Alzabo::SQLMaker - Alzabo base class for RDBMS drivers

Alzabo documentation Contained in the Alzabo distribution.

Index

Code Index:

NAME

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Alzabo::SQLMaker - Alzabo base class for RDBMS drivers

SYNOPSIS

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  use Alzabo::SQLMaker::MySQL;

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

  # or better yet

  my $sql = $runtime_schema->sqlmaker;

DESCRIPTION

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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

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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()|"load" method.

load

Load the specified subclass.

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

Throws: Alzabo::Exception::Eval|Alzabo::Exceptions

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

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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()|"select (Alzabo::Table and/or Alzabo::Column objects)", insert()|"insert", update()|"update (Alzabo::Table)", and delete()|"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()|"from (Alzabo::Table object, ...)"

** function|"** function (Alzabo::Table object(s) and/or $string(s))"

insert

Followed by:

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

update (Alzabo::Table)

Followed by:

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

delete

Followed by:

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

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

** function|"** function (Alzabo::Table object(s) and/or $string(s))"

delete()|"delete"

Followed by:

where()|"where <see below">

order_by()|"order_by (Alzabo::Column objects)"

Throws: Alzabo::Exception::SQL|Alzabo::Exceptions

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

Followed by:

and()|"and (same as where)"

or()|"or (same as where)"

order_by()|"order_by (Alzabo::Column objects)"

Throws: Alzabo::Exception::SQL|Alzabo::Exceptions

and (same as where)

or (same as where)

These methods take the same parameters as the where()|"where <see below"> method.

Follows:

where()|"where <see below">

and()|"and (same as where)"

or()|"or (same as where)"

Followed by:

and()|"and (same as where)"

or()|"or (same as where)"

order_by()|"order_by (Alzabo::Column objects)"

Throws: Alzabo::Exception::SQL|Alzabo::Exceptions

order_by (Alzabo::Column objects)

Adds an ORDER BY clause to your SQL.

Follows:

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

where()|"where <see below">

and()|"and (same as where)"

or()|"or (same as where)"

Followed by:

limit()|"limit ($max, optional $offset)"

Throws: Alzabo::Exception::SQL|Alzabo::Exceptions

limit ($max, optional $offset)

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

Follows:

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

where()|"where <see below">

and()|"and (same as where)"

or()|"or (same as where)"

order_by()|"order_by (Alzabo::Column objects)"

Alzabo::Exception::SQL|Alzabo::Exceptions

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

Follows:

insert()|"insert"

Followed by:

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

Throws: Alzabo::Exception::SQL|Alzabo::Exceptions

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

Throws: Alzabo::Exception::SQL|Alzabo::Exceptions

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

This method'a parameter are exactly like those given to the values|values ( Alzabo::Column object => $value, ... ) method.

Follows:

update()|"update (Alzabo::Table)"

Followed by:

where()|"where <see below">

Throws: Alzabo::Exception::SQL|Alzabo::Exceptions

RETRIEVING SQL FROM THE OBJECT

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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

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To create a subclass of Alzabo::SQLMaker for your particular RDBMS requires only that the virtual methods|"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()|"_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

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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()|"limit ($max, optional $offset)" method was called. Some RDBMS's have special SQL syntax for LIMIT clauses. For those that don't support this, the Alzabo::Driver|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

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Dave Rolsky, <dave@urth.org>

Alzabo documentation Contained in the Alzabo distribution. 
package Alzabo::SQLMaker;

use strict;
use vars qw($VERSION $AUTOLOAD);

use Alzabo::Exceptions;
use Alzabo::Utils;

use Class::Factory::Util;
use Params::Validate qw( :all );
Params::Validate::validation_options( on_fail => sub { Alzabo::Exception::Params->throw( error => join '', @_ ) } );

$VERSION = 2.0;

1;

sub make_function
{
    my $class = caller;

    my %p =
	validate( @_,
		  { function => { type => SCALAR },
		    min => { type => SCALAR, optional => 1 },
		    max => { type => UNDEF | SCALAR, optional => 1 },
		    groups => { type => ARRAYREF },
		    quote => { type => ARRAYREF, optional => 1 },
		    format => { type => SCALAR, optional => 1 },
		    is_modifier => { type => SCALAR, default => 0 },
		    has_spaces => { type => SCALAR, default => 0 },
		    allows_alias => { type => SCALAR, default => 1 },
		    no_parens => { type => SCALAR, default => 0 },
		  } );

