PApp-SQL/SQL.pm

=head1 NAME

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

=head1 SYNOPSIS

 use PApp::SQL;
 # to be written

=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.

=over 4

=cut

package PApp::SQL;

use DBI;

#use PApp::Exception; # not yet used

BEGIN {
   use base Exporter;

   $VERSION = 0.11;
   @EXPORT = qw(
         sql_exec sql_fetch sql_fetchall sql_exists sql_insertid $sql_exec
   );
   @EXPORT_OK = qw(
         connect_cached
   );

   require XSLoader;
   XSLoader::load 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;

=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>. 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).

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 (e.g. for mysql
AUTO_INCREMENT or sybase IDENTITY fields). It must be executed directly
after executing the insert statement that created it.

=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};
   $driver eq "Sybase" and return sql_fetch($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).

=cut

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

=back

=cut

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;
   $self->[1][1];
}

=back

=cut

reinitialize;

1;

=head1 BUGS

As of this writing, sql_fetch and sql_fetchall are not very well tested
(they were just re-written in C).

sql_exists could be faster (it is written very ugly to not change the
current package).

=head1 SEE ALSO

L<PApp>.

=head1 AUTHOR

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

=cut

Revision:	1.5
Committed:	Sat Jan 6 03:04:03 2001 UTC (23 years, 4 months ago) by root
Branch:	MAIN
Changes since 1.4:	+2 -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			# to be written
9
10			=head1 DESCRIPTION
11
12			This module provides you with easy-to-use functions to execute sql
13			commands (using DBI). Despite being easy to use, they are also quite
14			efficient and allow you to write faster programs in less lines of code.
15
16			=over 4
17
18			=cut
19
20			package PApp::SQL;
21
22			use DBI;
23
24			#use PApp::Exception; # not yet used
25
26			BEGIN {
27			use base Exporter;
28
29	root	1.4	$VERSION = 0.11;
30	root	1.1	@EXPORT = qw(
31			sql_exec sql_fetch sql_fetchall sql_exists sql_insertid $sql_exec
32			);
33			@EXPORT_OK = qw(
34			connect_cached
35			);
36
37			require XSLoader;
38			XSLoader::load PApp::SQL, $VERSION;
39			}
40
41			our $sql_exec; # last result of sql_exec's execute call
42			our $DBH; # the default database handle
43			our $database; # the current SQL::Database object, if applicable
44
45			our %dbcache;
46
47			=item $dbh = connect_cached $id, $dsn, $user, $pass, $flags, $connect
48
49			(not exported by by default)
50
51			Connect to the database given by C<($dsn,$user,$pass)>, while using the
52			flags from C<$flags>. These are just the same arguments as given to
53			C<DBI->connect>.
54
55			The database handle will be cached under the unique id C<$id>. If the same
56			id is requested later, the cached handle will be checked (using ping), and
57			the connection will be re-established if necessary (be sure to prefix your
58			application or module name to the id to make it "more" unique. Things like
59			__PACKAGE__ . __LINE__ work fine as well).
60
61			If specified, C<$connect> is a callback (e.g. a coderef) that will be
62			called each time a new connection is being established, with the new
63			C<$dbh> as first argument.
64
65			Examples:
66
67			# try your luck opening the papp database without access info
68			$dbh = connect_cached __FILE__, "DBI:mysql:papp";
69
70			=cut
71
72			sub connect_cached {
73			my ($id, $dsn, $user, $pass, $flags, $connect) = @_;
74			# the following line is duplicated in PApp::SQL::Database::new
75			$id = "$id\0$dsn\0$user\0$pass";
76			unless ($dbcache{$id} && $dbcache{$id}->ping) {
77			#warn "connecting to ($dsn\|$user\|$pass\|$flags)\n";#d#
78	root	1.5	# first, nuke our statement cache (sooory ;)
79	root	1.1	cachesize cachesize 0;
80			# then connect anew
81			$dbcache{$id} =
82			eval { DBI->connect($dsn, $user, $pass, $flags) }
