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=head1 NAME |
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|
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PApp::SQL - absolutely easy yet fast and powerful sql access |
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|
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=head1 SYNOPSIS |
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|
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use PApp::SQL; |
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# to be written |
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|
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=head1 DESCRIPTION |
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|
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This module provides you with easy-to-use functions to execute sql |
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commands (using DBI). Despite being easy to use, they are also quite |
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efficient and allow you to write faster programs in less lines of code. |
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|
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=over 4 |
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|
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=cut |
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|
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package PApp::SQL; |
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|
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use DBI; |
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|
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#use PApp::Exception; # not yet used |
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|
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BEGIN { |
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use base Exporter; |
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|
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$VERSION = 0.1; |
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@EXPORT = qw( |
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sql_exec sql_fetch sql_fetchall sql_exists sql_insertid $sql_exec |
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); |
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@EXPORT_OK = qw( |
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connect_cached |
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); |
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|
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require XSLoader; |
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XSLoader::load PApp::SQL, $VERSION; |
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} |
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|
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our $sql_exec; # last result of sql_exec's execute call |
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our $DBH; # the default database handle |
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our $database; # the current SQL::Database object, if applicable |
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|
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our %dbcache; |
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|
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=item $dbh = connect_cached $id, $dsn, $user, $pass, $flags, $connect |
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|
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(not exported by by default) |
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|
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Connect to the database given by C<($dsn,$user,$pass)>, while using the |
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flags from C<$flags>. These are just the same arguments as given to |
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C<DBI->connect>. |
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|
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The database handle will be cached under the unique id C<$id>. If the same |
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id is requested later, the cached handle will be checked (using ping), and |
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the connection will be re-established if necessary (be sure to prefix your |
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application or module name to the id to make it "more" unique. Things like |
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__PACKAGE__ . __LINE__ work fine as well). |
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|
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If specified, C<$connect> is a callback (e.g. a coderef) that will be |
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called each time a new connection is being established, with the new |
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C<$dbh> as first argument. |
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|
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Examples: |
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|
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# try your luck opening the papp database without access info |
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$dbh = connect_cached __FILE__, "DBI:mysql:papp"; |
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|
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=cut |
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|
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sub connect_cached { |
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my ($id, $dsn, $user, $pass, $flags, $connect) = @_; |
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# the following line is duplicated in PApp::SQL::Database::new |
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$id = "$id\0$dsn\0$user\0$pass"; |
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unless ($dbcache{$id} && $dbcache{$id}->ping) { |
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#warn "connecting to ($dsn|$user|$pass|$flags)\n";#d# |
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# first, nuke our cache (sooory ;) |
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cachesize cachesize 0; |
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# then connect anew |
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$dbcache{$id} = |
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eval { DBI->connect($dsn, $user, $pass, $flags) } |
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|| eval { DBI->connect($dsn, $user, $pass, $flags) } |
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|| die "$DBI::errstr\n"; |
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$connect->($dbcache{$id}) if $connect; |
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} |
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$dbcache{$id}; |
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} |
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|
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=item $sth = sql_exec [dbh,] [bind-vals...,] "sql-statement", [arguments...] |
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|
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C<sql_exec> is the most important and most-used function in this module. |
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Runs the given sql command with the given parameters and returns the |
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statement handle. The command and the statement handle will be cached |
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(with the database handle and the sql string as key), so prepare will be |
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called only once for each distinct sql call (please keep in mind that the |
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returned statement will always be the same, so, if you call C<sql_exec> |
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with the same dbh and sql-statement twice (e.g. in a subroutine you |
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called), the statement handle for the first call mustn't be used. |
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|
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The database handle (the first argument) is optional. If it is missing, |
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C<sql_exec> first tries to use the variable C<$DBH> in the current (= |
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calling) package and, if that fails, it tries to use database handle in |
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C<$PApp::SQL::DBH>, which you can set before calling these functions. |
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|
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The actual return value from the C<$sth->execute> call is stored in the |
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package-global (and exported) variable C<$sql_exec>. |
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|
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If any error occurs C<sql_exec> will throw an exception. |
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|
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Examples: |
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# easy one |
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my $st = sql_exec "select name, id from table where id = ?", $id; |
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while (my ($name, $id) = $st->fetchrow_array) { ... }; |
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|
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# the fastest way to use dbi, using bind_columns |
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my $st = sql_exec \my($name, $id), |
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"select name, id from table where id = ?", |
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$id; |
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while ($st->fetch) { ...} |
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|
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# now use a different dastabase: |
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sql_exec $dbh, "update file set name = ?", "oops.txt"; |
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|
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=item sql_fetch <see sql_exec> |
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Execute a sql-statement and fetch the first row of results. Depending on |
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the caller context the row will be returned as a list (array context), or |
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just the first columns. In table form: |
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|
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CONTEXT RESULT |
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void () |
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scalar first column |
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list array |
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C<sql_fetch> is quite efficient in conjunction with bind variables: |
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sql_fetch \my($name, $amount), |
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"select name, amount from table where id name = ?", |
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"Toytest"; |
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|
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But of course the normal way to call it is simply: |
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my($name, $amount) = sql_fetch "select ...", args... |
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|
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... and it's still quite fast unless you fetch large amounts of data. |
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|
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=item sql_fetchall <see sql_exec> |
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|