    my $valid = '';
    if ( $p{min} || $p{max} )
    {
	$valid .= 'validate_pos( @_, ';
	$valid .= join ', ', ('1') x $p{min};
    }

    if ( defined $p{min} && defined $p{max} && $p{max} > $p{min} )
    {
	$valid .= ', ';
	$valid .= join ', ', ('0') x ( $p{max} - $p{min} );
    }
    elsif ( exists $p{min} && ! defined $p{max} )
    {
	$valid .= ", ('1') x (\@_ - $p{min})";
    }
    $valid .= ' );' if $valid;

    my @args = "function => '$p{function}'";

    if ( ! defined $p{max} || $p{max} > 0 )
    {
	push @args, '                                      args => [@_]';
    }

    if ( $p{format} )
    {
	push @args, "                                      format => '$p{format}'";
    }

    if ( $p{quote} )
    {
	my $quote .= '                                     quote => [';
	$quote .= join ', ', @{ $p{quote} };
	$quote .= ']';
	push @args, $quote;
    }

    for my $k ( qw( is_modifier has_spaces allows_alias no_parens ) )
    {
        if ( $p{$k} )
        {
            push @args, "                                      $k => 1";
        }
    }

    my $args = join ",\n", @args;

    my $code = <<"EOF";
sub ${class}::$p{function}
{
    shift if defined \$_[0] && Alzabo::Utils::safe_isa( \$_[0], 'Alzabo::SQLMaker' );
    $valid
    return Alzabo::SQLMaker::Function->new( $args );
}
EOF

    eval $code;

    {
	no strict 'refs';
	push @{ "$class\::EXPORT_OK" }, $p{function};
	my $exp = \%{ "$class\::EXPORT_TAGS" };
	foreach ( @{ $p{groups} } )
	{
	    push @{ $exp->{$_}  }, $p{function};
	}
	push @{ $exp->{all} }, $p{function};
    }
}

sub load
{
    shift;
    my %p = @_;

    my $class = "Alzabo::SQLMaker::$p{rdbms}";
    eval "use $class";
    Alzabo::Exception::Eval->throw( error => $@ ) if $@;

    $class->init(@_);

    return $class;
}

sub available { __PACKAGE__->subclasses }

sub init
{
    1;
}

use constant NEW_SPEC => { driver => { isa => 'Alzabo::Driver' },
                           quote_identifiers  => { type => BOOLEAN,
                                                   default => 0 },
                         };

sub new
{
    my $class = shift;
    my %p = validate( @_, NEW_SPEC );

    return bless { last_op => undef,
		   expect => undef,
		   type => undef,
		   sql => '',
		   bind => [],
		   placeholders => [],
		   as_id => 'aaaaa10000',
                   alias_in_having => 1,
                   %p,
		 }, $class;
}

# this just needs to be some unique thing that won't ever look like a
# valid bound parameter
my $placeholder = do { my $x = 1; bless \$x, 'Alzabo::SQLMaker::Placeholder' };
sub placeholder { $placeholder }

sub last_op
{
    return shift->{last_op};
}

sub select
{
    my $self = shift;

    Alzabo::Exception::Params->throw( error => "The select method requires at least one parameter" )
	unless @_;

    $self->{sql} .= 'SELECT ';

    if ( lc $_[0] eq 'distinct' )
    {
	$self->{sql} .= ' DISTINCT ';
	shift;
    }

    my @sql;
    foreach my $elt (@_)
    {
	if ( Alzabo::Utils::safe_can( $elt, 'table' ) )
	{
            my $table = $elt->table;

	    $self->{column_tables}{"$table"} = 1;

            my $sql =
                ( $self->{quote_identifiers} ?
                  $self->{driver}->quote_identifier
                      ( $table->alias_name, $elt->name ) :
                  $table->alias_name . '.' . $elt->name );

            $sql .= ' AS ' .
                ( $self->{quote_identifiers} ?
                  $self->{driver}->quote_identifier( $elt->alias_name ) :
                  $elt->alias_name );

	    push @sql, $sql;
	}
	elsif ( Alzabo::Utils::safe_can( $elt, 'columns' ) )
	{
	    $self->{column_tables}{"$elt"} = 1;

            my @cols;

            foreach my $col ( $elt->columns )
            {
                my $sql =
                    ( $self->{quote_identifiers} ?
                      $self->{driver}->quote_identifier
                      ( $elt->alias_name, $col->name ) :
                      $elt->alias_name . '.' . $col->name );

