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.
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>