ORLite(3) User Contributed Perl Documentation ORLite(3)NAMEORLite - Extremely light weight SQLite-specific ORM
SYNOPSIS
package Foo;
# Simplest possible usage
use strict;
use ORLite 'data/sqlite.db';
my @awesome = Foo::Person->select(
'where first_name = ?',
'Adam',
);
package Bar;
# All available options enabled or specified.
# Some options shown are mutually exclusive,
# this code would not actually run.
use ORLite {
package => 'My::ORM',
file => 'data/sqlite.db',
user_version => 12,
readonly => 1,
create => sub {
my $dbh = shift;
$dbh->do('CREATE TABLE foo ( bar TEXT NOT NULL )');
},
tables => [ 'table1', 'table2' ],
cleanup => 'VACUUM',
prune => 1,
};
DESCRIPTION
SQLite is a light single file SQL database that provides an excellent
platform for embedded storage of structured data.
However, while it is superficially similar to a regular server-side SQL
database, SQLite has some significant attributes that make using it
like a traditional database difficult.
For example, SQLite is extremely fast to connect to compared to server
databases (1000 connections per second is not unknown) and is
particularly bad at concurrency, as it can only lock transactions at a
database-wide level.
This role as a superfast internal data store can clash with the roles
and designs of traditional object-relational modules like Class::DBI or
DBIx::Class.
What this situation would seem to need is an object-relation system
that is designed specifically for SQLite and is aligned with its
idiosyncracies.
ORLite is an object-relation system specifically tailored for SQLite
that follows many of the same principles as the ::Tiny series of
modules and has a design and feature set that aligns directly to the
capabilities of SQLite.
Further documentation will be available at a later time, but the
synopsis gives a pretty good idea of how it works.
How ORLite Works
In short, ORLite discovers the schema of a SQLite database, and then
uses code generation to build a set of packages for talking to that
database.
In the simplest form, your target root package "uses" ORLite, which
will do the schema discovery and code generation at compile-time.
When called, ORLite generates two types of package.
Firstly, it builds database connectivity, transaction support, and
other purely database level functionality into your root namespace.
Then it will create one sub-package underneath the root package for
each table contained in the database.
OPTIONSORLite takes a set of options for the class construction at compile
time as a HASH parameter to the "use" line.
As a convenience, you can pass just the name of an existing SQLite file
to load, and ORLite will apply defaults to all other options.
# The following are equivalent
use ORLite $filename;
use ORLite {
file => $filename,
};
The behaviour of each of the options is as follows:
package
The optional "package" parameter is used to provide the Perl root
namespace to generate the code for. This class does not need to exist
as a module on disk, nor does it need to have anything loaded or in the
namespace.
By default, the package used is the package that is calling ORLite's
import method (typically via the "use ORLite { ... }" line).
file
The compulsory "file" parameter (the only compulsory parameter)
provides the path to the SQLite file to use for the ORM class tree.
If the file already exists, it must be a valid SQLite file match that
supported by the version of DBD::SQLite that is installed on your
system.
ORLite will throw an exception if the file does not exist, unless you
also provide the "create" option to signal that ORLite should create a
new SQLite file on demand.
If the "create" option is provided, the path provided must be
creatable. When creating the database, ORLite will also create any
missing directories as needed.
user_version
When working with ORLite, the biggest risk to the stability of your
code is often the reliability of the SQLite schema structure over time.
When the database schema changes the code generated by ORLite will also
change. This can easily result in an unexpected change in the API of
your class tree, breaking the code that sits on top of those generated
APIs.
To resolve this, ORLite supports a feature called schema version-
locking.
Via the "user_version" SQLite pragma, you can set a revision for your
database schema, increasing the number each time to make a non-trivial
chance to your schema.
SQLite> PRAGMA user_version = 7
When creating your ORLite package, you should specificy this schema
version number via the "user_version" option.
use ORLite {
file => $filename,
user_version => 7,
};
When connecting to the SQLite database, the "user_version" you provide
will be checked against the version in the schema. If the versions do
not match, then the schema has unexpectedly changed, and the code that
is generated by ORLite would be different to the expected API.
Rather than risk potentially destructive errors caused by the changing
code, ORLite will simply refuse to run and throw an exception.
Thus, using the "user_version" feature allows you to write code against
a SQLite database with high-certainty that it will continue to work. Or
at the very least, that should the SQLite schema change in the future
your code fill fail quickly and safely instead of running away and
causing unknown behaviour.