                $sql .= ' AS ' .
                    ( $self->{quote_identifiers} ?
                      $self->{driver}->quote_identifier( $elt->alias_name ) :
                      $elt->alias_name );

                push @cols, $sql;
            }

	    push @sql, join ', ', @cols;
	}
	elsif ( Alzabo::Utils::safe_isa( $elt, 'Alzabo::SQLMaker::Function' ) )
	{
	    my $string = $elt->as_string( $self->{driver}, $self->{quote_identifiers} );

	    if ( $elt->allows_alias )
	    {
		push @sql, " $string AS " . $self->{as_id};
		$self->{functions}{$string} = $self->{as_id};
		++$self->{as_id};
	    }
	    else
	    {
		push @sql, $string;
	    }
	}
	elsif ( ! ref $elt )
	{
	    push @sql, $elt;
	}
	else
	{
	    Alzabo::Exception::SQL->throw
                    ( error => 'Arguments to select must be either column objects,' .
                               ' table objects, function objects, or plain scalars' );
	}
    }

    $self->{sql} .= join ', ', @sql;

    $self->{type} = 'select';
    $self->{last_op} = 'select';

    return $self;
}

sub from
{
    my $self = shift;

    $self->_assert_last_op( qw( select delete function ) );

    my $spec =
        $self->{last_op} eq 'select' ? { type => OBJECT | ARRAYREF } : { can => 'alias_name' };

    validate_pos( @_, ( $spec ) x @_ );

    $self->{sql} .= ' FROM ';

    if ( $self->{last_op} eq 'delete' )
    {
	$self->{sql} .=
	    join ', ', map { ( $self->{quote_identifiers} ?
                               $self->{driver}->quote_identifier( $_->name ) :
                               $_->name ) } @_;

	$self->{tables} = { map { $_ => 1 } @_ };
    }
    else
    {
        my $sql;

	$self->{tables} = {};

        my @plain;
	foreach my $elt (@_)
	{
	    if ( Alzabo::Utils::is_arrayref($elt) )
	    {
		$sql .= ' ' if $sql;

                $sql .= $self->_outer_join(@$elt);
	    }
            else
            {
                push @plain, $elt;
            }
        }

        foreach my $elt ( grep { ! exists $self->{tables}{$_ } } @plain )
        {
            $sql .= ', ' if $sql;

            if ( $self->{quote_identifiers} )
            {
                $sql .=
                    ( $self->{driver}->quote_identifier( $elt->name ) .
                      ' AS ' .
                      $self->{driver}->quote_identifier( $elt->alias_name ) );
            }
            else
            {
                $sql .= $elt->name . ' AS ' . $elt->alias_name;
            }

            $self->{tables}{$elt} = 1;
	}

        $self->{sql} .= $sql;
    }

    if ($self->{type} eq 'select')
    {
        foreach my $t ( keys %{ $self->{column_tables} } )
        {
	    unless ( $self->{tables}{$t} )
	    {
		my $err = 'Cannot select column ';
		$err .= 'unless its table is included in the FROM clause';
		Alzabo::Exception::SQL->throw( error => $err );
	    }
	}
    }

    $self->{last_op} = 'from';

    return $self;
}

use constant _OUTER_JOIN_SPEC => ( { type => SCALAR },
                                   ( { can => 'alias_name' } ) x 2,
                                   { type => UNDEF | ARRAYREF | OBJECT, optional => 1 },
                                   { type => UNDEF | ARRAYREF, optional => 1 },
                                 );

sub _outer_join
{
    my $self = shift;

    my $tables = @_ - 1;
    validate_pos( @_, _OUTER_JOIN_SPEC );

    my $type = uc shift;

    my $join_from = shift;
    my $join_on = shift;
    my $fk;
    $fk = shift if $_[0] && Alzabo::Utils::safe_isa( $_[0], 'Alzabo::ForeignKey' );
    my $where = shift;

    unless ($fk)
    {
	my @fk = $join_from->foreign_keys_by_table($join_on);

	Alzabo::Exception::Params->throw( error => "The " . $join_from->name . " table has no foreign keys to the " . $join_on->name . " table" )
	    unless @fk;

	Alzabo::Exception::Params->throw( error => "The " . $join_from->name . " table has more than 1 foreign key to the " . $join_on->name . " table" )
	    if @fk > 1;

	$fk = $fk[0];
    }

    my $sql;
    unless ( $self->{tables}{$join_from} )
    {
        $sql .=
            ( $self->{quote_identifiers} ?
              $self->{driver}->quote_identifier( $join_from->name ) :
              $join_from->name );

