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 <see below>

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>