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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
Parameters
rdbms => $rdbms_name
The name of the RDBMS being used.
schema =>
Alzabo::Schemaobject
Returns
A new Alzabo::Driver object of the appropriate subclass.
Throws
tables
Returns
A list of strings containing the names of the tables in the database. See the DBI documentation of the DBI->tables method for more details.
Throws
handle ($optional_dbh)
Parameters
This method takes one optional parameter, a connected DBI handle. If this is given, then this handle is the new handle for the driver.
Returns
The active database handle.
Throws
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.
Parameters (for all methods below)
sql => $sql_string
bind => $bind_value or \@bind_values
limit => [ $max, optional $offset ] (optional)
$offsetdefaults to 0.This parameters has no effect for the methods that return only one row. For the others, it causes the drivers to skip
$offsetrows and then return only$maxrows. This is useful if the RDBMS being used does not supportLIMITclauses.
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
statement
Parameters
limit => [ $max, optional $offset ] (optional)
$offset defaults to 0.
Returns
A new Alzabo::DriverStatement handle, ready to return data via the Alzabo::DriverStatement->next or Alzabo::DriverStatement->next_as_hash methods.
Throws
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
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
all_rows
Returns
If the select for which this statement is cursor was for a single column (or aggregate value), then 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
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
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
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
A 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 the 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.
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.
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 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.
AUTHOR
Dave Rolsky, <dave@urth.org>