        $sql .= ' AS ';
        $sql .=
            ( $self->{quote_identifiers} ?
              $self->{driver}->quote_identifier( $join_from->alias_name ) :
              $join_from->alias_name );
    }

    $sql .= " $type OUTER JOIN ";

    $sql .= ( $self->{quote_identifiers} ?
              $self->{driver}->quote_identifier( $join_on->name ) :
              $join_on->name );

    $sql .= ' AS ';

    $sql .=
        ( $self->{quote_identifiers} ?
          $self->{driver}->quote_identifier( $join_on->alias_name ) :
          $join_on->alias_name );

    $sql .= ' ON ';

    if ( $self->{quote_identifiers} )
    {
        $sql .=
            ( join ' AND ',
              map { $self->{driver}->quote_identifier
                        ( $join_from->alias_name, $_->[0]->name ) .
                    ' = ' .
                    $self->{driver}->quote_identifier
                        ( $join_on->alias_name, $_->[1]->name )
                  } $fk->column_pairs );
    }
    else
    {
        $sql .=
            ( join ' AND ',
              map { $join_from->alias_name . '.' . $_->[0]->name .
                    ' = ' .
                    $join_on->alias_name . '.' .  $_->[1]->name
                  } $fk->column_pairs );
    }

    @{ $self->{tables} }{ $join_from, $join_on } = (1, 1);

    if ($where)
    {
        $sql .= ' AND ';

        # make a clone
        my $sql_maker = bless { %$self }, ref $self;
        $sql_maker->{sql} = '';
        # sharing same ref intentionally
        $sql_maker->{bind} = $self->{bind};
        $sql_maker->{tables} = $self->{tables};

        # lie to Alzabo::Runtime::process_where_clause
        $sql_maker->{last_op} = 'where';

        Alzabo::Runtime::process_where_clause( $sql_maker, $where );

        $sql .= $sql_maker->sql;

        $sql .= ' ';

        $self->{as_id} = $sql_maker->{as_id};
    }

    return $sql;
}

sub where
{
    my $self = shift;

    $self->_assert_last_op( qw( from set ) );

    $self->{sql} .= ' WHERE ';

    $self->{last_op} = 'where';

    $self->condition(@_) if @_;

    return $self;
}

sub having
{
    my $self = shift;

    $self->_assert_last_op( qw( group_by ) );

    $self->{sql} .= ' HAVING ';

    $self->{last_op} = 'having';

    $self->condition(@_) if @_;

    return $self;
}

sub and
{
    my $self = shift;

    $self->_assert_last_op( qw( subgroup_end condition ) );

    return $self->_and_or( 'and', @_ );
}

sub or
{
    my $self = shift;

    $self->_assert_last_op( qw( subgroup_end condition ) );

    return $self->_and_or( 'or', @_ );
}

sub _and_or
{
    my $self = shift;
    my $op = shift;

    $self->{sql} .= " \U$op ";

    $self->{last_op} = $op;

    $self->condition(@_) if @_;

    return $self;
}

sub subgroup_start
{
    my $self = shift;

    $self->_assert_last_op( qw( where having and or subgroup_start ) );

    $self->{sql} .= ' (';
    $self->{subgroup} ||= 0;
    $self->{subgroup}++;

    $self->{last_op} = 'subgroup_start';

    return $self;
}

sub subgroup_end
{
    my $self = shift;

    $self->_assert_last_op( qw( condition subgroup_end ) );

    Alzabo::Exception::SQL->throw( error => "Can't end a subgroup unless one has been started already" )
	unless $self->{subgroup};

    $self->{sql} .= ' )';
    $self->{subgroup}--;

    $self->{last_op} = $self->{subgroup} ? 'subgroup_end' : 'condition';

    return $self;
}

sub condition
{
    my $self = shift;

    validate_pos( @_,
		  { type => OBJECT },
		  { type => SCALAR },
		  { type => UNDEF | SCALAR | OBJECT },
		  ( { type => UNDEF | SCALAR | OBJECT, optional => 1 } ) x (@_ - 3) );

    my $lhs = shift;
    my $comp = uc shift;
    my $rhs = shift;

    my $in_having = $self->{last_op} eq 'having' ? 1 : 0;