83			\|\| eval { DBI->connect($dsn, $user, $pass, $flags) }
84	root	1.5	\|\| die "unable to connect to database $dsn: $DBI::errstr\n";
85	root	1.1	$connect->($dbcache{$id}) if $connect;
86			}
87			$dbcache{$id};
88			}
89
90			=item $sth = sql_exec [dbh,] [bind-vals...,] "sql-statement", [arguments...]
91
92			C<sql_exec> is the most important and most-used function in this module.
93
94			Runs the given sql command with the given parameters and returns the
95			statement handle. The command and the statement handle will be cached
96			(with the database handle and the sql string as key), so prepare will be
97			called only once for each distinct sql call (please keep in mind that the
98			returned statement will always be the same, so, if you call C<sql_exec>
99			with the same dbh and sql-statement twice (e.g. in a subroutine you
100			called), the statement handle for the first call mustn't be used.
101
102			The database handle (the first argument) is optional. If it is missing,
103			C<sql_exec> first tries to use the variable C<$DBH> in the current (=
104			calling) package and, if that fails, it tries to use database handle in
105			C<$PApp::SQL::DBH>, which you can set before calling these functions.
106
107			The actual return value from the C<$sth->execute> call is stored in the
108			package-global (and exported) variable C<$sql_exec>.
109
110			If any error occurs C<sql_exec> will throw an exception.
111
112			Examples:
113
114			# easy one
115			my $st = sql_exec "select name, id from table where id = ?", $id;
116			while (my ($name, $id) = $st->fetchrow_array) { ... };
117
118			# the fastest way to use dbi, using bind_columns
119			my $st = sql_exec \my($name, $id),
120			"select name, id from table where id = ?",
121			$id;
122			while ($st->fetch) { ...}
123
124			# now use a different dastabase:
125			sql_exec $dbh, "update file set name = ?", "oops.txt";
126
127
128			=item sql_fetch <see sql_exec>
129
130			Execute a sql-statement and fetch the first row of results. Depending on
131			the caller context the row will be returned as a list (array context), or
132			just the first columns. In table form:
133
134			CONTEXT RESULT
135			void ()
136			scalar first column
137			list array
138
139			C<sql_fetch> is quite efficient in conjunction with bind variables:
140
141			sql_fetch \my($name, $amount),
142			"select name, amount from table where id name = ?",
143			"Toytest";
144
145			But of course the normal way to call it is simply:
146
147			my($name, $amount) = sql_fetch "select ...", args...
148
149			... and it's still quite fast unless you fetch large amounts of data.
150
151			=item sql_fetchall <see sql_exec>
152
153			Similarly to C<sql_fetch>, but all result rows will be fetched (this is
154			of course inefficient for large results!). The context is ignored (only
155			list context makes sense), but the result still depends on the number of
156			columns in the result:
157
158			COLUMNS RESULT
159			0 ()
160			1 (row1, row2, row3...)
161			many ([row1], [row2], [row3]...)
162
163			Examples (all of which are inefficient):
164
165			for (sql_fetchall "select id from table") { ... }
166
167			my @names = sql_fetchall "select name from user";
168
169			for (sql_fetchall "select name, age, place from user") {
170			my ($name, $age, $place) = @$_;
171			}
172
173			=item sql_exists "<table> where ...", args...
174
175			Check wether the result of the sql-statement "select xxx from
176			$first_argument" would be empty or not (that is, imagine the string
177			"select from" were prepended to your statement (it isn't)). Should work
178			with every database but can be quite slow, except on mysql, where this
179			should be quite fast.
180
181			Examples:
182
183			print "user 7 exists!\n"
184			if sql_exists "user where id = ?", 7;
185
186			die "duplicate key"
187			if sql_exists "user where name = ? and pass = ?", "stefan", "geheim";
188
189			=cut
190
191	root	1.3	=item $lastid = sql_insertid $sth
192
193			Returns the last automatically created key value (e.g. for mysql
194			AUTO_INCREMENT or sybase IDENTITY fields). It must be executed directly
