NAME

Ima::DBI - Database connection caching and organization

SYNOPSIS


            
              
              # Class-wide methods.
__PACKAGE__->set_db($db_name, $data_source, $user, $password);
__PACKAGE__->set_db($db_name, $data_source, $user, $password, \%attr);
__PACKAGE__->set_sql($sql_name, $statement, $db_name);
# Object methods.
$dbh = $obj->db_*;      # Where * is the name of the db connection.
$sth = $obj->sql_*;     # Where * is the name of the sql statement.
$rc = $obj->commit;             #UNIMPLEMENTED
$rc = $obj->commit(@db_names);  #UNIMPLEMENTED
$rc = $obj->rollback;            #UNIMPLEMENTED
$rc = $obj->rollback(@db_names); #UNIMPLEMENTED
$obj->clear_db_cache;            #UNIMPLEMENTED
$obj->clear_db_cache(@db_names); #UNIMPLEMENTED
$obj->clear_sql_cache;             #UNIMPLMENTED
$obj->clear_sql_cache(@sql_names); #UNIMPLMENTED
$obj->DBIwarn;
$dbh->clear_cache;  #UNIMPLEMENTED
# Modified statement handle methods.
$rv = $sth->execute;
$rv = $sth->execute(@bind_values);
$rv = $sth->execute(\@bind_values, \@bind_cols);
$row_ref = $sth->fetch;
@row     = $sth->fetch;
$row_ref = $sth->fetch_hash;
%row     = $sth->fetch_hash;
$rows_ref = $sth->fetchall;
@rows     = $sth->fetchall;
$rows_ref = $sth->fetchall_hash;
@tbl      = $sth->fetchall_hash;
$sth->clear_cache;  #UNIMPLEMENTED

DESCRIPTION

Ima::DBI attempts to organize and facilitate caching and more efficient use of database connections and statement handles.

One of the things I always found annoying about writing large programs with DBI was making sure that I didn't have duplicate database handles open. I was also annoyed by the somewhat wasteful nature of the prepare/execute/finish route I'd tend to go through in my subroutines. The new DBI->connect_cached and DBI->prepare_cached helped alot, but I still had to throw around global datasource, username and password information.

So, after a while I grew a small library of DBI helper routines and techniques. Ima::DBI is the culmination of all this, put into a nice(?), clean(?) class to be inherited from.

Why should I use this thing?

Ima::DBI is a little odd, and it's kinda hard to explain. So lemme explain why you'd want to use this thing...

Consolidation of all SQL statements and database information

No matter what, embedding one language into another is messy. DBI alleviates this somewhat, but I've found a tendency to have that scatter the SQL around inside the Perl code. Ima::DBI allows you to easily group the SQL statements in one place where they are easier to maintain (especially if one developer is writing the SQL, another writing the Perl). Alternatively, you can place your SQL statement alongside the code which uses it. Whatever floats your boat.

Database connection information (data source, username, password, atrributes, etc...) can also be consolidated together and tracked.

Both the SQL and the connection info are probably going to change alot, so having them well organized and easy to find in the code is a Big Help.
Holds off opening a database connection until necessary.

While Ima::DBI is informed of all your database connections and SQL statements at compile-time, it will not connect to the database until you actually prepare a statement on that connection.

This is obviously very good for programs that sometimes never touch the database. It's also good for code that has lots of possible connections and statements, but which typically only use a few. Kinda like an autoloader.
Easy integration of the DBI handles into your class

Ima::DBI causes each database handle to be associated with your class, allowing you to pull handles from an instance of your object, as well as making many oft-used DBI methods available directly from your instance.

This gives you a cleaner OO design, since you can now just throw around the object as usual and it will carry its associated DBI baggage with it.

Honors taint mode * INCOMPLETE *

It always struck me as a design deficiency that tainted SQL statements could be passed to $sth->prepare(). For example:


            
              
              # $user is from an untrusted source and is tainted.
$user = get_user_data_from_the_outside_world;
$sth = $dbh->prepare('DELETE FROM Users WHERE User = $user');

Looks innocent enough... but what if $user was the string "1 OR User LIKE %". You just blew away all your users, hope you have backups.