    $self->{last_op} = 'condition';

    if ( $lhs->can('table') && $lhs->can('name') )
    {
	unless ( $self->{tables}{ $lhs->table } )
	{
	    my $err = 'Cannot use column (';
	    $err .= join '.', $lhs->table->name, $lhs->name;
	    $err .= ") in $self->{type} unless its table is included in the ";
	    $err .= $self->{type} eq 'update' ? 'UPDATE' : 'FROM';
	    $err .= ' clause';
	    Alzabo::Exception::SQL->throw( error => $err );
	}

	$self->{sql} .=
	    ( $self->{quote_identifiers} ?
              $self->{driver}->quote_identifier( $lhs->table->alias_name, $lhs->name ) :
              $lhs->table->alias_name . '.' . $lhs->name );
    }
    elsif ( $lhs->isa('Alzabo::SQLMaker::Function') )
    {
	my $string = $lhs->as_string( $self->{driver}, $self->{quote_identifiers} );

        if ( exists $self->{functions}{$string} &&
             ( ! $in_having || $self->{alias_in_having} ) )
        {
            $self->{sql} .= $self->{functions}{$string};
        }
        else
        {
            $self->{sql} .= $string;
        }
    }
    else
    {
        Alzabo::Exception::SQL->throw
            ( error => "Cannot use " . (ref $lhs) . " object as part of condition" );
    }

    if ( $comp eq 'BETWEEN' )
    {
	Alzabo::Exception::SQL->throw
	    ( error => "The BETWEEN comparison operator requires an additional argument" )
		unless @_ == 1;

	my $rhs2 = shift;

	Alzabo::Exception::SQL->throw
	    ( error => "The BETWEEN comparison operator cannot accept a subselect" )
		if grep { Alzabo::Utils::safe_isa( $_, 'Alzabo::SQLMaker' ) } $rhs, $rhs2;

	$self->{sql} .= ' BETWEEN ';
	$self->{sql} .= $self->_rhs($rhs);
	$self->{sql} .= " AND ";
	$self->{sql} .= $self->_rhs($rhs2);

	return;
    }

    if ( $comp eq 'IN' || $comp eq 'NOT IN' )
    {
	$self->{sql} .= " $comp (";

	$self->{sql} .=
	    join ', ', map { Alzabo::Utils::safe_isa( $_, 'Alzabo::SQLMaker' )
			     ?  '(' . $self->_subselect($_) . ')'
                             : $self->_rhs($_) } $rhs, @_;
	$self->{sql} .= ')';

	return;
    }

    Alzabo::Exception::Params->throw
	( error => 'Too many parameters to Alzabo::SQLMaker->condition method' )
	    if @_;

    if ( ! ref $rhs && defined $rhs )
    {
	$self->{sql} .= " $comp ";
	$self->{sql} .= $self->_rhs($rhs);
    }
    elsif ( ! defined $rhs )
    {
	if ( $comp eq '=' )
	{
	    $self->{sql} .= ' IS NULL';
	}
	elsif ( $comp eq '!=' || $comp eq '<>' )
	{
	    $self->{sql} .= ' IS NOT NULL';
	}
	else
	{
	    Alzabo::Exception::SQL->throw
		( error => "Cannot compare a column to a NULL with '$comp'" );
	}
    }
    elsif ( ref $rhs )
    {
	$self->{sql} .= " $comp ";
	if( $rhs->isa('Alzabo::SQLMaker') )
	{
	    $self->{sql} .= '(';
	    $self->{sql} .= $self->_subselect($rhs);
	    $self->{sql} .= ')';
	}
	else
	{
	    $self->{sql} .= $self->_rhs($rhs);
	}
    }
}

sub _rhs
{
    my $self = shift;
    my $rhs = shift;

    if ( Alzabo::Utils::safe_can( $rhs, 'table' ) )
    {
	unless ( $self->{tables}{ $rhs->table } )
	{
	    my $err = 'Cannot use column (';
	    $err .= join '.', $rhs->table->name, $rhs->name;
	    $err .= ") in $self->{type} unless its table is included in the ";
	    $err .= $self->{type} eq 'update' ? 'UPDATE' : 'FROM';
	    $err .= ' clause';
	    Alzabo::Exception::SQL->throw( error => $err );
	}

	return ( $self->{quote_identifiers} ?
                 $self->{driver}->quote_identifier( $rhs->table->alias_name, $rhs->name ) :
                 $rhs->table->alias_name . '.' . $rhs->name );
    }
    else
    {
	return $self->_bind_val($rhs);
    }
}

sub _subselect
{
    my $self = shift;
    my $sql = shift;

    push @{ $self->{bind} }, @{ $sql->bind };

    return $sql->sql;
}

sub order_by
{
    my $self = shift;

