DB::MySQL - MySQL access for Perl 6

This is a reimplementation of Perl 6 bindings for MySQL.

Basic usage

use DB::MySQL;
my $mysql = DB::MySQL.new();  # You can pass in various options

Execute a query, and get a single value:

say $mysql.execute('select 42').value;
# 42

Create a table:

$mysql.execute('create table foo (x int, y varchar(80))');

Insert some values using placeholders:

$mysql.query('insert into foo (x,y) values (?,?)', 1, 'this');

Execute a query returning a row as an array or hash;

say $mysql.query('select * from foo where x = ?', 1).array;
say $mysql.query('select * from foo where x = ?', 1).hash;

Execute a query returning a bunch of rows as arrays or hashes:

.say for $mysql.query('select * from foo').arrays;
.say for $mysql.query('select * from foo').hashes;

.query() caches a prepared statement, and can have placeholders and arguments - .execute() does not prepare/cache and can't have placeholders. Both can return results.

Installation

This module relies on libmysqlclient.so. For Ubuntu, I install this with:

sudo apt install libmysqlclient-dev

I worked with version 5.7 of the API. It may or may not work with other versions. You can see the client version with:

perl6 -MDB::MySQL::Native -e 'say mysql_get_client_info'

There are likely 64-bit Linux dependencies in the code. Patches welcome if someone wants to make it on other OSes.

Connection Information

There are many options that can be specified to DB::MySQL.new():

:host - defaults to localhost
:port - defaults to 3306
:user
:password
:socket
:database - optional, sets current database
:connect-timeout - timeout in seconds for a connect attempt.
:read-timeout - timeout in seconds for each attempt to read from the servers.
:write-timeout - timeout in seconds for each attempt to write to the server.
:default-file - Read options from the named file instead of my.cnf.
:group - defaults to 'client'. Reads options from the specified group in the .my.cnf file. Undefine this to ignore defaults file.

The easiest way to connect is to put your options in .my.cnf.

DB::MySQL::Connection

The main DB::MySQL object acts as a factory for connections, maintaining a cache of connections already created. A new connection can be requested with the .db method, but often this isn't needed. When you are finished with a connection, you can explicitly return it to the cache with .finish.

You can call .query() or .execute() on the main DB::SQLite object, but all they really do is allocate a DB::SQLite::Connection (either from the cache, or create a new one) and call those methods on it, then return the connection to the cache.

These are equivalent:

.say for $mysql.query('select * from foo').arrays;

my $db = $mysql.db;
.say for $mysql.query('select * from foo').arrays;
$db.finish;

The connection object also has some extra methods for separately preparing and executing the query:

my $db = $mysql.db;
my $sth = $db.prepare('insert into foo (x,y) values (?,?)');
$sth.execute(1, 'this');
$sth.execute(2, 'that');
$db.finish;

You can also call .finish() on the statement:

my $sth = $mysql.db.prepare('insert into foo (x,y) values (?,?)');
$sth.execute(1, 'this');
$sth.execute(2, 'that');
$sth.finish;

The statement will finish the associated connection, returning it to the cache. Yet another way to do it is to pass :finish in to the execute.

my $sth = $mysql.db.prepare('insert into foo (x,y) values (?,?)');
$sth.execute(1, 'this');
$sth.execute(2, 'that', :finish);

And finally, a cool Perl 6ish way is the will trait to install a Phaser directly on the variable:

{
    my $sth will leave { .finish } = $mysql.db.prepare('insert into foo (x,y) values (?,?)');
    $sth.execute(1, 'this');
    $sth.execute(2, 'that');
}

Calling .prepare() on the DB::MySQL::Connection prepares and returns a DB::MySQL::Statement that can then be .execute()ed. The prepared statement is also retained in a cache with the connection. If the same statement is prepared again on the same connection, the cached object will be returned instead of re-preparing. If you don't want it to be cached, you can pass in the :nocache option.

my $sth = $mysql.db.prepare('insert into foo (x,y) values (?,?)', :nocache);
$sth.execute(1, 'this');
$sth.execute(2, 'that', :finish);

You must still take care to call .finish() to return the connection to the connection cache so it will get reused. (Or take care NOT to call .finish() if you don't want the connection to be reused, possibly in another thread.)

For the main object, or the connection object, .execute() is used instead of .query() if you don't need placeholders/arguments.

Transactions

The database connection object can also manage transactions with the .begin, .commit, and .rollback methods:

my $db = $mysql.db;
my $sth = $db.prepare('insert into foo (x,y) values (?,?)');
$db.begin;
$sth.execute(1, 'this');
$sth.execute(2, 'that');
$db.commit;
$db.finish;

The begin/commit ensure that the statements between them happen atomically, either all or none.

Transactions can also dramatically improve performance for some actions, such as performing thousands of inserts/deletes/updates since the indexes for the affected table can be updated in bulk once for the entire transaction.

If you .finish the database prior to a .commit, an uncommitted transaction will automatically be rolled back.

As a convenience, .commit also returns the database object, so you can just $db.commit.finish.

Results

Calling .query() on a DB::MySQL or DB::MySQL::Connection, or calling .execute() on a DB::SQLite::Statement with an SQL SELECT or something that returns data, a DB::SQLite::Result object will be returned.

The query results can be consumed from that object with the following methods:

.value - a single scalar result
.array - a single array of results from one row
.hash - a single hash of results from one row
.arrays - a sequence of arrays of results from all rows
.hashes - a sequence of hashes of results from all rows

If the query isn't a select or otherwise doesn't return data, such as an INSERT, UPDATE, or DELETE, it will return the number of rows affected.

By default, the entire result of the query is retrieved immediately from the server to the client. You can pass in the :nostore option to .query or .execute to avoid this behavior. It will then retrieve the results from the server as you consume them on the client. This will hold up server resources while you retrieve the results, so exercise care with this.

Exceptions

All database errors, including broken SQL queries, are thrown as exceptions.

Acknowledgements

Inspiration taken from the existing Perl6 DBIish module as well as the Perl 5 Mojo::Pg from the Mojolicious project.

License

Portions thanks to DBIish:

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

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