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+.

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 = 0.12;
   @EXPORT = qw(
         sql_exec sql_fetch sql_fetchall sql_exists sql_insertid $sql_exec
   );
   @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";

=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) {
      #warn "connecting to ($dsn|$user|$pass|$flags)\n";#d#
      # first, nuke our statement cache (sooory ;)
      cachesize cachesize 0;
      # 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...]

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.

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>

Execute a 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.

=item sql_fetchall <see sql_exec>

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, $place) = @$_;
 }

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

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.

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 { $_->disconnect };
   }
   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).

=cut

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

=back

=cut

1;

=head1 SEE ALSO

L<PApp>.

=head1 AUTHOR

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

=cut

Revision:	1.10
Committed:	Mon Feb 5 14:05:08 2001 UTC (23 years, 3 months ago) by root
Branch:	MAIN
Changes since 1.9:	+61 -20 lines
Log Message:	* empty log message *
#	Content
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
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
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	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	5.005+.
33
34	If the descriptions here seem terse or if you always wanted to know
35	what PApp is then have a look at the PApp module which uses this module
36	extensively but also provides you with a lot more gimmicks to play around
37	with to help you create cool applications ;)
38
39	=cut
40
41	package PApp::SQL;
42
43	use DBI ();
44
45	BEGIN {
46	use base qw(Exporter DynaLoader);
47
48	$VERSION = 0.12;
49	@EXPORT = qw(
50	sql_exec sql_fetch sql_fetchall sql_exists sql_insertid $sql_exec
51	);
52	@EXPORT_OK = qw(
53	connect_cached
54	);
55
56	bootstrap PApp::SQL $VERSION;
57	}
58
59	our $sql_exec; # last result of sql_exec's execute call
60	our $DBH; # the default database handle
61	our $Database; # the current SQL::Database object, if applicable
62
63	our %dbcache;
64
65	=head2 GLOBAL VARIABLES
66
67	=over 4
68
69	=item $sql_exec
70
71	Since the C<sql_exec> family of functions return a statement handle there
72	must eb another way to test the return value of the C<execute> call. This
73	global variable contains the result of the most recent call to C<execute>
74	done by this module.
75
76	=item $PApp::SQL::DBH
77
78	The default database handle used by this module if no C<$DBH> was
79	specified as argument and no C<$DBH> is found in the current package. See
80	C<sql_exec> for a discussion.
81
82	=item $PApp::SQL::Database
83
84	The current default C<PApp::SQL::Database>-object. Future versions might
85	automatically fall back on this database and create database handles from
86	it if neccessary. At the moment this is not used by this module but might
87	be nice as a placeholder for the database object that corresponds to
88	$PApp::SQL::DBH.
89
90	=back
91
92	=head2 FUNCTIONS
93
94	=over 4
95
96	=item $dbh = connect_cached $id, $dsn, $user, $pass, $flags, $connect
97
98	(not exported by by default)
99
100	Connect to the database given by C<($dsn,$user,$pass)>, while using the
101	flags from C<$flags>. These are just the same arguments as given to
102	C<DBI->connect>.
103
104	The database handle will be cached under the unique id
105	C<$id\|$dsn\|$user\|$pass>. If the same id is requested later, the
106	cached handle will be checked (using ping), and the connection will
107	be re-established if necessary (be sure to prefix your application or
108	module name to the id to make it "more" unique. Things like __PACKAGE__ .
109	__LINE__ work fine as well).
110
111	The reason C<$id> is necessary is that you might specify special connect
112	arguments or special flags, or you might want to configure your $DBH
113	differently than maybe other applications requesting the same database
114	connection. If none of this is becessary for your application you can
115	leave $id empty (i.e. "").
116
117	If specified, C<$connect> is a callback (e.g. a coderef) that will be
