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NAME

Alzabo::SQLMaker - Alzabo base class for RDBMS drivers

SYNOPSIS

  use Alzabo::SQLMaker::MySQL;

  my $sql = Alzabo::SQLMaker::MySQL->new( driver => $driver_object );

  # or better yet

  my $sql = $runtime_schema->sqlmaker;

DESCRIPTION

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

METHODS

available

Returns A list of names representing the available Alzabo::SQLMaker subclasses. Any one of these names would be appropriate as a parameter for the Alzabo::SQLMaker->load() method.

load

Load the specified subclass.

This takes one parameter, the name of the RDBMS being used.

Throws: Alzabo::Exception::Eval

new

This takes two parameters:

• driver

  The driver object being used by the schema.

• quote_identifiers

  A boolean value indicating whether or not identifiers should be quoted. This defaults to false.

GENERATING SQL

This class can be used to generate SQL by calling methods that are the same as those used in SQL (select(), update(), etc.) in sequence, with the appropriate parameters.

There are four entry point methods, select(), insert(), update(), and delete(). Attempting to call any other method without first calling one of these is an error.

Entry Points

These methods are called as class methods and return a new object.

select (Alzabo::Table and/or Alzabo::Column objects)

This begins a select. The columns to be selected are the column(s) passed in, and/or the columns of the table(s) passed in as arguments.

Followed by:

from()

** function

insert

Followed by:

into()

update (Alzabo::Table)

Followed by:

set()

delete

Followed by:

from()

Other Methods

All of these methods return the object itself, making it possible to chain together method calls such as:

 Alzabo::SQLMaker->select($column)->from($table)->where($other_column, '>', 2);

from (Alzabo::Table object, ...)

The table(s) from which we are selecting data.

Follows:

select()

** function

delete()

Followed by:

where()">

order_by()

Throws: Alzabo::Exception::SQL

where

The first parameter to where must be an Alzabo::Column object or SQL function. The second is a comparison operator of some sort, given as a string. The third argument can be an Alzabo::Column object, a value (a number or string), or an Alzabo::SQLMaker object. The latter is treated as a subselect.

Values given as parameters will be properly quoted and escaped.

Some comparison operators allow additional parameters.

The BETWEEN comparison operator requires a fourth argument. This must be either an Alzabo::Column object or a value.

The IN and <NOT IN> operators allow any number of additional parameters, which may be Alzabo::Column objects, values, or Alzabo::SQLMaker objects.

Follows:

from()

Followed by:

and()

or()

order_by()

Throws: Alzabo::Exception::SQL

and (same as where)

or (same as where)

These methods take the same parameters as the where()"> method.

Follows:

where()">

and()

or()

Followed by:

and()

or()

order_by()

Throws: Alzabo::Exception::SQL

order_by (Alzabo::Column objects)

Adds an ORDER BY clause to your SQL.

Follows:

from()

where()">

and()

or()

Followed by:

limit()

Throws: Alzabo::Exception::SQL

limit ($max, optional $offset)

Specifies a limit on the number of rows to be returned. The offset parameter is optional.

Follows:

from()

where()">

and()

or()

order_by()

Alzabo::Exception::SQL

into (Alzabo::Table object, optional Alzabo::Column objects)

Used to specify what table an insert is into. If column objects are given then it is expected that values will only be given for that object. Otherwise, it assumed that all columns will be specified in the values() method.

Follows:

insert()

Followed by:

values()

Throws: Alzabo::Exception::SQL

values (Alzabo::Column object => $value, ...)

This method expects to recive an structured like a hash where the keys are Alzabo::Column objects and the values are the value to be inserted into that column.

Follows:

into()

Throws: Alzabo::Exception::SQL

set (Alzabo::Column object => $value, ...)

This method'a parameter are exactly like those given to the values method.

Follows:

update()

Followed by:

where()">

Throws: Alzabo::Exception::SQL

RETRIEVING SQL FROM THE OBJECT

sql

This method can be called at any time, though obviously it will not return valid SQL unless called at a natural end point. In the future, an exception may be thrown if called when the SQL is not in a valid state.

Returns the SQL generated so far as a string.

bind

Returns an array reference containing the parameters to be bound to the SQL statement.

SUBCLASSING Alzabo::SQLMaker

To create a subclass of Alzabo::SQLMaker for your particular RDBMS requires only that the virtual methods listed below be implemented.

In addition, you may choose to override any of the other methods described in this documentation. For example, the MySQL subclass override the _subselect() method because MySQL cannot support sub-selects.

Subclasses are also expected to offer for export various sets of functions matching SQL functions. See the Alzabo::SQLMaker::MySQL subclass implementation for details.

VIRTUAL METHODS

The following methods must be implemented by the subclass:

limit

See above for the definition of this method.

get_limit

This method may return undef even if the limit() method was called. Some RDBMS's have special SQL syntax for LIMIT clauses. For those that don't support this, the Alzabo::Driver module takes a "limit" parameter.

The return value of this method can be passed in as that parameter.

If the RDBMS does not support LIMIT clauses, the return value is an array reference containing two values, the maximum number of rows allowed and the row offset (the first row that should be used).

If the RDBMS does support LIMIT clauses, then the return value is undef.

sqlmaker_id

Returns the subclass's name. This should be something that can be passed to Alzabo::SQLMaker->load() as a parameter.

AUTHOR

Dave Rolsky, <dave@urth.org>

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