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Similarly to C<sql_fetch>, but all result rows will be fetched (this is |
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of course inefficient for large results!). The context is ignored (only |
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list context makes sense), but the result still depends on the number of |
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columns in the result: |
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|
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COLUMNS RESULT |
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0 () |
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1 (row1, row2, row3...) |
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many ([row1], [row2], [row3]...) |
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|
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Examples (all of which are inefficient): |
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for (sql_fetchall "select id from table") { ... } |
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my @names = sql_fetchall "select name from user"; |
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for (sql_fetchall "select name, age, place from user") { |
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my ($name, $age, $place) = @$_; |
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} |
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=item sql_exists "<table> where ...", args... |
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Check wether the result of the sql-statement "select xxx from |
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$first_argument" would be empty or not (that is, imagine the string |
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"select from" were prepended to your statement (it isn't)). Should work |
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with every database but can be quite slow, except on mysql, where this |
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should be quite fast. |
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|
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Examples: |
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print "user 7 exists!\n" |
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if sql_exists "user where id = ?", 7; |
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die "duplicate key" |
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if sql_exists "user where name = ? and pass = ?", "stefan", "geheim"; |
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|
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=cut |
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|
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# uncodumented, since unportable (only works with DBH even!). yet it is exported (aaargh!) |
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sub sql_insertid { |
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$DBH->{mysql_insertid}; |
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} |
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=item [old-size] = cachesize [new-size] |
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Returns (and possibly changes) the LRU cache size used by C<sql_exec>. The |
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default is somewhere around 50 (= the 50 last recently used statements |
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will be cached). It shouldn't be too large, since a simple linear listed |
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is used for the cache at the moment (which, for small (<100) cache sizes |
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is actually quite fast). |
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|
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The function always returns the cache size in effect I<before> the call, |
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so, to nuke the cache (for example, when a database connection has died |
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or you want to garbage collect old database/statement handles), this |
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construct can be used: |
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PApp::SQL::cachesize PApp::SQL::cachesize 0; |
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|
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=cut |
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|
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=item reinitialize [not exported] |
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Clears any internal caches (statement cache, database handle cache). |
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=cut |
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sub reinitialize { |
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cachesize cachesize 0; |
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for (values %dbcache) { |
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eval { $_->disconnect }; |
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} |
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undef %dbcache; |
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} |
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|
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=back |
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|
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=cut |
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|
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package PApp::SQL::Database; |
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|
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=head2 THE DATABASE CLASS |
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Again (sigh) the problem of persistency. What do you do when you have to serialize on object |
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that contains (or should contain) a database handle? Short answer: you don't. Long answer: |
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you can embed the necessary information to recreate the dbh when needed. |
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The C<PApp::SQL::Database> class does that, in a relatively efficient |
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fashion: the overhead is currently a single method call per access (you |
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can cache the real dbh if you want). |
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|
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=over 4 |
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|
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=item $db = new <same arguments as C<connect_cached>> |
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|
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The C<new> call takes the same arguments as C<connect_cached> (obviously, |
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if you supply a connect callback it better is serializable, see |
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L<PApp::Callback>!) and returns a serializable database class. No database |
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handle is actually being created. |
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|
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=item $db->dbh |
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|
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Return the database handle as fast as possible (usually just a hash lookup). |
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|
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=item $db->checked_dbh |
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Return the database handle, but first check that the database is still |
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available and re-open the connection if necessary. |
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|
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=cut |
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|
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sub new($$;@) { |
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my $class = shift; |
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my ($id, $dsn, $user, $pass, $flags, $connect) = @_; |
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# the following line is duplicated in PApp::SQL::Database::new |
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my $id2 = "$id\0$dsn\0$user\0$pass"; |
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bless [$id2, $flags, $connect], $class; |
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} |
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|
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# the following two functions better be fast! |
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sub dbh($) { |
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$dbcache{$_[0][0]} || $_[0]->checked_dbh; |
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} |
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|
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sub checked_dbh($) { |
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my $dbh = $dbcache{$_[0][0]}; |
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$dbh && $dbh->ping |
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? $dbh |
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: PApp::SQL::connect_cached((split /\x00/, $_[0][0]), $_[0][1], $_[0][2]); |
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} |
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|
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=item $db->dsn |
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|
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Return the DSN (L<DBI>) fo the database object (e.g. for error messages). |
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|
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=cut |
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|
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sub dsn($) { |
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my $self = shift; |
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$self->[1][1]; |
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} |
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|
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=back |
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|
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=cut |
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|
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reinitialize; |
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|
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1; |
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|
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=head1 BUGS |
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|
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As of this writing, sql_fetch and sql_fetchall are not very well tested |
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(they were just re-written in C). |
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|
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sql_exists could be faster (it is written very ugly to not change the |
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current package). |
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|
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=head1 SEE ALSO |
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|
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L<PApp>. |
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|
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=head1 AUTHOR |
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|
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Marc Lehmann <pcg@goof.com> |
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http://www.goof.com/pcg/marc/ |
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|
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=cut |
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|
