	root	1.15	=item sql_ufetchall <see sql_uexec>
230
231	root	1.1	Similarly to C<sql_fetch>, but all result rows will be fetched (this is
232			of course inefficient for large results!). The context is ignored (only
233			list context makes sense), but the result still depends on the number of
234			columns in the result:
235
236			COLUMNS RESULT
237			0 ()
238			1 (row1, row2, row3...)
239			many ([row1], [row2], [row3]...)
240
241			Examples (all of which are inefficient):
242
243			for (sql_fetchall "select id from table") { ... }
244
245			my @names = sql_fetchall "select name from user";
246
247			for (sql_fetchall "select name, age, place from user") {
248			my ($name, $age, $place) = @$_;
249			}
250
251	root	1.15	C<sql_ufetchall> is similar to C<sql_fetchall> but upgrades all input
252			values to utf8 and forces all result values to utf8.
253
254	root	1.1	=item sql_exists "<table> where ...", args...
255
256	root	1.15	=item sql_uexists <see sql_exists>
257
258	root	1.1	Check wether the result of the sql-statement "select xxx from
259			$first_argument" would be empty or not (that is, imagine the string
260	root	1.13	"select * from" were prepended to your statement (it isn't)). Should work
261	root	1.1	with every database but can be quite slow, except on mysql, where this
262			should be quite fast.
263
264	root	1.15	C<sql_uexists> is similar to C<sql_exists> but upgrades all parameters to
265			utf8.
266
267	root	1.1	Examples:
268
269			print "user 7 exists!\n"
270			if sql_exists "user where id = ?", 7;
271
272			die "duplicate key"
273			if sql_exists "user where name = ? and pass = ?", "stefan", "geheim";
274
275			=cut
276
277	root	1.3	=item $lastid = sql_insertid $sth
278
279	root	1.8	Returns the last automatically created key value. It must be executed
280			directly after executing the insert statement that created it. This is
281			what is actually returned for various databases. If your database is
282			missing, please send me an e-mail on how to implement this ;)
283
284			mysql: first C<AUTO_INCREMENT> column set to NULL
285			postgres: C<oid> column (is there a way to get the last SERIAL?)
286			sybase: C<IDENTITY> column of the last insert (slow)
287			informix: C<SERIAL> or C<SERIAL8> column of the last insert
288
289			Except for sybase, this does not require a server access.
290	root	1.3
291			=cut
292
293			sub sql_insertid($) {
294			my $sth = shift or die "sql_insertid requires a statement handle";
295			my $dbh = $sth->{Database};
296			my $driver = $dbh->{Driver}{Name};
297
298	root	1.8	$driver eq "mysql" and return $sth->{mysql_insertid};
299			$driver eq "Pg" and return $sth->{pg_oid_status};
300			$driver eq "Sybase" and return sql_fetch($dbh, 'SELECT @@IDENTITY');
301	root	1.3	$driver eq "Informix" and return $sth->{ix_sqlerrd}[1];
302
303			die "sql_insertid does not spport the dbd driver '$driver', please see PApp::SQL::sql_insertid";
304	root	1.1	}
305
306			=item [old-size] = cachesize [new-size]
307
308			Returns (and possibly changes) the LRU cache size used by C<sql_exec>. The
309			default is somewhere around 50 (= the 50 last recently used statements
310			will be cached). It shouldn't be too large, since a simple linear listed
311			is used for the cache at the moment (which, for small (<100) cache sizes
312			is actually quite fast).
313
314			The function always returns the cache size in effect I<before> the call,
315			so, to nuke the cache (for example, when a database connection has died
316			or you want to garbage collect old database/statement handles), this
317			construct can be used:
318
319			PApp::SQL::cachesize PApp::SQL::cachesize 0;
320
321			=cut
322
323			=item reinitialize [not exported]
324
325	root	1.9	Clears any internal caches (statement cache, database handle
326			cache). Should be called after C<fork> and other accidents that invalidate
327			database handles.
328	root	1.1
329			=cut
330
331			sub reinitialize {
332			cachesize cachesize 0;
333			for (values %dbcache) {
334	root	1.11	eval { $_->{InactiveDestroy} = 1 };
335	root	1.1	}
336			undef %dbcache;
337			}
338
339			=back
340
341			=cut
342
343	root	1.7	reinitialize;
344
345	root	1.1	package PApp::SQL::Database;
346
347			=head2 THE DATABASE CLASS
348
349	root	1.15	Again (sigh) the problem of persistency. What do you do when you have
350			to serialize on object that contains (or should contain) a database
351			handle? Short answer: you don't. Long answer: you can embed the necessary
352			information to recreate the dbh when needed.
353	root	1.1
354			The C<PApp::SQL::Database> class does that, in a relatively efficient
355			fashion: the overhead is currently a single method call per access (you
356			can cache the real dbh if you want).
357
358			=over 4
359
360			=item $db = new <same arguments as C<connect_cached>>
361
362			The C<new> call takes the same arguments as C<connect_cached> (obviously,
363			if you supply a connect callback it better is serializable, see
364			L<PApp::Callback>!) and returns a serializable database class. No database
365			handle is actually being created.
366
367			=item $db->dbh
368
369			Return the database handle as fast as possible (usually just a hash lookup).
370
371			=item $db->checked_dbh
372
373			Return the database handle, but first check that the database is still
374			available and re-open the connection if necessary.
375
376			=cut
377
378			sub new($$;@) {
379			my $class = shift;
380			my ($id, $dsn, $user, $pass, $flags, $connect) = @_;
381			# the following line is duplicated in PApp::SQL::Database::new
382			my $id2 = "$id\0$dsn\0$user\0$pass";
383			bless [$id2, $flags, $connect], $class;
384			}
385
386			# the following two functions better be fast!
387			sub dbh($) {
388			$dbcache{$_[0][0]} \|\| $_[0]->checked_dbh;
389			}
390
391			sub checked_dbh($) {
392			my $dbh = $dbcache{$_[0][0]};
393			$dbh && $dbh->ping
394			? $dbh
395			: PApp::SQL::connect_cached((split /\x00/, $_[0][0]), $_[0][1], $_[0][2]);
396			}
397
398			=item $db->dsn
399
400			Return the DSN (L<DBI>) fo the database object (e.g. for error messages).
401
402	root	1.14	=item $db->login
403
404			Return the login name.
405
406			=item $db->password
407
408			Return the password (emphasizing the fact that the apssword is stored plaintext ;)
409
410	root	1.1	=cut
411
412			sub dsn($) {
413			my $self = shift;
414	root	1.9	(split /\x00/, $self->[0])[1];
415	root	1.14	}
416
417			sub login($) {
418			my $self = shift;
419			(split /\x00/, $self->[0])[2];
420			}
421
422			sub password($) {
423			my $self = shift;
424			(split /\x00/, $self->[0])[3];
425	root	1.1	}
426
427			=back
428
429			=cut
430
431			1;
432
433			=head1 SEE ALSO
434
435			L<PApp>.
436
437			=head1 AUTHOR
438
439			Marc Lehmann <pcg@goof.com>
440			http://www.goof.com/pcg/marc/
441
442			=cut
443