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 / 
SQL-Builder-0.03
/ SQL::Builder::ColumnList

NAME

SQL::Builder::ColumnList - generate a list of expressions to be used in a SELECT statement's column list

SYNOPSIS

        ( anything [ [AS] [alias]] [, ...] ) | *

This class is little more than a SQL::Builder::List(3) with some useful checks built into sql()

        # generate list of columns/expressions to be used
        my $col1 = SQL::Builder::Column->new(
                col => "foozle",
                alias => col1"
        );

        my $col2 = SQL::Builder::Column->new(col => "bang");

        my $col3 = "fosheezy";

        my $expr = SQL::Builder::BinaryOp->new(
                op => "+",
                opers => ["15", $col3]
        );

        my $list = SQL::Builder::ColumnList->new(
                cols => [$col1, $col2, $col3, $expr]
        );

        # foozle AS col1, bang, fosheezy, 15 + fosheezy
        print $list->sql;

        # turn of the 'AS' keyword
        $list->use_as(0);

        # foozle col1, bang, fosheezy, 15 + fosheezy
        print $list->sql;

        # turn off aliases completely
        $list->use_aliases(0);
        
        # foozle, bang, fosheezy, 15 + fosheezy
        print $list->sql;

        # Let's get all columns
        $list->list_clear();

        # *
        print $list->sql;

        # set $col3 as our default column
        $list->default_select($col3);

        # fosheezy
        print $list->sql;

DESCRIPTION

This is a subclass of SQL::Builder::List(3). It will probably the most useful when used for generating the column list returned from a SELECT statement. Any object in the maintained list of expressions with an alias() method that returns something defined() and with a length() will be used pending the current options.

METHODS

new()

See SQL::Builder::Base::new() and SQL::Builder::Base::set() - as they are inherited

cols([@list])

Use this to get/set the list of expressions. This is really just a wrapper to SQL::Builder::List::list(), see it for more documentation

default_select([$default_select])

This sets the default select expression which is used when list() or cols() returns an empty list. If $default_select is passed, it sets the default select expression and returns the current object. With no arguments, it returns the current value

init()

This calls SQL::Builder::List::init() and sets some default options, including use_as(1) and use_aliases(1)

sql()

To summarize, every expression (be it the column expression or its alias) is passed through SQL::Builder::Base::dosql(). SQL::Builder::Column objects are treated specially and SQL::Builder::Column::full_name() is used as the expression. Aliases are only considered valid when they are defined and have a length. When the list of expressions is empty, default_select() is checked; if default_select()'s return value is not defined, "*" is returned by sql(). The return value of default_select() is passed through dosql() as well. In the even any usable alias is found, use_as() is checked: when it is true, the 'AS' keyword is used between the expression and its alias.

If that wasn't enough, please read the following, more confusing and wordy description of how this method behaves:

This method overwrites the inherited sql(). If list() returns an empty list, then default_select() is checked. If default_select() is defined() and has a length(), then the value of $self->dosql($self->default_select) is used. If the returned value of default_select() is not defined, "*" is used as the default selection expression. If the value is defined but has no length, en empty string is returned by sql().

If list() does have elements, then use_aliases() is checked. If use_aliases() is true, then expressions in the list that inherit from SQL::Builder::Column(3) are checked for aliases that are defined() and have a length(), in which case they will be used; if the alias is not valid, SQL::Builder::Column::full_name() is used -- in either case, the return of full_name() will be processed with dosql().

When an expression from list() is not a SQL::Builder::Column(3) object, it is checked for an alias() method, and used if its return is defined and has a length. The expression is always passed through SQL::Builder::Base::dosql().

When use_aliases() is turned off, all expressions are passed through SQL::Builder::Base::dosql() with the exception of SQL::Builder::Column objects. If these are encountered, SQL::Builder::Column::full_name() is passed through SQL::Builder::Base::dosql()

use_aliases([1|0])

This method controls the option to use expression aliases when they're available. When called with no arguments, the current value is returned. Pass a true or false value to turn it on or off, respectively

use_as([1|0])

This method controls the option to use the 'AS' keyword between an expression and its alias upon SQL serialization (sql()). Called with no arguments, this method returns the current value. Pass a 1 or 0 to turn it on or off, respectively. When passing a value, the current object is returned

children

If there are any items in list(), SQL::Builder::List::children() is returned. If the list is empty and default_select() is defined, an iterator containing the default_select() value is returned. Otherwise, an empty list is returned

SEE ALSO

SQL::Builder::Column(3) SQL::Builder::List(3) SQL::Builder::Base(3)