Emanuele Zeppieri > DBIx-MultiStatementDo-1.00009 > DBIx::MultiStatementDo

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Module Version: 1.00009   Source  

NAME ^

DBIx::MultiStatementDo - Multiple SQL statements in a single do() call with any DBI driver

VERSION ^

version 1.00009

SYNOPSIS ^

    use DBI;
    use DBIx::MultiStatementDo;
    
    # Multiple SQL statements in a single string
    my $sql_code = <<'SQL';
    CREATE TABLE parent (a, b, c   , d    );
    CREATE TABLE child (x, y, "w;", "z;z");
    /* C-style comment; */
    CREATE TRIGGER "check;delete;parent;" BEFORE DELETE ON parent WHEN
        EXISTS (SELECT 1 FROM child WHERE old.a = x AND old.b = y)
    BEGIN
        SELECT RAISE(ABORT, 'constraint failed;'); -- Inlined SQL comment
    END;
    -- Standalone SQL; comment; w/ semicolons;
    INSERT INTO parent (a, b, c, d) VALUES ('pippo;', 'pluto;', NULL, NULL);
    SQL
    
    my $dbh = DBI->connect( 'dbi:SQLite:dbname=my.db', '', '' );
    
    my $batch = DBIx::MultiStatementDo->new( dbh => $dbh );
    
    # Multiple SQL statements in a single call
    my @results = $batch->do( $sql_code )
        or die $batch->dbh->errstr;
    
    print scalar(@results) . ' statements successfully executed!';
    # 4 statements successfully executed!

DESCRIPTION ^

Some DBI drivers don't support the execution of multiple statements in a single do() call. This module tries to overcome such limitation, letting you execute any number of SQL statements (of any kind, not only DDL statements) in a single batch, with any DBI driver.

Here is how DBIx::MultiStatementDo works: behind the scenes it parses the SQL code, splits it into the atomic statements it is composed of and executes them one by one. To split the SQL code SQL::SplitStatement is used, which uses a more sophisticated logic than a raw split on the ; (semicolon) character: first, various different statement terminator tokens are recognized, then SQL::SplitStatement is able to correctly handle the presence of said tokens inside identifiers, values, comments, BEGIN ... END blocks (even nested), dollar-quoted strings, MySQL custom DELIMITERs, procedural code etc., as (partially) exemplified in the "SYNOPSIS" above.

Automatic transactions support is offered by default, so that you'll have the all-or-nothing behaviour you would probably expect; if you prefer, you can anyway disable it and manage the transactions yourself.

METHODS ^

new

It creates and returns a new DBIx::MultiStatementDo object. It accepts its options either as an hash or an hashref.

The following options are recognized:

do

This is the method which actually executes the SQL statements against your db. As its first (mandatory) argument, it takes an SQL string containing one or more SQL statements. The SQL string is split into its atomic statements, which are then executed one-by-one, in the same order they appear in the given string.

The first argument can also be a reference to a list of (already split) statements, in which case no split is performed and the statements are executed as they appear in the list. The list can also be a two-elements list, where the first element is the statements listref as above, and the second is the placeholder numbers listref, exactly as returned by the SQL::SplitStatement::split_with_placeholders() method.

Analogously to DBI's do(), it optionally also takes an hashref of attributes (which is passed unaltered to $batch->dbh->do() for each atomic statement), and the bind values, either as a listref or a flat list (see below for the difference).

In list context, do returns a list containing the values returned by the $batch->dbh->do() call on each single atomic statement.

If the rollback option has been set (and therefore automatic transactions are enabled), in case one of the atomic statements fails, all the other succeeding statements executed so far, if any, are rolled back and the method (immediately) returns an empty list (since no statements have actually been committed).

If the rollback option is set to a false value (and therefore automatic transactions are disabled), the method immediately returns at the first failing statement as above, but it does not roll back any prior succeeding statement, and therefore a list containing the values returned by the statements (successfully) executed so far is returned (and these statements are actually committed to the db, if $dbh->{AutoCommit} is set).

In scalar context it returns, regardless of the value of the rollback option, undef if any of the atomic statements failed, or a true value if all of the atomic statements succeeded.

Note that to activate the automatic transactions you don't have to do anything more than setting the rollback option to a true value (or simply do nothing, as it is the default): DBIx::MultiStatementDo will automatically (and temporarily, via local) set $dbh->{AutoCommit} and $dbh->{RaiseError} as needed. No other DBI db handle attribute is ever touched, so that you can for example set $dbh->{PrintError} and enjoy its effects in case of a failing statement.