Using taint mode can prevent this problem, but DBI does not honor taint since all of its system calls are done inside XS code. So, Ima::DBI manually checks to see if a given SQL statement is tainted before passing it on to prepare.

Taints returned data * INCOMPLETE *

Databases should be like any other system call. Its the scary Outside World, thus it should be tainted. Simp.
Encapsulation of some of the more repetative bits of everyday DBI usage

I get lazy alot and I forget to do things I really should, like using bind_cols(), or rigorous error checking. Ima::DBI does some of this stuff automatic, other times it just makes it more convenient.
Encapsulation of DBI's cache system

DBI's automatic handle caching system is relatively new, some people aren't aware of its use. Ima::DBI uses it automatically, so you don't have to worry your pretty little head about it.
Sharing of database and sql information amongst inherited classes

Any SQL and connections created by a class is available to its children via normal method inheritance.
Convenience and orthoganality amongst statement handle methods

It always struck me odd that DBI didn't take much advantage of Perl's context sensitivity. Ima::DBI redefines some of the various fetch methods to fix this oversight; it also adds a few new methods for convenience.
Guarantees one connection per program.

One program, one database connection (per database user). One program, one prepared statement handle (per statement, per database user). That's what Ima::DBI enforces. Extremely handy in persistant environments (servers, daemons, mod_perl, FastCGI, etc...)
Encourages use of bind parameters and columns

Bind parameters are safer and more efficient than embedding the column information straight into the SQL statement. Bind columns are more efficient than normal fetching. Ima::DBI pretty much requires the usage of the former, and eases the use of the latter.

Why shouldn't I use this thing.

It's all about OO

Although it is possible to use Ima::DBI as a stand-alone module as part of a function-oriented design, its generally not to be used unless integrated into an object-oriented design.
Overkill for small programs
Overkill for programs with only one or two SQL statements
Overkill for programs that only use their SQL statements once

Ima::DBI's caching will probably prove to be an unecessary performance hog if you never use the same SQL statement twice.

USAGE

The basic steps to "DBIing" a class are:

Inherit from Ima::DBI
Set up and name all your database connections via set_db()
Set up and name all your SQL statements via set_sql()
Use sql_* to retrieive your statement handles as needed.

Have a look at the EXAMPLE below.

TAINTING

Ima::DBI, unlike DBI, honors taint mode.

For the time being it will be a sweeping thing, no Ima::DBI or Ima::DBI::st method will accept tainted data. This may be relaxed in the future.

In addition, Ima::DBI taints all data returned from the database.

This feature is incomplete, as I have yet to wrap all applicable DBI methods.

METHODS

Class methods

set_db


            
              
              __PACKAGE__->set_db($db_name, $data_source, $user, $password);
__PACKAGE__->set_db($db_name, $data_source, $user, $password, \%attr);

This method is used in place of DBI->connect to create your database handles.

Sets up a new DBI database handle associated to $db_name. All other arguments are passed through to DBI->connect_cached (See TODO below).

A new method is created for each db you setup. This new method is db_$db_name... so, for example, __PACKAGE__->set_db("foo", ...) will create a method called db_foo().

If no %attr is supplied (RaiseError => 1, AutoCommit => 0, PrintError => 0) is assumed. This is a better default IMHO.

The actual database handle creation (and thus the database connection) is held off until a prepare is attempted with this handle.

set_sql


            
              
              __PACKAGE__->set_sql($sql_name, $statement, $db_name);

This method is used in place of DBI->prepare to create your statement handles.

Sets up a new statement handle using associated to $sql_name using the database connection associated with $db_name. $statement is passed through to DBI->prepare_cached to create the statement handle.

A new method is created for each statement you set up. This new method is sql_$sql_name... so, as with set_db, __PACKAGE__->set_sql("bar", ..., "foo"); will create a method called sql_bar() which uses the database connection from db_foo().

The actual statement handle creation is held off until sql_* is first called on this name.

Object methods

db_*


            
              
              $dbh = $obj->db_*;

This is how you directly access a database handle you set up with set_db.