By default, the "user_version" option is false and the value of the
SQLite "PRAGMA user_version" will not be checked.
readonly
To conserve memory and reduce complexity, ORLite will generate the API
differently based on the writability of the SQLite database.
Features like transaction support and methods that result in "INSERT",
"UPDATE" and "DELETE" queries will only be added if they can actually
be run, resulting in an immediate "no such method" exception at the
Perl level instead of letting the application do more work only to hit
an inevitable SQLite error.
By default, the "reaodnly" option is based on the filesystem
permissions of the SQLite database (which matches SQLite's own
writability behaviour).
However the "readonly" option can be explicitly provided if you wish.
Generally you would do this if you are working with a read-write
database, but you only plan to read from it.
Forcing "readonly" to true will halve the size of the code that is
generated to produce your ORM, reducing the size of any auto-generated
API documentation using ORLite::Pod by a similar amount.
It also ensures that this process will only take shared read locks on
the database (preventing the chance of creating a dead-lock on the
SQLite database).
create
The "create" option is used to expand ORLite beyond just consuming
other people's databases to produce and operating on databases user the
direct control of your code.
The "create" option supports two alternative forms.
If "create" is set to a simple true value, an empty SQLite file will be
created if the location provided in the "file" option does not exist.
If "create" is set to a "CODE" reference, this function will be
executed on the new database before ORLite attempts to scan the schema.
The "CODE" reference will be passed a plain DBI connection handle,
which you should operate on normally. Note that because "create" is
fired before the code generation phase, none of the functionality
produced by the generated classes is available during the execution of
the "create" code.
The use of "create" option is incompatible with the "readonly" option.
tables
The "tables" option should be a reference to an array containing a list
of table names. For large or complex SQLite databases where you only
need to make use of a fraction of the schema limiting the set of tables
will reduce both the startup time needed to scan the structure of the
SQLite schema, and reduce the memory cost of the class tree.
If the "tables" option is not provided, ORLite will attempt to produce
a class for every table in the main schema that is not prefixed with
with "sqlite_".
cache
use ORLite {
file => 'dbi:SQLite:sqlite.db',
user_version => 2,
cache => 'cache/directory',
};
The "cache" option is used to reduce the time needed to scan the SQLite
database table structures and generate the code for them, by saving the
generated code to a cache directory and loading from that file instead
of generating it each time from scratch.
cleanup
When working with embedded SQLite databases containing rapidly changing
state data, it is important for database performance and general health
to make sure you VACUUM or ANALYZE the database regularly.
The "cleanup" option should be a single literal SQL statement.
If provided, this statement will be automatically run on the database
during "END"-time, after the last transaction has been completed.
This will typically either by a full 'VACUUM ANALYZE' or the more
simple 'VACUUM'.
prune
In some situation, such as during test scripts, an application will
only need the created SQLite database temporarily. In these situations,
the "prune" option can be provided to instruct ORLite to delete the
SQLite database when the program ends.
If any directories were made in order to create the SQLite file, these
directories will be cleaned up and removed as well.
If "prune" is enabled, you should generally not use "cleanup" as any
cleanup operation will be made pointless when "prune" deletes the file.
By default, the "prune" option is set to false.
shim
In some situtations you may wish to make extensive changes to the
behaviour of the classes and methods generated by ORLite. Under normal
circumstances all code is generated into the table class directly,
which can make overriding method difficult.
The "shim" option will make ORLite generate all of it's methods into a
seperate "Foo::TableName::Shim" class, and leave the main table class
"Foo::TableName" as a transparent subclass of the shim.
This allows you to alter the behaviour of a table class without having
to do nasty tricks with symbol tables in order to alter or replace
methods.
package My::Person;
# Write a log message when we create a new object
sub create {
my $class = shift;
my $self = SUPER::create(@_);
my $name = $self->name;
print LOG "Created new person '$name'\n";
return $self;
}
The "shim" option is global. It will alter the structure of all table
classes at once. However, unless you are making alterations to a class
the impact of this different class structure should be zero.
ROOT PACKAGE METHODS
All ORLite root packages receive an identical set of methods for
controlling connections to the database, transactions, and the issueing
of queries of various types to the database.
The example root package Foo::Bar is used in any examples.
All methods are static, ORLite does not allow the creation of a
Foo::Bar object (although you may wish to add this capability
yourself).
dsn
my $string = Foo::Bar->dsn;
The "dsn" accessor returns the dbi connection string used to connect to
the SQLite database as a string.
dbh
my $handle = Foo::Bar->dbh;
To reliably prevent potential SQLite deadlocks resulting from multiple
connections in a single process, each ORLite package will only ever
maintain a single connection to the database.
