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

Provided by: libsql-statement-perl_1.414-1_all

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');

_gen_access_fastpath
Return a subroutine reference for fast accessing columns for read-only access.
This routine simply returns the "_gen_access_fastpath" of the referenced table.

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":

col_names Array reference containing the names of the columns in order they
appear in the table. This attribute must be provided by the derived
class.

col_nums Hash reference containing the column names as keys and the column
indexes as values. If this is omitted (does not exist), it will be
created from "col_names".

capabilities
Hash reference containing additional capabilities.

_gen_access_fastpath
Return a subroutine reference for fast accessing columns for read-only
access. When the instantiated object does not provide own methods for
"column" and "column_num" a subroutine reference is returned which
directly access the internal data structures. For all other cases a
subroutine directly calling "$self->column($_[0])" is returned.

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:

update_one_row
Defines whether the table is able to update one single row. This
capability is used for backward compatibility and might have
(depending on table implementation) several limitations. Please
carefully study the documentation of the table or ask the author of
the table, if this information is not provided.

This capability is evaluated automatically on first request and must
not be handled by any derived classes.

update_specific_row
Defines if the table is able to update one single row, but keeps the
original content of the row to update.

This capability is evaluated automatically on first request and must
not be handled by derived classes.

update_current_row
Defines if the table is able to update the currently touched row. This
capability requires the capability of "inplace_update".

This capability is evaluated automatically on first request and must
not be handled by derived classes.

rowwise_update
Defines if the table is able to do row-wise updates which means one of
"update_one_row", "update_specific_row" or "update_current_row". The
"update_current_row" is only evaluated if the table has the
"inplace_update" capability.

This capability is evaluated automatically on first request and must
not be handled by derived classes.

inplace_update
Defines if an update of a row has side effects (capability is not
available) or can be done without harming any other currently running
task on the table.

Example: The table storage is using a hash on the "PRIMARY KEY" of the
table. Real perl hashes do not care when an item is updated while the
hash is traversed using "each". "SDBM_File" 1.06 has a bug, which does
not adjust the traversal pointer when an item is deleted.

"SQL::Statement::RAM::Table" recognizes such situations and adjusts
the traversal pointer.

This might not be possible for all implementations which can update
single rows.

This capability could be provided by a derived class only.

delete_one_row
Defines whether the table can delete one single row by it's content or
not.

This capability is evaluated automatically on first request and must
not be handled by derived classes.

delete_current_row
Defines whether a table can delete the current traversed row or not.
This capability requires the "inplace_delete" capability.

This capability is evaluated automatically on first request and must
not be handled by derived classes.

rowwise_delete
Defines if any row-wise delete operation is provided by the table.
"row-wise" delete capabilities are "delete_one_row" and
"delete_current_row".

This capability is evaluated automatically on first request and must
not be handled by derived classes.

inplace_delete
Defines if the deletion of a row has side effects (capability is not
available) or can be done without harming any other currently running
task on the table.

This capability should be provided by a derived class only.

insert_new_row
Defines if a table can easily insert a new row without need to seek or
truncate. This capability is provided by defining the table class
method "insert_new_row".

This capability is evaluated automatically on first request and must
not be handled by derived classes.

If the capabilities rowwise_update and insert_new_row are provided, the table
primitive "push_row" is not required anymore and may be omitted.

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 do not 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, 2017 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.

NAME

SYNOPSIS

DESCRIPTION

INTERNALS

MULTITHREADING

BUGS

SUPPORT

AUTHOR AND COPYRIGHT

SEE ALSO