    $self->_assert_last_op( qw( select from condition group_by ) );

    Alzabo::Exception::SQL->throw
	( error => "Cannot use order by in a '$self->{type}' statement" )
	    unless $self->{type} eq 'select';

    validate_pos( @_, ( { type => SCALAR | OBJECT,
			  callbacks =>
			  { 'column_or_function_or_sort' =>
			    sub { Alzabo::Utils::safe_can( $_[0], 'table' ) ||
				  Alzabo::Utils::safe_isa( $_[0], 'Alzabo::SQLMaker::Function' ) ||
				  $_[0] =~ /^(?:ASC|DESC)$/i } } }
		      ) x @_ );

    $self->{sql} .= ' ORDER BY ';

    my $x = 0;
    my $last = '';
    foreach my $i (@_)
    {
	if ( Alzabo::Utils::safe_can( $i, 'table' ) )
	{
	    unless ( $self->{tables}{ $i->table } )
	    {
		my $err = 'Cannot use column (';
		$err .= join '.', $i->table->name, $i->name;
		$err .= ") in $self->{type} unless its table is included in the FROM clause";
		Alzabo::Exception::SQL->throw( error => $err );
	    }

	    # no comma needed for first column
	    $self->{sql} .= ', ', if $x++;
	    $self->{sql} .=
		( $self->{quote_identifiers} ?
                  $self->{driver}->quote_identifier( $i->table->alias_name, $i->alias_name ) :
                  $i->table->alias_name . '.' . $i->alias_name );

	    $last = 'column';
	}
	elsif ( Alzabo::Utils::safe_isa( $i, 'Alzabo::SQLMaker::Function' ) )
	{
	    my $string = $i->as_string( $self->{driver}, $self->{quote_identifiers} );
	    if ( exists $self->{functions}{$string} )
	    {
		$self->{sql} .= ', ', if $x++;
		$self->{sql} .= $self->{functions}{$string};
	    }
	    else
	    {
		$self->{sql} .= ', ', if $x++;
		$self->{sql} .= $string;
	    }

            $last = 'function';
	}
	else
	{
	    Alzabo::Exception::Params->throw
		( error => 'A sort specifier cannot follow another sort specifier in an ORDER BY clause' )
		    if $last eq 'sort';

	    $self->{sql} .= " \U$i";

	    $last = 'sort';
	}
    }

    $self->{last_op} = 'order_by';

    return $self;
}

sub group_by
{
    my $self = shift;

    $self->_assert_last_op( qw( select from condition ) );

    Alzabo::Exception::SQL->throw
	( error => "Cannot use group by in a '$self->{type}' statement" )
	    unless $self->{type} eq 'select';

    validate_pos( @_, ( { can => 'table' } ) x @_ );

    foreach my $c (@_)
    {
	unless ( $self->{tables}{ $c->table } )
	{
	    my $err = 'Cannot use column (';
	    $err .= join '.', $c->table->name, $c->name;
	    $err .= ") in $self->{type} unless its table is included in the FROM clause";
	    Alzabo::Exception::SQL->throw( error => $err );
	}
    }

    $self->{sql} .= ' GROUP BY ';
    $self->{sql} .=
	( join ', ',
	  map { ( $self->{quote_identifiers} ?
                  $self->{driver}->quote_identifier( $_->table->alias_name, $_->alias_name ) :
                  $_->table->alias_name . '.' . $_->alias_name ) }
	  @_ );

    $self->{last_op} = 'group_by';

    return $self;
}

sub insert
{
    my $self = shift;

    $self->{sql} .= 'INSERT ';

    $self->{type} = 'insert';
    $self->{last_op} = 'insert';

    return $self;
}

sub into
{
    my $self = shift;

    $self->_assert_last_op( qw( insert ) );

    validate_pos( @_, { can => 'alias_name' }, ( { can => 'table' } ) x (@_ - 1) );

    my $table = shift;
    $self->{tables} = { $table => 1 };

    foreach my $c (@_)
    {
	unless ( $c->table eq $table )
	{
	    my $err = 'Cannot into column (';
	    $err .= join '.', $c->table->name, $c->name;
	    $err .= ') because its table was not the one specified in the INTO clause';
	    Alzabo::Exception::SQL->throw( error => $err );
	}
    }

    $self->{columns} = [ @_ ? @_ : $table->columns ];

    $self->{sql} .= 'INTO ';

    $self->{sql} .= ( $self->{quote_identifiers} ?
                      $self->{driver}->quote_identifier( $table->name ) :
                      $table->name );

