NAME¶

SQL::Eval - Base for deriving evaluation objects for SQL::Statement

SYNOPSIS¶

    require SQL::Statement;
    require SQL::Eval;
    # Create an SQL statement; use a concrete subclass of
    # SQL::Statement
    my $stmt = MyStatement->new("SELECT * FROM foo, bar",
                                SQL::Parser->new('Ansi'));
    # Get an eval object by calling open_tables; this
    # will call MyStatement::open_table
    my $eval = $stmt->open_tables($data);
    # Set parameter 0 to 'Van Gogh'
    $eval->param(0, 'Van Gogh');
    # Get parameter 2
    my $param = $eval->param(2);
    # Get the SQL::Eval::Table object referring the 'foo' table
    my $fooTable = $eval->table('foo');

DESCRIPTION¶

This module implements two classes that can be used for deriving subclasses to evaluate SQL::Statement objects. The SQL::Eval object can be thought as an abstract state engine for executing SQL queries and the SQL::Eval::Table object is a table abstraction. It implements methods for fetching or storing rows, retrieving column names and numbers and so on. See the "test.pl" script as an example for implementing a subclass. While reading on, keep in mind that these are abstract classes, you *must* implement at least some of the methods described below. In addition, you need not derive from SQL::Eval or SQL::Eval::Table, you just need to implement the method interface. All methods throw a Perl exception in case of errors.

Method interface of SQL::Eval¶

new

Constructor; use it like this:

 

    $eval = SQL::Eval->new(\%attr);
    

 

Blesses the hash ref \%attr into the SQL::Eval class (or a subclass).

param

Used for getting or setting input parameters, as in the SQL query

 

    INSERT INTO foo VALUES (?, ?);
    

 

Example:

 

    $eval->param(0, $val);        # Set parameter 0
    $eval->param(0);              # Get parameter 0
    

params

Used for getting or setting the complete array of input parameters. Example:

 

    $eval->params($params);       # Set the array
    $eval->params();              # Get the array
    

table

Returns or sets a table object. Example:

 

    $eval->table('foo', $fooTable);  # Set the 'foo' table object
    $eval->table('foo');             # Return the 'foo' table object
    

column

Return the value of a column with a given name; example:

 

    $col = $eval->column('foo', 'id');  # Return the 'id' column of
                                        # the current row in the
                                        # 'foo' table
    

 

This is equivalent to and a shorthand for

 

    $col = $eval->table('foo')->column('id');
    

Method interface of SQL::Eval::Table¶

new

Constructor; use it like this:

 

    $eval = SQL::Eval::Table->new(\%attr);
    

 

Blesses the hash ref \%attr into the SQL::Eval::Table class (or a subclass).

 

The following attributes are used by "SQL::Eval::Table":

row

Used to get the current row as an array ref. Do not confuse getting the current row with the fetch_row method! In fact this method is valid only after a successful "$table->fetchrow()". Example:

 

    $row = $table->row();
    

column

Get the column with a given name in the current row. Valid only after a successful "$table->fetchrow()". Example:

 

    $col = $table->column($colName);
    

column_num

Return the number of the given column name. Column numbers start with 0. Returns undef, if a column name is not defined, so that you can use this for verifying column names. Example:

 

    $colNum = $table->column_num($colNum);
    

col_nums

Returns an hash ref of column names with the column names as keys and the column indexes as the values.

col_names

Returns an array ref of column names ordered by their index within the table.

capability

Returns a boolean value whether the table has the specified capability or not. This method might be overridden by derived classes, but ensure that in that case the parent capability method is called when the derived class does not handle the requested capability.

 

The following capabilities are used (and requested) by SQL::Statement:

The above methods are implemented by SQL::Eval::Table. The following methods are not, so that they *must* be implemented by the subclass. See the "DBD::DBM::Table" or "DBD::CSV::Table" for example.

drop

Drops the table. All resources allocated by the table must be released after "$table-"drop($data)>.

fetch_row

Fetches the next row from the table. Returns "undef", if the last row was already fetched. The argument $data is for private use of the subclass. Example:

 

    $row = $table->fetch_row($data);
    

 

Note, that you may use

 

    $row = $table->row();
    

 

for retrieving the same row again, until the next call of "fetch_row".

 

"SQL::Statement" requires that the last fetched row is available again and again via "$table-" row()>.

push_row

As fetch_row except for storing rows. Example:

 

    $table->push_row($data, $row);
    

push_names

Used by the CREATE TABLE statement to set the column names of the new table. Receives an array ref of names. Example:

 

    $table->push_names($data, $names);
    

seek

Similar to the seek method of a filehandle; used for setting the number of the next row being written. Example:

 

    $table->seek($data, $whence, $rowNum);
    

 

Actually the current implementation only uses "seek($data, 0, 0)" (first row) and "seek($data, 2, 0)" (beyond last row, end of file).

truncate

Truncates a table after the current row. Example:

 

    $table->truncate($data);
    

INTERNALS¶

The current implementation is quite simple: An SQL::Eval object is an hash ref with only two attributes. The "params" attribute is an array ref of parameters. The "tables" attribute is an hash ref of table names (keys) and table objects (values). SQL::Eval::Table instances are implemented as hash refs. Attributes used are "row" (the array ref of the current row), "col_nums" (an hash ref of column names as keys and column numbers as values) and "col_names", an array ref of column names with the column numbers as indexes.

MULTITHREADING¶

All methods are working with instance-local data only, thus the module is reentrant and thread safe, if you either don't share handles between threads or grant serialized use.

BUGS¶

Please report any bugs or feature requests to "bug-sql-statement at rt.cpan.org", or through the web interface at <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=SQL-Statement>. I will be notified, and then you will automatically be notified of progress on your bug as I make changes.

SUPPORT¶

You can find documentation for this module with the perldoc command.

    perldoc SQL::Eval
    perldoc SQL::Statement

You can also look for information at:

•

RT: CPAN's request tracker

 

<http://rt.cpan.org/NoAuth/Bugs.html?Dist=SQL-Statement>

•

AnnoCPAN: Annotated CPAN documentation

 

<http://annocpan.org/dist/SQL-Statement>

•

CPAN Ratings

 

<http://cpanratings.perl.org/s/SQL-Statement>

•

Search CPAN

 

<http://search.cpan.org/dist/SQL-Statement/>

AUTHOR AND COPYRIGHT¶

Written by Jochen Wiedmann and currently maintained by Jens Rehsack. This module is Copyright (C) 1998 by

    Jochen Wiedmann
    Am Eisteich 9
    72555 Metzingen
    Germany
    Email: joe@ispsoft.de
    Phone: +49 7123 14887

and Copyright (C) 2009, 2010 by

     Jens Rehsack < rehsackATcpan.org>

All rights reserved. You may distribute this module under the terms of either the GNU General Public License or the Artistic License, as specified in the Perl README file.

SEE ALSO¶

SQL::Statement(3)