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README.md

DB::SQLite - SQLite access for Perl 6

Build Status

This is a reimplementation of Perl 6 bindings for SQLite.

Basic usage

my $s = DB::SQLite.new();  # You can pass in various connection options

Execute a query, and get a single value:

say $s.query('select 42').value;
# 42

Create a table:

$s.execute('create table foo (x int, y text)');

Insert some values using placeholders:

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

Or even fancy placeholders:

$s.query('insert into foo (x,y) values ($x,$y)', x => 2, y => 'that');

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

say $s.query('select * from foo where x = $x', :x(1)).array;
say $s.query('select * from foo where x = $x', :2x).hash;

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

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

Connection Information

When you create a DB::SQLite object, you can specify a filename option to .new for the database to open. If it isn't specified, it will default to an empty string which causes a private, temporary on-disk database to be created. This will be useless if you use more than one connection, since each will get its own database, but maybe you want that..

If you specify filename => ':memory' you will get a private, temporary, in-memory database. Again, this will not be shared across connections.

You can also use a busy-timeout option to specify in milliseconds, the amount of sleeping to wait for a locked table to become available. This defaults to 10000 (10 seconds). Setting to zero will turn off busy handling.

use DB::SQLite;

my $s = DB::SQLite.new(filename => 'this.db', busy-timeout => 50000);

DB::SQLite::Connection

The main DB::SQLite 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 $s.query('select * from foo').arrays;
my $db = $s.db;
.say for $db.query('select * from foo').arrays;
$db.finish;

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

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

Calling .prepare() on the DB::SQLite::Connection prepares and returns a DB::SQLite::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 = $s.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() under two conditions:

  1. You don't need placeholders/arguments.
  2. You don't want the results.

As a special added bonus you can execute multiple statements separated by semi-colons in one shot:

$s.execute(q:to/END/);
create table foo
(
   x int,
   y text
);
insert into foo (x,y) values (1, 'this');
insert into foo (x,y) values (2, 'that');
END

Transactions

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

my $db = $s.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.

Placeholders and Binding

SQLite parameters can take several different forms:

  • ?
  • ?NNN
  • :AAA
  • $AAA
  • @AAA

Where NNN is an integer value, and AAA is an identifier. When calling execute, the numbered binds are bound starting with 1 from the arguments to .execute (or .query):

my $sth = $s.db.prepare('select ?1, ?2, ?3');
say $sth.execute(1,2,3).array;
$sth.finish;

The named binds with $AAA placeholders are bound with named parameter pairs:

my $sth = $s.db.prepare('select $x, $y, $z');
say $sth.execute(:x(1), :y(2), :z(3)).array;
say $sth.execute(x => 1, y => 2, z => 3).array; # same thing
$sth.finish;

Binding the other placeholders is a little more complicated. They must be bound explicitly prior to calling .execute() (This will work with numbered placeholders too.):

my $sth = $s.db.prepare('select :x, $y, @z');
$sth.bind(':x', 1)
$sth.bind('$y', 2)
$sth.bind('@z', 3)
$sth.execute();
$sth.finish;

You don't have to bind every placeholder. If you leave one out, it just gets a NULL. If you .execute multiple times with the same statement, it will use whatever bindings are in place from previous executions. Since by default, statements get cached and re-used, the safest approach is always to bind every placeholder, even ones you want to be NULL. (Bind with an undefined type, such as Any for NULL).

You can even mix and match numbered and named placeholders if you want to (and are careful).

Results

Calling .query() on a DB::SQLite or DB::SQLite::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.

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:

Copyright © 2009-2016, the DBIish contributors All rights reserved.

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.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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