118	called each time a new connection is being established, with the new
119	C<$dbh> as first argument.
120
121	Examples:
122
123	# try your luck opening the papp database without access info
124	$dbh = connect_cached __FILE__, "DBI:mysql:papp";
125
126	=cut
127
128	sub connect_cached {
129	my ($id, $dsn, $user, $pass, $flags, $connect) = @_;
130	# the following line is duplicated in PApp::SQL::Database::new
131	$id = "$id\0$dsn\0$user\0$pass";
132	unless ($dbcache{$id} && $dbcache{$id}->ping) {
133	#warn "connecting to ($dsn\|$user\|$pass\|$flags)\n";#d#
134	# first, nuke our statement cache (sooory ;)
135	cachesize cachesize 0;
136	# then connect anew
137	$dbcache{$id} =
138	eval { DBI->connect($dsn, $user, $pass, $flags) }
139	\|\| eval { DBI->connect($dsn, $user, $pass, $flags) }
140	\|\| die "unable to connect to database $dsn: $DBI::errstr\n";
141	$connect->($dbcache{$id}) if $connect;
142	}
143	$dbcache{$id};
144	}
145
146	=item $sth = sql_exec [dbh,] [bind-vals...,] "sql-statement", [arguments...]
147
148	C<sql_exec> is the most important and most-used function in this module.
149
150	Runs the given sql command with the given parameters and returns the
151	statement handle. The command and the statement handle will be cached
152	(with the database handle and the sql string as key), so prepare will be
153	called only once for each distinct sql call (please keep in mind that the
154	returned statement will always be the same, so, if you call C<sql_exec>
155	with the same dbh and sql-statement twice (e.g. in a subroutine you
156	called), the statement handle for the first call mustn't be used.
157
158	The database handle (the first argument) is optional. If it is missing,
159	C<sql_exec> first tries to use the variable C<$DBH> in the current (=
160	calling) package and, if that fails, it tries to use database handle in
161	C<$PApp::SQL::DBH>, which you can set before calling these functions.
162
163	The actual return value from the C<$sth->execute> call is stored in the
164	package-global (and exported) variable C<$sql_exec>.
165
166	If any error occurs C<sql_exec> will throw an exception.
167
168	Examples:
169
170	# easy one
171	my $st = sql_exec "select name, id from table where id = ?", $id;
172	while (my ($name, $id) = $st->fetchrow_array) { ... };
173
174	# the fastest way to use dbi, using bind_columns
175	my $st = sql_exec \my($name, $id),
176	"select name, id from table where id = ?",
177	$id;
178	while ($st->fetch) { ...}
179
180	# now use a different dastabase:
181	sql_exec $dbh, "update file set name = ?", "oops.txt";
182
183
184	=item sql_fetch <see sql_exec>
185
186	Execute a sql-statement and fetch the first row of results. Depending on
187	the caller context the row will be returned as a list (array context), or
188	just the first columns. In table form:
189
190	CONTEXT RESULT
191	void ()
192	scalar first column
193	list array
194
195	C<sql_fetch> is quite efficient in conjunction with bind variables:
196
197	sql_fetch \my($name, $amount),
198	"select name, amount from table where id name = ?",
199	"Toytest";
200
201	But of course the normal way to call it is simply:
202
203	my($name, $amount) = sql_fetch "select ...", args...
204
205	... and it's still quite fast unless you fetch large amounts of data.
206
207	=item sql_fetchall <see sql_exec>
208
209	Similarly to C<sql_fetch>, but all result rows will be fetched (this is
210	of course inefficient for large results!). The context is ignored (only
211	list context makes sense), but the result still depends on the number of
212	columns in the result:
213
214	COLUMNS RESULT
215	0 ()
216	1 (row1, row2, row3...)
217	many ([row1], [row2], [row3]...)
218
219	Examples (all of which are inefficient):
220
221	for (sql_fetchall "select id from table") { ... }
222
223	my @names = sql_fetchall "select name from user";
224
225	for (sql_fetchall "select name, age, place from user") {
226	my ($name, $age, $place) = @$_;
227	}
228
229	=item sql_exists "<table> where ...", args...
230
231	Check wether the result of the sql-statement "select xxx from
232	$first_argument" would be empty or not (that is, imagine the string
233	"select from" were prepended to your statement (it isn't)). Should work
234	with every database but can be quite slow, except on mysql, where this
235	should be quite fast.
236
237	Examples:
238
239	print "user 7 exists!\n"
240	if sql_exists "user where id = ?", 7;
241
242	die "duplicate key"
243	if sql_exists "user where name = ? and pass = ?", "stefan", "geheim";
