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SQL::Eval

Section: User Contributed Perl Documentation (3)
Updated: perl v5.6.0
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NAME

SQL::Eval - Base for deriving evalution 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 derivingconcrete subclasses to evaluate SQL::Statement objects. TheSQL::Eval object can be thought as an abstract state engine forexecuting SQL queries, the SQL::Eval::Table object can be considereda *very* table abstraction. It implements method for fetching orstoring rows, retrieving column names and numbers and so on.See the `test.pl' script as an example for implementing a concretesubclass.

While reading on, keep in mind that these are abstract classes,you *must* implement at least some of the methods describe below.Even more, you need not derive from SQL::Eval or SQL::Eval::Table,you just need to implement the method interface.

All methods just 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

Likewise used for getting or setting the complete array of inputparameters. 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 and just 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 asubclass).

row

Used to get the current row as an array ref. Do not mismatchgetting the current row with the fetch_row method! In fact thismethod is valid only after a successfull `$table->fetchrow()'.Example:

    $row = $table->row();

column

Get the column with a given name in the current row. Valid only aftera successfull `$table->fetchrow()'. Example:

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

column_num

Return the number of the given column name. Column numbers start with0. Returns undef, if a column name is not defined, so that you canwell use this for verifying valid column names. Example:

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

column_names

Returns an array ref of column names.

The above methods are implemented by SQL::Eval::Table. The followingmethods aren't, so that they *must* be implemented by concretesubclassed. See the `test.pl' script for example.

fetch_row

Fetches the next row from the table. Returns `undef', if the lastrow was already fetched. The argument $data is for private use ofthe concrete 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'.

push_row

Likewise for storing rows. Example:

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

push_names

Used by the CREATE TABLE statement to set the column names of thenew 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 numberof the next row being written. Example:

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

Actually the current implementation is using only `seek($data, 0,0)'(first row) and `seek($data, 2,0)' (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 anhash ref with only two attributes. The `params' attribute is an arrayref of parameters. The `tables' attribute is an hash ref of tablenames (keys) and table objects (values).

SQL::Eval::Table instances are implemented as hash refs. Used attributesare `row' (the array ref of the current row), `col_nums' (an hash refof 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 moduleis reentrant and thread safe, if you either don't share handles betweenthreads or grant serialized use.

AUTHOR AND COPYRIGHT

    Jochen Wiedmann    Am Eisteich 9    72555 Metzingen    Germany

    Email: joeAATTispsoft.de    Phone: +49 7123 14887

You may distribute this module under the terms of either the GNUGeneral Public License or the Artistic License, as specified inthe Perl README file.

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