The actual particular method name is derived from what you told set_db.

db_* will handle all the issues of making sure you're already connected to the database.

sql_*


            
              
              $sth = $obj->sql_*;

This is how you access a statement handle set up with set_sql.

sql_* will handle all the issues of making sure the database is already connected, and the statement handle is prepared.

clear_db_cache *UNIMPLEMENTED*


            
              
              $obj->clear_db_cache;
$obj->clear_db_cache(@db_names);

Ima::DBI uses the DBI->connect_cached to cache open database handles. For whatever reason you might want to clear this cache out and start over again.

A call to clear_db_cache with no arguments deletes all database handles out of the cache and all associated statement handles. Otherwise it only deletes those handles listed in @db_names (and their associated statement handles).

Note that clearing from the cache does not necessarily destroy the database handle. Something else might have a reference to it.

Alternatively, you may do: $obj->db_Name->clear_cache;

clear_sql_cache *UNIMPLEMENTED*


            
              
              $obj->clear_sql_cache;
$obj->clear_sql_cache(@sql_names);

Does the same thing as clear_db_cache, except it does it in relation to statement handles.

Alternatively, you may do: $obj->sql_Name->clear_cache;

DBIwarn *UNIMPLEMENTED*


            
              
              $obj->DBIwarn;

Prints a warning relative to the last sql_ or db_ used showing the name, statement (or data source and user), DBI->errstr and line number. Something resembling:


            
              
              warn sprintf "%s had a problem while executing %s:  %s at line %d",
    $name, $sql, $sth->errstr, $line;

Useful for quickie things like:


            
              
              # If we can't delete this user, throw a warning.
$obj->sql_DeleteUser->execute($uid) || $obj->DBIwarn;

Modified database handle methods

Ima::DBI makes some of the methods available to your object that are normally only available via the database handle. In addition, it spices up the API a bit.

commit *UNIMPLEMENTED*


            
              
              $rc = $obj->commit;
$rc = $obj->commit(@db_names);

Derived from $dbh->commit() and basically does the same thing.

If called with no arguments, it causes commit() to be called on all database handles associated with $obj. Otherwise it commits all database handles whose names are listed in @db_names.

Alternatively, you may like to do: $rc = $obj->db_Name->commit;

rollback *UNIMPLEMENTED*


            
              
              $rc = $obj->rollback;
$rc = $obj->rollback(@db_names);

Derived from $dbj->rollback, it acts just like Ima::DBI->commit, except that it calls rollback().

Alternatively, you may like to do: $rc = $obj->db_Name->rollback;

clear_cache *UNIMPLEMENTED*


            
              
              $dbh->clear_cache;

Provides a mechanism to clear a given database handle from the cache.

Modified statement handle methods

Ima::DBI overrides the normal DBI statement handle with its own, slightly modified, version. Don't worry, it inherits from DBI::st, so anything not explicitly mentioned here will work just like in normal DBI.

execute


            
              
              $rv = $sth->execute;
$rv = $sth->execute(@bind_values);
$rv = $sth->execute(\@bind_values, \@bind_cols);

DBI::st->execute is overridden to enhance execute() a bit.

If called with no arguments, or with a simple list, execute() operates normally. When when called with two array references, it performs the functions of bind_param, execute and bind_columns similar to the following:


            
              
              $sth->execute(@bind_values);
$sth->bind_columns(undef, @bind_cols);

Thus a typical idiom would be:


            
              
              $sth->execute([$this, $that], [\($foo, $bar)]);

Of course, this method provides no way of passing bind attributes through to bind_param or bind_columns. If that is necessary, then you must perform the bind_param, execute, bind_col sequence yourself.

clear_cache *UNIMPLEMENTED*


            
              
              $sth->clear_cache;

Provides a mechanism to clear a given statement handle from the cache.

fetching

The following are modifications or expansions on DBI's various fetch methods. Most are simply context sensitive implementations. Some just have shorter names.

Remember that most of the list context versions of the fetch methods tend to use more memory and be slower. Same with the fetchall methods. Use with care.

fetch


            
              
              $row_ref = $sth->fetch;
@row     = $sth->fetch;

A context sensitive version of fetch(). When in scalar context, it will act as fetchrow_arrayref. In list context it will use fetchrow_array.

fetch_hash


            
              
              $row_ref = $sth->fetch_hash;
%row     = $sth->fetch_hash;

A modification on fetchrow_hashref. When in scalar context, it acts just as fetchrow_hashref() does. In list context it returns the complete hash.

fetchall


            
              
              $rows_ref = $sth->fetchall;
@rows     = $sth->fetchall;

A modification on fetchall_arrayref. In scalar context it acts as fetchall_arrayref. In list it returns an array of references to rows fetched.

fetchall_hashref


            
              
              $rows_ref = $sth->fetchall_hash;
@rows     = $sth->fetchall_hash;

A mating of fetchall_arrayref() with fetchrow_hashref(). It gets all rows from the hash, each as hash references. In scalar context it returns a reference to an array of hash references. In list context it returns a list of hash references.

