NAME¶
ORLite - 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¶
ORLite discovers the schema of a SQLite database, and then generates the code
for a complete set of classes that let you work with the objects stored in
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 packages.
Firstly, it builds database connectivity, transaction support, and other purely
database level functionality into your root namespace.
Secondly, it will create one sub-package underneath the namespace of the root
module for each table or view it finds in the database.
Once the basic table support has been generated, it will also try to load an
"overlay" module of the same name. Thus, by created a Foo::TableName
module on disk containing "extra" code, you can extend the original
and add additional functionality to it.
OPTIONS¶
ORLite 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 "readonly" 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
separate "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.
unicode¶
You can use this option to tell ORLite that your database uses unicode.
At the moment, it just enables the "sqlite_unicode" option while
connecting to your database. There'll be more in the future.
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.
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 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 back 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.
The "id" accessor is a convenience method that is added to your table
class to increase the readability of your code when ORLite detects certain
patterns of column naming.
For example, take the following definition where convention is that all primary
keys are the table name followed by "_id".
create table foo_bar (
foo_bar_id integer not null primary key,
name string not null,
)
When ORLite detects the use of this pattern, and as long as the table does not
have an "id" column, the additional "id" accessor will be
added to your class, making these expressions equivalent both in function and
performance.
my $foo_bar = My::FooBar->create( name => 'Hello' );
# Column name accessor
$foo_bar->foo_bar_id;
# Convenience id accessor
$foo_bar->id;
As you can see, the latter involves much less repetition and reads much more
cleanly.
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 will delete the single row representing an object,
based on the primary key or SQLite rowid 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.
delete_where¶
# Delete a range of rows from the database
Foo::Bar::User->delete( 'age <= ?', 13 );
The "delete_where" static method allows the delete of large numbers of
rows from a database while protecting against accidentally doing a boundless
delete (the "truncate" method is provided specifically for this
purpose).
It takes the same parameters for deleting as the "select" method, with
the exception that the "where" keyword is automatically provided for
your and should not be passed in.
This ensures that providing an empty of null condition results in an invalid SQL
query and the deletion will not occur.
Returns the number of rows deleted from the database (which may be zero).
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 - 2012 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.