If you want to disable the automatic transactions and manage them by yourself, you can do something along this:

    my $batch = DBIx::MultiStatementDo->new(
        dbh      => $dbh,
        rollback => 0
    );
    
    my @results;
    
    $batch->dbh->{AutoCommit} = 0;
    $batch->dbh->{RaiseError} = 1;
    eval {
        @results = $batch->do( $sql_string );
        $batch->dbh->commit;
        1
    } or eval {
        $batch->dbh->rollback
    };

Bind Values as a List Reference

The bind values can be passed as a reference to a list of listrefs, each of which contains the bind values for the atomic statement it corresponds to. The bind values inner lists must match the corresponding atomic statements as returned by the internal splitter object, with undef (or empty listref) elements where the corresponding atomic statements have no placeholders.

Here is an example:

    # 7 statements (SQLite valid SQL)
    my $sql_code = <<'SQL';
    CREATE TABLE state (id, name);
    INSERT INTO  state (id, name) VALUES (?, ?);
    CREATE TABLE city (id, name, state_id);
    INSERT INTO  city (id, name, state_id) VALUES (?, ?, ?);
    INSERT INTO  city (id, name, state_id) VALUES (?, ?, ?);
    DROP TABLE city;
    DROP TABLE state
    SQL
    
    # Only 5 elements are required in the bind values list
    my $bind_values = [
        undef                  , # or []
        [ 1, 'Nevada' ]        ,
        []                     , # or undef
        [ 1, 'Las Vegas'  , 1 ],
        [ 2, 'Carson City', 1 ]
    ];
    
    my $batch = DBIx::MultiStatementDo->new( dbh => $dbh );
    
    my @results = $batch->do( $sql_code, undef, $bind_values )
        or die $batch->dbh->errstr;

If the last statements have no placeholders, the corresponding undefs don't need to be present in the bind values list, as shown above. The bind values list can also have more elements than the number of the atomic statements, in which case the excess elements will simply be ignored.

Bind Values as a Flat List

This is a much more powerful feature of do: when it gets the bind values as a flat list, it automatically assigns them to the corresponding placeholders (no interleaving undefs are necessary in this case).

In other words, you can regard the given SQL code as a single big statement and pass the bind values exactly as you would do with the ordinary DBI do method.

For example, given $sql_code from the example above, you could simply do:

    my @bind_values = ( 1, 'Nevada', 1, 'Las Vegas', 1, 2, 'Carson City', 1 );
    
    my @results = $batch->do( $sql_code, undef, @bind_values )
        or die $batch->dbh->errstr;

and get exactly the same result.

Difference between Bind Values as a List Reference and as a Flat List

If you want to pass the bind values as a flat list as described above, you must pass the first parameter to do either as a string (so that the internal splitting is performed) or, if you want to disable the internal splitting, as a reference to the two-elements list containing both the statements and the placeholder numbers listrefs (as described above in do).

In other words, you can't pass the bind values as a flat list and pass at the same time the (already split) statements without the placeholder numbers listref. To do so, you need to pass the bind values as a list reference instead, otherwise do throws an exception.

To summarize, bind values as a flat list is easier to use but it suffers from this subtle limitation, while bind values as a list reference is a little bit more cumbersome to use, but it has no limitations and can therefore always be used.

Recognized Placeholders

The recognized placeholders are:

dbh

rollback

splitter_options

split and split_with_placeholders

These are the methods used internally to split the given SQL code. They call respectively split and split_with_placeholders on a SQL::SplitStatement instance built with the splitter_options described above.

Normally they shouldn't be used directly, but they could be useful if you want to see how your SQL code has been split.

If you want instead to see how your SQL code will be split, that is before executing do, you can use SQL::SplitStatement by yourself:

    use SQL::SplitStatement;
    my $splitter = SQL::SplitStatement->new( \%splitter_options );
    my @statements = $splitter->split( $sql_code );
    # Now you can check @statements if you want...

and then you can execute your statements preventing do from performing the splitting again, by passing \@statements to it:

    my $batch = DBIx::MultiStatementDo->new( dbh => $dbh );
    my @results = $batch->do( \@statements ); # This does not perform the splitting again.

Warning! In previous versions, the split_with_placeholders (public) method documented above did not work, so there is the possibility that someone used the (private, undocumented) _split_with_placeholders method instead (which worked correctly). In this case, please start using the public method (which now works as advertised), since the private method will be removed in future versions.

LIMITATIONS ^

Please look at: SQL::SplitStatement LIMITATIONS

DEPENDENCIES ^

DBIx::MultiStatementDo depends on the following modules:

AUTHOR ^

Emanuele Zeppieri, <emazep@cpan.org>

BUGS ^

No known bugs so far.

Please report any bugs or feature requests to bug-dbix-MultiStatementDo at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=DBIx-MultiStatementDo. I will be notified, and then you'll 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 DBIx::MultiStatementDo

You can also look for information at:

ACKNOWLEDGEMENTS ^

Matt S Trout, for having suggested a much more suitable name for this module.

SEE ALSO ^

LICENSE AND COPYRIGHT ^

Copyright 2010-2011 Emanuele Zeppieri.

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation, or the Artistic License.

See http://dev.perl.org/licenses/ for more information.

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