During a transaction, this will be the same (cached) database handle.
Although in most situations you should not need a direct DBI connection
handle, the "dbh" method provides a method for getting a direct
connection in a way that is compatible with ORLite's connection
management.
Please note that these connections should be short-lived, you should
never hold onto a connection beyond the immediate scope.
The transaction system in ORLite is specifically designed so that code
using the database should never have to know whether or not it is in a
transation.
Because of this, you should never call the ->disconnect method on the
database handles yourself, as the handle may be that of a currently
running transaction.
Further, you should do your own transaction management on a handle
provided by the <dbh> method.
In cases where there are extreme needs, and you absolutely have to
violate these connection handling rules, you should create your own
completely manual DBI->connect call to the database, using the connect
string provided by the "dsn" method.
The "dbh" method returns a DBI::db object, or throws an exception on
error.
connect
my $dbh = Foo::Bar->connect;
The "connect" method is provided for the (extremely rare) situation in
which you need a raw connection to the database, evading the normal
tracking and management provided of the ORM.
The use of raw connections in this manner is strongly discouraged, as
you can create fatal deadlocks in SQLite if either the core ORM or the
raw connection uses a transaction at any time.
To summarise, do not use this method unless you REALLY know what you
are doing.
YOU HAVE BEEN WARNED!
connected
my $active = Foo::Bar->connected;
The "connected" method provides introspection of the connection status
of the library. It returns true if there is any connection or
transaction open to the database, or false otherwise.
begin
Foo::Bar->begin;
The "begin" method indicates the start of a transaction.
In the same way that ORLite allows only a single connection, likewise
it allows only a single application-wide transaction.
No indication is given as to whether you are currently in a transaction
or not, all code should be written neutrally so that it works either
way or doesn't need to care.
Returns true or throws an exception on error.
While transaction support is always built for every ORLite-generated
class tree, if the database is opened "readonly" the "commit" method
will not exist at all in the API, and your only way of ending the
transaction (and the resulting persistent connection) will be
"rollback".
commit
Foo::Bar->commit;
The "commit" method commits the current transaction. If called outside
of a current transaction, it is accepted and treated as a null
operation.
Once the commit has been completed, the database connection falls back
into auto-commit state. If you wish to immediately start another
transaction, you will need to issue a separate ->begin call.
Returns true or throws an exception on error.
commit_begin
Foo::Bar->begin;
# Code for the first transaction...
Foo::Bar->commit_begin;
# Code for the last transaction...
Foo::Bar->commit;
By default, ORLite-generated code uses opportunistic connections.
Every <select> you call results in a fresh DBI "connect", and a
"disconnect" occurs after query processing and before the data is
returned. Connections are only held open indefinitely during a
transaction, with an immediate "disconnect" after your "commit".
This makes ORLite very easy to use in an ad-hoc manner, but can have
performance implications.
While SQLite itself can handle 1000 connections per second, the
repeated destruction and repopulation of SQLite's data page caches
between your statements (or between transactions) can slow things down
dramatically.
The "commit_begin" method is used to "commit" the current transaction
and immediately start a new transaction, without disconnecting from the
database.
Its exception behaviour and return value is identical to that of a
plain "commit" call.
rollback
The "rollback" method rolls back the current transaction. If called
outside of a current transaction, it is accepted and treated as a null
operation.
Once the rollback has been completed, the database connection falls
back into auto-commit state. If you wish to immediately start another
transaction, you will need to issue a separate ->begin call.
If a transaction exists at END-time as the process exits, it will be
automatically rolled back.
Returns true or throws an exception on error.
rollback_begin
Foo::Bar->begin;
# Code for the first transaction...
Foo::Bar->rollback_begin;
# Code for the last transaction...
Foo::Bar->commit;
By default, ORLite-generated code uses opportunistic connections.
Every <select> you call results in a fresh DBI "connect", and a
"disconnect" occurs after query processing and before the data is
returned. Connections are only held open indefinitely during a
transaction, with an immediate "disconnect" after your "commit".
This makes ORLite very easy to use in an ad-hoc manner, but can have
performance implications.
While SQLite itself can handle 1000 connections per second, the
repeated destruction and repopulation of SQLite's data page caches
between your statements (or between transactions) can slow things down
dramatically.
The "rollback_begin" method is used to "rollback" the current
transaction and immediately start a new transaction, without
disconnecting from the database.
