Marc Lehmann > PApp-SQL-2.0 > PApp::SQL

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NAME ^

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

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 $id = 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 "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 ...";

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 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 ;)

Global Variables

$sql_exec

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

$PApp::SQL::DBH

The default database handle used by this module if no $DBH was specified as argument. See sql_exec for a discussion.

$PApp::SQL::Database

The current default 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.

Functions

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

(not exported by by default)

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

The database handle will be cached under the unique id $id|$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 $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 necessary for your application you can leave $id empty (i.e. "").

If specified, $connect is a callback (e.g. a coderef) that will be called each time a new connection is being established, with the new $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.

$sth = sql_exec [dbh,] [bind-vals...,] "sql-statement", [arguments...]
$sth = sql_uexec <see sql_exec>

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 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 not be in use anymore, as the subsequent call will re-use the handle.

The database handle (the first argument) is optional. If it is missing, it tries to use database handle in $PApp::SQL::DBH, which you can set before calling these functions. NOTICE: future and former versions of PApp::SQL might also look up the global variable $DBH in the callers package.

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

If any error occurs sql_exec will throw an exception.

sql_uexec is similar to sql_exec but upgrades all input arguments to UTF-8 before calling the 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";
sql_fetch <see sql_exec>
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

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.

sql_ufetch is similar to sql_fetch but upgrades all input values to UTF-8 and forces all result values to UTF-8 (this does not include result parameters, only return values. Using bind variables in conjunction with sql_u* functions might result in undefined behaviour - we use UTF-8 on bind-variables at execution time and it seems to work on DBD::mysql as it ignores the UTF-8 bit completely. Which just means that that DBD-driver is broken).

sql_fetchall <see sql_exec>
sql_ufetchall <see sql_uexec>

Similarly to 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, $place) = @$_;
 }

sql_ufetchall is similar to sql_fetchall but upgrades all input values to UTF-8 and forces all result values to UTF-8 (see the caveats in the description of sql_ufetch, though).

sql_exists "<table_references> where <where_condition>...", args...
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.

sql_uexists is similar to sql_exists but upgrades all parameters to UTF-8.

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";
$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
 sqlite:   C<last_insert_rowid()>

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

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

Returns (and possibly changes) the LRU cache size used by 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 list 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 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;
reinitialize [not exported]

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

Type Deduction

Since every database driver seems to deduce parameter types differently, usually wrongly, and at leats in the case of DBD::mysql, different in every other release or so, and this can and does lead to data corruption, this module does type deduction itself.

What does it mean? Simple - sql parameters for placeholders will be explicitly marked as SQL_VARCHAR, SQL_INTEGER or SQL_DOUBLE the first time a statement is prepared.

To force a specific type, you can either continue to use e.g. sql casts, or you can make sure to consistently use strings or numbers. To make a perl scalar look enough like a string or a number, use this when passing it to sql_exec or a similar functions:

   "$string"   # to pass a string
   $num+0      # to pass a number

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 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).

$db = new <same arguments as connect_cached>

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

$db->dbh

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

$db->checked_dbh

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

$db->dsn

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

$db->login

Return the login name.

$db->password

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

SEE ALSO ^

PApp.

AUTHOR ^

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/
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