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NAME

Alzabo::Driver - Alzabo base class for RDBMS drivers

SYNOPSIS

  use Alzabo::Driver;

  my $driver = Alzabo::Driver->new( rdbms => 'MySQL',
                                    schema => $schema );

DESCRIPTION

This is the base class for all Alzabo::Driver modules. To instantiate a driver call this class's new() method. See SUBCLASSING Alzabo::Driver for information on how to make a driver for the RDBMS of your choice.

This class throws several, exceptions, one of which, Alzabo::Exception::Driver, has additional methods not present in other exception classes. See Alzabo::Exception::Driver METHODS for a description of these methods.

METHODS

available

Returns a list of names representing the available Alzabo::Driver subclasses. Any one of these names would be appropriate as the "rdbms" parameter for the Alzabo::Driver->new method.

new

The constructor takes the following parameters:

• rdbms => $rdbms_name

  The name of the RDBMS being used.

• schema => Alzabo::Schema object

It returns a new Alzabo::Driver object of the appropriate subclass.

Throws: Alzabo::Exception::Eval

tables

Returns a list of strings containing the names of the tables in the database. See the DBI documentation of the DBI->tables method for more details.

Throws: Alzabo::Exception::Driver

handle ($optional_dbh)

This method takes one optional parameter, a connected DBI handle. If this is given, then this handle is the new handle for the driver.

It returns the active database handle.

Throws: Alzabo::Exception::Params

Data Retrieval methods

Some of these methods return lists of data (the rows, rows_hashref, and column methods). With large result sets, this can use a lot memory as these lists are created in memory before being returned to the caller. To avoid this, it may be desirable to use the functionality provided by the Alzabo::DriverStatement class, which allows you to fetch results one row at a time.

These methods all accept the following parameters:

• sql => $sql_string
• bind => $bind_value or \@bind_values
• limit => [ $max, optional $offset ] (optional)

  The $offset defaults to 0.

  This parameter has no effect for the methods that return only one row. For the others, it causes the drivers to skip $offset rows and then return only $max rows. This is useful if the RDBMS being used does not support LIMIT clauses.

rows

Returns an array of array references containing the data requested.

rows_hashref

Returns an array of hash references containing the data requested. The hash reference keys are the columns being selected. All the key names are in uppercase.

one_row

Returns an array or scalar containing the data returned, depending on context.

one_row_hash

Returns a hash containing the data requested. The hash keys are the columns being selected. All the key names are in uppercase.

column

Returns an array containing the values for the first column of each row returned.

do

Use this for non-SELECT SQL statements.

Returns the number of rows affected.

Throws: Alzabo::Exception::Driver

statement

This methods returns a new Alzabo::DriverStatement handle, ready to return data via the Alzabo::DriverStatement->next() or Alzabo::DriverStatement->next_as_hash() methods.

Throws: Alzabo::Exception::Driver

rdbms_version

Returns the version string of the database backend currently in use. The form of this string will vary depending on which driver subclass is being used.

quote (@strings)

This methods calls the underlying DBI handles quote() method on the array of strings provided, and returns the quoted versions.

quote_identifier (@strings)

This methods calls the underlying DBI handles quote_identifier() method on the array of strings provided, and returns the quoted versions.

Alzabo::DriverStatement

This class is a wrapper around DBI's statement handles. It finishes automatically as appropriate so the end user does need not worry about doing this.

next

Use this method in a while loop to fetch all the data from a statement.

Returns an array containing the next row of data for statement or an empty list if no more data is available.

Throws: Alzabo::Exception::Driver

next_as_hash

For backwards compatibility, this is also available as next_hash().

Returns a hash containing the next row of data for statement or an empty list if no more data is available. All the keys of the hash will be lowercased.

Throws: Alzabo::Exception::Driver

all_rows

If the select for which this statement is cursor was for a single column (or aggregate value), then this method returns an array containing each remaining value from the database.

Otherwise, it returns an array of array references, each one containing a returned row from the database.

Throws: Alzabo::Exception::Driver

all_rows_hash

Returns an array of hashes, each hash representing a single row returned from the database. The hash keys are all in lowercase.

Throws: Alzabo::Exception::Driver

execute (@bind_values)

Executes the associated statement handle with the given bound parameters. If the statement handle is still active (it was previously executed and has more data left) then its finish() method will be called first.

Throws: Alzabo::Exception::Driver

count

Returns the number of rows returned so far.

Alzabo::Exception::Driver METHODS

In addition to the methods inherited from Exception::Class::Base, objects in this class also contain several methods specific to this subclass.

sql

Returns the SQL statement in use at the time the error occurred, if any.

bind

Returns an array reference contaning the bound parameters for the SQL statement, if any.

SUBCLASSING Alzabo::Driver

To create a subclass of Alzabo::Driver for your particular RDBMS is fairly simple. First of all, there must be a DBD::* driver for it, as Alzabo::Driver is built on top of DBI.

Here's a sample header to the module using a fictional RDBMS called FooDB:

 package Alzabo::Driver::FooDB;

 use strict;
 use vars qw($VERSION);

 use Alzabo::Driver;

 use DBI;
 use DBD::FooDB;

 use base qw(Alzabo::Driver);

The next step is to implement a new method and the methods listed under Virtual Methods. The new method should look a bit like this:

 1:  sub new
 2:  {
 3:      my $proto = shift;
 4:      my $class = ref $proto || $proto;
 5:      my %p = @_;
 6:
 7:      my $self = bless {}, $class;
 8:
 9:      return $self;
 10:  }

The hash %p contains any values passed to the Alzabo::Driver->new method by its caller.

Lines 1-7 should probably be copied verbatim into your own new method. Line 5 can be deleted if you don't need to look at the parameters.

Look at the included Alzabo::Driver subclasses for examples. Feel free to contact me for further help if you get stuck. Please tell me what database you're attempting to implement, what its DBD::* driver is, and include the code you've written so far.

Virtual Methods

The following methods are not implemented in Alzabo::Driver itself and must be implemented in a subclass.

Parameters for connect(), create_database(), and drop_database()

• user => $db_username
• password => $db_pw
• host => $hostname
• port => $port

All of these default to undef. See the appropriate DBD driver documentation for more details.

After the driver is created, it will have access to its associated schema object in $self->{schema}.

connect

Some drivers may accept or require more arguments than specified above.

Note that Alzabo::Driver subclasses are not expected to cache connections. If you want to do this please use Apache::DBI under mod_perl or don't call connect() more than once per process.

create_database

Attempts to create a new database for the schema attached to the driver. Some drivers may accept or require more arguments than specified above.

drop_database

Attempts to drop the database for the schema attached to the driver.

schemas

Returns a list of schemas in the specified RDBMS. This method may accept some or all of the parameters which can be given to connect().

supports_referential_integrity

Should return a boolean value indicating whether or not the RDBMS supports referential integrity constraints.

next_sequence_number (Alzabo::Column object)

This method is expected to return the value of the next sequence number based on a column object. For some databases (MySQL, for example), the appropriate value is undef. This is accounted for in the Alzabo code that calls this method.

begin_work

Notify Alzabo that you wish to start a transaction.

rollback

Rolls back the current transaction.

commit

Notify Alzabo that you wish to finish a transaction. This is basically the equivalent of calling commit.

get_last_id

Returns the last primary key id created via a sequenced column.

rdbms_version

Returns the version of the server to which the driver is connected.

driver_id

Returns the driver's name. This should be something that can be passed to Alzabo::Driver->new() as a "name" parameter.

AUTHOR

Dave Rolsky, <dave@urth.org>

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