    $self->{sql} .= ' (';

    $self->{sql} .=
	( join ', ',
	  map { ( $self->{quote_identifiers} ?
                  $self->{driver}->quote_identifier( $_->name ) :
                  $_->name ) }
	  @{ $self->{columns} } );

    $self->{sql} .= ') ';

    $self->{last_op} = 'into';

    return $self;
}

sub values
{
    my $self = shift;

    $self->_assert_last_op( qw( into ) );

    validate_pos( @_, ( { type => UNDEF | SCALAR | OBJECT } ) x @_ );

    if ( ref $_[0] && $_[0]->isa('Alzabo::SQLMaker') )
    {
	$self->{sql} = $_[0]->sql;
	push @{ $self->{bind} }, $_[0]->bind;
    }
    else
    {
	my @vals = @_;

	Alzabo::Exception::Params->throw
	    ( error => "'values' method expects key/value pairs of column objects and values'" )
		if !@vals || @vals % 2;

	my %vals = map { ref $_ && $_->can('table') ? $_->name : $_ } @vals;
	foreach my $c ( @vals[ map { $_ * 2 } 0 .. int($#vals/2) ] )
	{
	    Alzabo::Exception::SQL->throw
		( error => $c->name . " column was not specified in the into method call" )
		    unless grep { $c eq $_ } @{ $self->{columns} };
	}

	foreach my $c ( @{ $self->{columns } } )
	{
	    Alzabo::Exception::SQL->throw
		( error => $c->name . " was specified in the into method call but no value was provided" )
		    unless exists $vals{ $c->name };
	}

	$self->{sql} .= 'VALUES (';
	$self->{sql} .=
            join ', ', ( map { $self->_bind_val_for_insert( $_, $vals{ $_->name } ) }
                         @{ $self->{columns} }
                       );
	$self->{sql} .= ')';
    }

    if ( @{ $self->{placeholders} } && @{ $self->{bind} } )
    {
        Alzabo::Exception::SQL->throw
	    ( error => "Cannot mix actual bound values and placeholders in call to values()" );
    }

    $self->{last_op} = 'values';

    return $self;
}

use constant UPDATE_SPEC => { can => 'alias_name' };

sub update
{
    my $self = shift;

    validate_pos( @_, UPDATE_SPEC );

    my $table = shift;

    $self->{sql} = 'UPDATE ';

    $self->{sql} .= ( $self->{quote_identifiers} ?
                      $self->{driver}->quote_identifier( $table->name ) :
                      $table->name );

    $self->{tables} = { $table => 1 };

    $self->{type} = 'update';
    $self->{last_op} = 'update';

    return $self;
}

sub set
{
    my $self = shift;
    my @vals = @_;

    $self->_assert_last_op('update');

    Alzabo::Exception::Params->throw
	( error => "'set' method expects key/value pairs of column objects and values'" )
	    if !@vals || @vals % 2;

    validate_pos( @_, ( { can => 'table' },
			{ type => UNDEF | SCALAR | OBJECT } ) x (@vals / 2) );

    $self->{sql} .= ' SET ';

    my @set;
    my $table = ( keys %{ $self->{tables} } )[0];
    while ( my ($col, $val) = splice @vals, 0, 2 )
    {
	unless ( $table eq $col->table )
	{
	    my $err = 'Cannot set column (';
	    $err .= join '.', $col->table->name, $col->name;
	    $err .= ') unless its table is included in the UPDATE clause';
	    Alzabo::Exception::SQL->throw( error => $err );
	}

	push @set,
	    ( $self->{quote_identifiers} ?
              $self->{driver}->quote_identifier( $col->name ) :
              $col->name ) .
            ' = ' . $self->_bind_val($val);
    }
    $self->{sql} .= join ', ', @set;

    $self->{last_op} = 'set';

    return $self;
}

sub delete
{
    my $self = shift;

    $self->{sql} .= 'DELETE ';