Its exception behaviour and return value is identical to that of a
plain "commit" call.
do
Foo::Bar->do(
'insert into table (foo, bar) values (?, ?)',
{},
$foo_value,
$bar_value,
);
The "do" method is a direct wrapper around the equivalent DBI method,
but applied to the appropriate locally-provided connection or
transaction.
It takes the same parameters and has the same return values and error
behaviour.
selectall_arrayref
The "selectall_arrayref" method is a direct wrapper around the
equivalent DBI method, but applied to the appropriate locally-provided
connection or transaction.
It takes the same parameters and has the same return values and error
behaviour.
selectall_hashref
The "selectall_hashref" method is a direct wrapper around the
equivalent DBI method, but applied to the appropriate locally-provided
connection or transaction.
It takes the same parameters and has the same return values and error
behaviour.
selectcol_arrayref
The "selectcol_arrayref" method is a direct wrapper around the
equivalent DBI method, but applied to the appropriate locally-provided
connection or transaction.
It takes the same parameters and has the same return values and error
behaviour.
selectrow_array
The "selectrow_array" method is a direct wrapper around the equivalent
DBI method, but applied to the appropriate locally-provided connection
or transaction.
It takes the same parameters and has the same return values and error
behaviour.
selectrow_arrayref
The "selectrow_arrayref" method is a direct wrapper around the
equivalent DBI method, but applied to the appropriate locally-provided
connection or transaction.
It takes the same parameters and has the same return values and error
behaviour.
selectrow_hashref
The "selectrow_hashref" method is a direct wrapper around the
equivalent DBI method, but applied to the appropriate locally-provided
connection or transaction.
It takes the same parameters and has the same return values and error
behaviour.
prepare
The "prepare" method is a direct wrapper around the equivalent DBI
method, but applied to the appropriate locally-provided connection or
transaction
It takes the same parameters and has the same return values and error
behaviour.
In general though, you should try to avoid the use of your own prepared
statements if possible, although this is only a recommendation and by
no means prohibited.
pragma
# Get the user_version for the schema
my $version = Foo::Bar->pragma('user_version');
The "pragma" method provides a convenient method for fetching a pragma
for a datase. See the SQLite documentation for more details.
TABLE PACKAGE METHODS
When you use ORLite, your database tables will be available as objects
named in a camel-cased fashion. So, if your model name is Foo::Bar...
use ORLite {
package => 'Foo::Bar',
file => 'data/sqlite.db',
};
... then a table named 'user' would be accessed as "Foo::Bar::User",
while a table named 'user_data' would become "Foo::Bar::UserData".
base
my $namespace = Foo::Bar::User->base; # Returns 'Foo::Bar'
Normally you will only need to work directly with a table class, and
only with one ORLite package.
However, if for some reason you need to work with multiple ORLite
packages at the same time without hardcoding the root namespace all the
time, you can determine the root namespace from an object or table
class with the "base" method.
table
print Foo::Bar::UserData->table; # 'user_data'
While you should not need the name of table for any simple operations,
from time to time you may need it programatically. If you do need it,
you can use the "table" method to get the table name.
table_info
# List the columns in the underlying table
my $columns = Foo::Bar::User->table_info;
foreach my $c ( @$columns ) {
print "Column $c->{name} $c->{type}";
print " not null" if $c->{notnull};
print " default $c->{dflt_value}" if defined $c->{dflt_value};
print " primary key" if $c->{pk};
print "\n";
}
The "table_info" method is a wrapper around the SQLite "table_info"
pragma, and provides simplified access to the column metadata for the
underlying table should you need it for some advanced function that
needs direct access to the column list.
Returns a reference to an "ARRAY" containing a list of columns, where
each column is a reference to a "HASH" with the keys "cid",
"dflt_value", "name", "notnull", "pk" and "type".
new
my $user = Foo::Bar::User->new(
name => 'Your Name',
age => 23,
);
The "new" constructor creates an anonymous object, without reading it
from or writing it to the database. It also won't do validation of any
kind, since ORLite is designed for use with embedded databases and
presumes that you know what you are doing.
insert
my $user = Foo::Bar::User->new(
name => 'Your Name',
age => 23,
)->insert;
The "insert" method takes an existing anonymous object and inserts it
into the database, returning the object as a convenience.
It provides the second half of the slower manual two-phase object
construction process.
If the table has an auto-incrementing primary key (and you have not
provided a value for it yourself) the identifier for the new record
will be fetched back from the database and set in your object.
my $object = Foo::Bar::User->new( name => 'Foo' )->insert;
print "Created new user with id " . $user->id . "\n";
create
my $user = Foo::Bar::User->create(
name => 'Your Name',
age => 23,
);
While the "new" + "insert" methods are useful when you need to do
interesting constructor mechanisms, for most situations you already
have all the attributes ready and just want to create and insert the
record in a single step.