244
245	=cut
246
247	=item $lastid = sql_insertid $sth
248
249	Returns the last automatically created key value. It must be executed
250	directly after executing the insert statement that created it. This is
251	what is actually returned for various databases. If your database is
252	missing, please send me an e-mail on how to implement this ;)
253
254	mysql: first C<AUTO_INCREMENT> column set to NULL
255	postgres: C<oid> column (is there a way to get the last SERIAL?)
256	sybase: C<IDENTITY> column of the last insert (slow)
257	informix: C<SERIAL> or C<SERIAL8> column of the last insert
258
259	Except for sybase, this does not require a server access.
260
261	=cut
262
263	sub sql_insertid($) {
264	my $sth = shift or die "sql_insertid requires a statement handle";
265	my $dbh = $sth->{Database};
266	my $driver = $dbh->{Driver}{Name};
267
268	$driver eq "mysql" and return $sth->{mysql_insertid};
269	$driver eq "Pg" and return $sth->{pg_oid_status};
270	$driver eq "Sybase" and return sql_fetch($dbh, 'SELECT @@IDENTITY');
271	$driver eq "Informix" and return $sth->{ix_sqlerrd}[1];
272
273	die "sql_insertid does not spport the dbd driver '$driver', please see PApp::SQL::sql_insertid";
274	}
275
276	=item [old-size] = cachesize [new-size]
277
278	Returns (and possibly changes) the LRU cache size used by C<sql_exec>. The
279	default is somewhere around 50 (= the 50 last recently used statements
280	will be cached). It shouldn't be too large, since a simple linear listed
281	is used for the cache at the moment (which, for small (<100) cache sizes
282	is actually quite fast).
283
284	The function always returns the cache size in effect I<before> the call,
285	so, to nuke the cache (for example, when a database connection has died
286	or you want to garbage collect old database/statement handles), this
287	construct can be used:
288
289	PApp::SQL::cachesize PApp::SQL::cachesize 0;
290
291	=cut
292
293	=item reinitialize [not exported]
294
295	Clears any internal caches (statement cache, database handle
296	cache). Should be called after C<fork> and other accidents that invalidate
297	database handles.
298
299	=cut
300
301	sub reinitialize {
302	cachesize cachesize 0;
303	for (values %dbcache) {
304	eval { $_->disconnect };
305	}
306	undef %dbcache;
307	}
308
309	=back
310
311	=cut
312
313	reinitialize;
314
315	package PApp::SQL::Database;
316
317	=head2 THE DATABASE CLASS
318
319	Again (sigh) the problem of persistency. What do you do when you have to serialize on object
320	that contains (or should contain) a database handle? Short answer: you don't. Long answer:
321	you can embed the necessary information to recreate the dbh when needed.
322
323	The C<PApp::SQL::Database> class does that, in a relatively efficient
324	fashion: the overhead is currently a single method call per access (you
325	can cache the real dbh if you want).
326
327	=over 4
328
329	=item $db = new <same arguments as C<connect_cached>>
330
331	The C<new> call takes the same arguments as C<connect_cached> (obviously,
332	if you supply a connect callback it better is serializable, see
333	L<PApp::Callback>!) and returns a serializable database class. No database
334	handle is actually being created.
335
336	=item $db->dbh
337
338	Return the database handle as fast as possible (usually just a hash lookup).
339
340	=item $db->checked_dbh
341
342	Return the database handle, but first check that the database is still
343	available and re-open the connection if necessary.
344
345	=cut
346
347	sub new($$;@) {
348	my $class = shift;
349	my ($id, $dsn, $user, $pass, $flags, $connect) = @_;
350	# the following line is duplicated in PApp::SQL::Database::new
351	my $id2 = "$id\0$dsn\0$user\0$pass";
352	bless [$id2, $flags, $connect], $class;
353	}
354
355	# the following two functions better be fast!
356	sub dbh($) {
357	$dbcache{$_[0][0]} \|\| $_[0]->checked_dbh;
358	}
359
360	sub checked_dbh($) {
361	my $dbh = $dbcache{$_[0][0]};
362	$dbh && $dbh->ping
363	? $dbh
364	: PApp::SQL::connect_cached((split /\x00/, $_[0][0]), $_[0][1], $_[0][2]);
365	}
366
367	=item $db->dsn
368
369	Return the DSN (L<DBI>) fo the database object (e.g. for error messages).
370
371	=cut
372
373	sub dsn($) {
374	my $self = shift;
375	(split /\x00/, $self->[0])[1];
376	}
377
378	=back
379
380	=cut
381
382	1;
383
384	=head1 SEE ALSO
385
386	L<PApp>.
387
388	=head1 AUTHOR
389
390	Marc Lehmann <pcg@goof.com>
391	http://www.goof.com/pcg/marc/
392
393	=cut
394