    $self->{type} = 'delete';
    $self->{last_op} = 'delete';

    return $self;
}

sub _assert_last_op
{
    my $self = shift;

    unless ( grep { $self->{last_op} eq $_ } @_ )
    {
	my $op = (caller(1))[3];
	$op =~ s/.*::(.*?)$/$1/;
	Alzabo::Exception::SQL->throw( error => "Cannot follow $self->{last_op} with $op" );
    }
}

use constant _BIND_VAL_FOR_INSERT_SPEC => ( { isa => 'Alzabo::Runtime::Column' },
                                            { type => UNDEF | SCALAR | OBJECT }
                                          );


sub _bind_val_for_insert
{
    my $self = shift;

    my ( $col, $val ) =
        validate_pos( @_, _BIND_VAL_FOR_INSERT_SPEC );

    if ( defined $val && $val eq $placeholder )
    {
        push @{ $self->{placeholders} }, $col->name;
        return '?';
    }
    else
    {
        return $self->_bind_val($val);
    }
}

use constant _BIND_VAL_SPEC => { type => UNDEF | SCALAR | OBJECT };

sub _bind_val
{
    my $self = shift;

    validate_pos( @_, _BIND_VAL_SPEC );

    return $_[0]->as_string( $self->{driver}, $self->{quote_identifiers} )
        if Alzabo::Utils::safe_isa( $_[0], 'Alzabo::SQLMaker::Function' );

    push @{ $self->{bind} }, $_[0];
    return '?';
}

sub sql
{
    my $self = shift;

    Alzabo::Exception::SQL->throw( error => "SQL contains unbalanced parentheses subgrouping: $self->{sql}" )
	if $self->{subgroup};

    return $self->{sql};
}

sub bind
{
    my $self = shift;
    return $self->{bind};
}

sub placeholders
{
    my $self = shift;

    my $x = 0;

    return map { $_ => $x++ } @{ $self->{placeholders} };
}

sub limit
{
    shift()->_virtual;
}

sub get_limit
{
    shift()->_virtual;
}

sub sqlmaker_id
{
    shift()->_virtual;
}

sub distinct_requires_order_by_in_select { 0 }

sub _virtual
{
    my $self = shift;

    my $sub = (caller(1))[3];
    $sub =~ s/.*::(.*?)$/$1/;
    Alzabo::Exception::VirtualMethod->throw( error =>
					     "$sub is a virtual method and must be subclassed in " . ref $self );
}

sub debug
{
    my $self = shift;
    my $fh = shift;

    print $fh '-' x 75 . "\n";
    print $fh "SQL\n - " . $self->sql . "\n";
    print $fh "Bound values\n";

    foreach my $b ( @{ $self->bind } )
    {
        my $out = $b;

        if ( defined $out )
        {
            if ( length $out > 75 )
            {
                $out = substr( $out, 0, 71 ) . ' ...';
            }
        }
        else
        {
            $out = 'NULL';
        }

        print $fh " - [$out]\n";
    }
}

package Alzabo::SQLMaker::Function;

use Params::Validate qw( :all );
Params::Validate::validation_options( on_fail => sub { Alzabo::Exception::Params->throw( error => join '', @_ ) } );

sub new
{
    my $class = shift;
    my %p = @_;

    $p{args} = [] unless defined $p{args};
    $p{quote} ||= [];

    return bless \%p, $class;
}

sub allows_alias { shift->{allows_alias} }

sub as_string
{
    my $self = shift;
    my $driver = shift;
    my $quote = shift;

    my @args;
    foreach ( 0..$#{ $self->{args} } )
    {
	if ( Alzabo::Utils::safe_can( $self->{args}[$_], 'table' ) )
	{
	    push @args,
		( $quote ?
                  $driver->quote_identifier( $self->{args}[$_]->table->alias_name,
                                             $self->{args}[$_]->name ) :
                  $self->{args}[$_]->table->alias_name . '.' .
                  $self->{args}[$_]->name );
	    next;
	}
	elsif ( Alzabo::Utils::safe_isa( $self->{args}[$_], 'Alzabo::SQLMaker::Function' ) )
	{
	    push @args, $self->{args}[$_]->as_string( $driver, $quote );
	    next;
	}

	# if there are more args than specified in the quote param
	# then this function must allow an unlimited number of
	# arguments, in which case the last value in the quote param
	# is the value that should be used for all of the extra
	# arguments.
	my $i = $_ > $#{ $self->{quote} } ? -1 : $_;
	push @args,
            $self->{quote}[$i] ? $driver->quote( $self->{args}[$_] ) : $self->{args}[$_];
    }

    my $sql = $self->{function};
    $sql =~ s/_/ /g if $self->{has_spaces};

    return $sql if $self->{is_modifier};

    $sql .= '('
        unless $self->{no_parens};

    if ( $self->{format} )
    {
	$sql .= sprintf( $self->{format}, @args );
    }
    else
    {
	$sql .= join ', ', @args;
    }

    $sql .= ')'
        unless $self->{no_parens};

    return $sql;
}

__END__