EXAMPLE


            
              
              package Foo;
use base qw(Ima::DBI);
# Set up database connections (but don't connect yet)
__PACKAGE__->set_db('Users', 'dbi:Oracle:Foo', 'admin', 'passwd');
__PACKAGE__->set_db('Customers', 'dbi:Oracle:Foo', 'Staff', 'passwd');
# Set up SQL statements to be used through out the program.
__PACKAGE__->set_sql('FindUser', <<"SQL", 'Users');
    SELECT  *
    FROM    Users
    WHERE   Name LIKE ?
SQL
__PACKAGE__->set_sql('ChangeLanguage', <<"SQL", 'Customers');
    UPDATE  Customers
    SET     Language = ?
    WHERE   Country = ?
SQL
# rest of the class as usual.
package main:
$obj = Foo->new;
eval {
    # Does connect & prepare
    my $sth = $obj->sql_FindUser;
    # bind_params, execute & bind_columns
    $sth->execute(['Likmi%'], [\($name)]);
    while( $sth->fetch ) {
        print $name;
    }
     
    # Uses cached database and statement handles
    $sth = $obj->sql_FindUser;
    # bind_params & execute.
    $sth->execute('%Hock');
    @names = $sth->fetchall;
     
    # connects, prepares
    $rows_altered = $obj->sql_ChangeLanguage->execute(qw(es_MX mx));
};
unless ($@) {
    # Everything went okay, commit the changes to the customers.
    $obj->commit('Customers');
}
else {
    $obj->rollback('Customers');
    warn "DBI failure:  $@";    
}

TODO, Caveat, etc....

Unstable Interface: I haven't totally decided if I'm satisfied with the way this module works, so expect the worst, the interface will change.
DBI->connect_cached undocumented: Ima::DBI uses DBI->connect_cached, an undocumented feature in DBI, to handle its cache to connections, just like prepare_cached does. Eventually this feature will mature, but right now (as of DBI 1.06) its a little risky.
execute() extensions questionable: I'm not really sure the additional functionality added to execute() is all that useful.
tainting may be too broad: Having Ima::DBI not accept any tainted data at all is probably too general, but I'd rather be too strict to start than be too lax and try to restrict later. In the future, certain methods may accept tainted data.
Manual tainting incomplete: My method of spreading disease through the returned data does not appear to reach referenced data properly.
sql_* and db_* should take arguments: But what? Pass through to execute and then return the $sth?
I seriously doubt its thread safe.: You can bet cupcackes to sno-cones that much havoc will be rought if Ima::DBI is used in a threaded Perl.
Should make use of private_* handle method to store information
Having difficulty storing a list of dbh and sth names.: Storing the association between names and handles is fine, via the closures (and thus, the symbol table), but trying to store a complete list of all names available to a given object (and thus, inheritable) is difficult. Many minor methods are unimplemented until I figure out this problem.

AUTHOR

Michael G Schwern <schwern@pobox.com>

THANKS TO


            
              
              Tim Bunce, for enduring all my DBI questions.
Arena Networks, for effectively paying for me to write this module.

	Global
`s`	Focus search bar
`?`	Bring up this help dialog

	GitHub
`g` `p`	Go to pull requests
`g` `i`	go to github issues (only if github is preferred repository)

	POD
`g` `a`	Go to author
`g` `c`	Go to changes
`g` `i`	Go to issues
`g` `d`	Go to dist
`g` `r`	Go to repository/SCM
`g` `s`	Go to source
`g` `b`	Go to file browse

	Search terms
module: (e.g. module:Plugin)
distribution: (e.g. distribution:Dancer auth)
author: (e.g. author:SONGMU Redis)
version: (e.g. version:1.00)