SQL::Eval
SQL::Eval(3) User Contributed Perl Documentation SQL::Eval(3)
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 deriving con-
crete subclasses to evaluate SQL::Statement objects. The SQL::Eval
object can be thought as an abstract state engine for executing SQL
queries, the SQL::Eval::Table object can be considered a *very* table
abstraction. It implements method for fetching or storing rows,
retrieving column names and numbers and so on. See the "test.pl"
script as an example for implementing a concrete subclass.
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
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 and just a shorthand for
$col = $eval->table(’foo’)->column(’id’);
Method interface of SQL::Eval::Table
new Constructor; use it like this:
$eval = SQL::Eval::Table->new(\%attr);
Blesses the hash ref \%attr into the SQL::Eval::Table class
(or a subclass).
row Used to get the current row as an array ref. Do not mismatch
getting the current row with the fetch_row method! In fact
this method is valid only after a successfull "$ta-
ble->fetchrow()". Example:
$row = $table->row();
column Get the column with a given name in the current row. Valid
only after a successfull "$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 well 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 following
methods aren’t, so that they *must* be implemented by concrete sub-
classed. See the "test.pl" script for example.
fetch_row
Fetches the next row from the table. Returns "undef", if the
last row was already fetched. The argument $data is for pri-
vate use of the 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
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, $rowNum);
Actually the current implementation is using only "seek($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 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. Used
attributes 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.
AUTHOR AND COPYRIGHT
This module is Copyright (C) 1998 by
Jochen Wiedmann
Am Eisteich 9
72555 Metzingen
Germany
Email: joe@ispsoft.de
Phone: +49 7123 14887
All rights reserved.
You may distribute this module under the terms of either the GNU Gen-
eral Public License or the Artistic License, as specified in the Perl
README file.
SEE ALSO
SQL::Statement(3)
perl v5.8.8 2009-03-05 SQL::Eval(3)
