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
    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 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 "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.

  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.

  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 - 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.