The "create" method provides this shorthand mechanism and is just the
functional equivalent of the following.
sub create {
shift->new(@_)->insert;
}
It returns the newly created object after it has been inserted.
load
my $user = Foo::Bar::User->load( $id );
If your table has single column primary key, a "load" method will be
generated in the class. If there is no primary key, the method is not
created.
The "load" method provides a shortcut mechanism for fetching a single
object based on the value of the primary key. However it should only be
used for cases where your code trusts the record to already exists.
It returns a "Foo::Bar::User" object, or throws an exception if the
object does not exist.
select
my @users = Foo::Bar::User->select;
my $users = Foo::Bar::User->select( 'where name = ?', @args );
The "select" method is used to retrieve objects from the database.
In list context, returns an array with all matching elements. In
scalar context an array reference is returned with that same data.
You can filter the results or order them by passing SQL code to the
method.
my @users = DB::User->select( 'where name = ?', $name );
my $users = DB::User->select( 'order by name' );
Because "select" provides only the thinnest of layers around pure SQL
(it merely generates the "SELECT ... FROM table_name") you are free to
use anything you wish in your query, including subselects and function
calls.
If called without any arguments, it will return all rows of the table
in the natural sort order of SQLite.
iterate
Foo::Bar::User->iterate( sub {
print $_->name . "\n";
} );
The "iterate" method enables the processing of large tables one record
at a time without loading having to them all into memory in advance.
This plays well to the strength of SQLite, allowing it to do the work
of loading arbitrarily large stream of records from disk while
retaining the full power of Perl when processing the records.
The last argument to "iterate" must be a subroutine reference that will
be called for each element in the list, with the object provided in the
topic variable $_.
This makes the "iterate" code fragment above functionally equivalent to
the following, except with an O(1) memory cost instead of O(n).
foreach ( Foo::Bar::User->select ) {
print $_->name . "\n";
}
You can filter the list via SQL in the same way you can with "select".
Foo::Bar::User->iterate(
'order by ?', 'name',
sub {
print $_->name . "\n";
}
);
You can also use it in raw form from the root namespace for better
control. Using this form also allows for the use of arbitrarily
complex queries, including joins. Instead of being objects, rows are
provided as ARRAY references when used in this form.
Foo::Bar->iterate(
'select name from user order by name',
sub {
print $_->[0] . "\n";
}
);
count
my $everyone = Foo::Bar::User->count;
my $young = Foo::Bar::User->count( 'where age <= ?', 13 );
You can count the total number of elements in a table by calling the
"count" method with no arguments. You can also narrow your count by
passing sql conditions to the method in the same manner as with the
"select" method.
delete
# Delete a single object from the database
$user->delete;
# Delete a range of rows from the database
Foo::Bar::User->delete( 'where age <= ?', 13 );
The "delete" method comes in two variations, depending on whether you
call it on a single object or an entire class.
When called as an instance methods "delete" will delete the single row
representing that object, based on the primary key of that object.
The object that you delete will be left intact and untouched, and you
remain free to do with it whatever you wish.
When called as a static method on the class name "delete" allows the
deletion of a range of zero or more records from that table.
It takes the same parameters for deleting as the "select" method, with
the exception that you MUST provide a condition parameter and can NOT
use a conditionless "delete" call to clear out the entire table. This
is done to limit accidental deletion.
truncate
# Clear out all records from the table
Foo::Bar::User->truncate;
The "truncate" method takes no parameters and is used for only one
purpose, to completely empty a table of all rows.
Having a separate method from "delete" not only prevents accidents, but
will also do the deletion via the direct SQLite "TRUNCATE TABLE" query.
This uses a different deletion mechanism, and is significantly faster
than a plain SQL "DELETE".
TO DO
- Support for intuiting reverse relations from foreign keys
- Document the 'create' and 'table' params
SUPPORT
Bugs should be reported via the CPAN bug tracker at
<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=ORLite>
For other issues, contact the author.
AUTHOR
Adam Kennedy <adamk@cpan.org>
SEE ALSO
ORLite::Mirror, ORLite::Migrate, ORLite::Pod
COPYRIGHT
Copyright 2008 - 2011 Adam Kennedy.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
The full text of the license can be found in the LICENSE file included
with this module.
perl v5.14.1 2011-06-07 ORLite(3)