195			after executing the insert statement that created it.
196
197			=cut
198
199			sub sql_insertid($) {
200			my $sth = shift or die "sql_insertid requires a statement handle";
201			my $dbh = $sth->{Database};
202			my $driver = $dbh->{Driver}{Name};
203
204			$driver eq "mysql" and return $sth->{mysql_insertid};
205			$driver eq "Sybase" and return sql_fetch($dbh, 'SELECT @@IDENTITY');
206			$driver eq "Informix" and return $sth->{ix_sqlerrd}[1];
207
208			die "sql_insertid does not spport the dbd driver '$driver', please see PApp::SQL::sql_insertid";
209	root	1.1	}
210
211			=item [old-size] = cachesize [new-size]
212
213			Returns (and possibly changes) the LRU cache size used by C<sql_exec>. The
214			default is somewhere around 50 (= the 50 last recently used statements
215			will be cached). It shouldn't be too large, since a simple linear listed
216			is used for the cache at the moment (which, for small (<100) cache sizes
217			is actually quite fast).
218
219			The function always returns the cache size in effect I<before> the call,
220			so, to nuke the cache (for example, when a database connection has died
221			or you want to garbage collect old database/statement handles), this
222			construct can be used:
223
224			PApp::SQL::cachesize PApp::SQL::cachesize 0;
225
226			=cut
227
228			=item reinitialize [not exported]
229
230			Clears any internal caches (statement cache, database handle cache).
231
232			=cut
233
234			sub reinitialize {
235			cachesize cachesize 0;
236			for (values %dbcache) {
237			eval { $_->disconnect };
238			}
239			undef %dbcache;
240			}
241
242			=back
243
244			=cut
245
246			package PApp::SQL::Database;
247
248			=head2 THE DATABASE CLASS
249
250			Again (sigh) the problem of persistency. What do you do when you have to serialize on object
251			that contains (or should contain) a database handle? Short answer: you don't. Long answer:
252			you can embed the necessary information to recreate the dbh when needed.
253
254			The C<PApp::SQL::Database> class does that, in a relatively efficient
255			fashion: the overhead is currently a single method call per access (you
256			can cache the real dbh if you want).
257
258			=over 4
259
260			=item $db = new <same arguments as C<connect_cached>>
261
262			The C<new> call takes the same arguments as C<connect_cached> (obviously,
263			if you supply a connect callback it better is serializable, see
264			L<PApp::Callback>!) and returns a serializable database class. No database
265			handle is actually being created.
266
267			=item $db->dbh
268
269			Return the database handle as fast as possible (usually just a hash lookup).
270
271			=item $db->checked_dbh
272
273			Return the database handle, but first check that the database is still
274			available and re-open the connection if necessary.
275
276			=cut
277
278			sub new($$;@) {
279			my $class = shift;
280			my ($id, $dsn, $user, $pass, $flags, $connect) = @_;
281			# the following line is duplicated in PApp::SQL::Database::new
282			my $id2 = "$id\0$dsn\0$user\0$pass";
283			bless [$id2, $flags, $connect], $class;
284			}
285
286			# the following two functions better be fast!
287			sub dbh($) {
288			$dbcache{$_[0][0]} \|\| $_[0]->checked_dbh;
289			}
290
291			sub checked_dbh($) {
292			my $dbh = $dbcache{$_[0][0]};
293			$dbh && $dbh->ping
294			? $dbh
295			: PApp::SQL::connect_cached((split /\x00/, $_[0][0]), $_[0][1], $_[0][2]);
296			}
297
298			=item $db->dsn
299
300			Return the DSN (L<DBI>) fo the database object (e.g. for error messages).
301
302			=cut
303
304			sub dsn($) {
305			my $self = shift;
306			$self->[1][1];
307			}
308
309			=back
310
311			=cut
312
313			reinitialize;
314
315			1;
316
317			=head1 BUGS
318
319			As of this writing, sql_fetch and sql_fetchall are not very well tested
320			(they were just re-written in C).
321
322			sql_exists could be faster (it is written very ugly to not change the
323			current package).
324
325			=head1 SEE ALSO
326
327			L<PApp>.
328
329			=head1 AUTHOR
330
331			Marc Lehmann <pcg@goof.com>
332			http://www.goof.com/pcg/marc/
333
334			=cut
335