NAME

DBD::Informix - Access to Informix Databases

SYNOPSIS

use DBD::Informix;

DESCRIPTION

This document describes DBD::Informix version 0.25 and later.

It has a biassed view on how to use DBI and DBD::Informix. Because there is no better documentation of how to use DBI, this covers both DBI and DBD::Informix. The extant documentation on DBI suggests that things should be done differently, but gives no solid examples of how it should be done differently or why it should be done differently.

Be aware that on occasion, it gets complex because of differences between different versions of Informix software. The key factor is the version of ESQL/C used when building DBD::Informix. Basically, there are two groups of versions to worry about, the 5.0x family of versions (5.00.UC1 through 5.08.UC1 at the moment), and the 6.0x and later family of versions (6.00.UE1 through 7.21.UC1 at the moment). All version families acquire extra versions on occasion.

Note that DBD::Informix does not work with 4.1x or earlier versions of ESQL/C because it uses SQL descriptors and these are not available prior to version 5.00.

USE OF DBD::Informix

Loading DBD::Informix

To use the DBD::Informix software, you need to load the DBI software and then install the Informix driver:

use DBI;
$drh = DBI->install_driver('Informix');

This gives you a reference to the driver, aka the driver handle. If the load fails, your program stops immediately (unless, perhaps, you eval the statement).

Once you have the driver handle, you can interrogate the driver for some basic information:

print "Driver Information\n";
# Type is always 'dr'.
print "    Type:                  $drh->{Type}\n";
# Name is always 'Informix'.
print "    Name:                  $drh->{Name}\n";
# Version is the version of DBD::Informix (eg 0.25).
print "    Version:               $drh->{Version}\n";
# The ProductName is the version of ESQL/C; it corresponds to
# the first line of the output from "esql -V".
print "    Product:               $drh->{ProductName}\n";
# The ProductVersion is an integer version number such as 721
# for ESQL/C version 7.21.UC1.
print "    Product Version:       $drh->{ProductVersion}\n";
# The Attribution identifies the culprits who provided you
# with this software.
print "    Attribution:           $drh->{Attribution}\n";
# The MultipleConnections indicates whether the driver
# supports multiple connections (1) or not (0).
print "    Multiple Connections:  $drh->{MultipleConnections}\n";

# -- Not implemented in DBD::Informix 0.25 --
# ActiveConnections identifies the number of open connections.
print "    Active Connections:      $drh->{ActiveConnections}\n";
# CurrentConnection identifies the current connection.
print "    Current Connections:     $drh->{CurrentConnection}\n";

Once you have the driver loaded, you can connect to a database, or you can (in theory) sever all connections to databases with disconnect_all, but this has not been implemented in 0.25b2.

$drh->disconnect_all;

There is also an unofficial function which can be called using:

@dbnames = $drh->func('_ListDBs');

You can test whether this worked with:

if (defined @dbnames) { ...process array... }
else                  { ...process error... }

CONNECTING TO A DATABASE

To connect to a database, you can use the connect function, which yields a valid reference or database handle if it is successful (and aborts the script if it is not successful). FWIW: the abort is done by DBI, not by DBD::Informix.

$dbh = $drh->connect($database, $username, $password);

The 5.0x versions ignore the username and password data, and the statement is equivalent to: EXEC SQL DATABASE :database;

The 6.0x versions only use the username and password if both are supplied, but it is equivalent to:

EXEC SQL CONNECT TO :database AS :connection
    USER :username USING :password
    WITH CONCURRENT TRANSACTIONS

The connection is given a name by DBD::Informix.

For Informix, the database name is any valid format for the DATABASE or CONNECT statements. Examples include:

dbase               # 'Local' database
//machine1/dbase    # Database on remote machine
dbase@server1       # Database on (remote) server (as defined in sqlhosts)
@server1            # Connection to (remote) server but no database
/some/where/dbase   # Connect to local SE database

The database name is not supplied implicitly. Contrary to some other documentation, the DBD::Informix code does not default the database to the value in %ENV{PERL_DBI_DATABASE}.

Once you have a database handle, you can interrogate it for some basic information about the database, etc.

print "Database Information\n";
# Type is always 'db'
print "    Type:                    $dbh->{Type}\n";
# Name is the name of the database specified at connect
print "    Database Name:           $dbh->{Name}\n";
# InformixOnLine is 1 (true) if the handle is connected to an
# Informix-OnLine server.
print "    Informix-OnLine:         $dbh->{InformixOnLine}\n";
# LoggedDatabase is 1 (true) if the database has
# transactions.
print "    Logged Database:         $dbh->{LoggedDatabase}\n";
# ModeAnsiDatabase is 1 (true) if the database is MODE ANSI.
print "    Mode ANSI Database:      $dbh->{ModeAnsiDatabase}\n";
# AutoCommit is 1 (true) if the database commits each
# statement.
print "    AutoCommit:              $dbh->{AutoCommit}\n";
# AutoErrorReport is 1 (true) if errors are reported as they
# are detected.
print "    AutoErrorReport:         $dbh->{AutoErrorReport}\n";
# InTransaction is 1 (true) if the database is in a transaction
print "    Transaction Active:      $dbh->{InTransaction}\n";

If $dbh->{AutoErrorReport} is true, then DBD::Informix will report each error automatically on STDERR when it is detected. The error is also available via the package variables $DBI::errstr and $DBI::err. Note that $DBI::errstr includes the SQL error number and the ISAM error number if there is one, and ends with a newline. The message may or may not extend over several lines, and is generally formatted so that it will display neatly within 80 columns.

If $dbh->{AutoErrorReport} is false, then DBD::Informix does not report any errors when it detects them; it is up to the user to note that errors have occurred and to report them.

If you have forgotten the driver, you can discover it again using:

$drh = $dbh->{Driver};

BUG: The name of the database should be tracked more carefully via the DATABASE, CLOSE DATABASE, CREATE DATABASE, ROLLFORWARD DATABASE and START DATABASE statements. Note that you cannot prepare CONNECT statements, so they do not have to be tracked.

= back

DISCONNECTING FROM A DATABASE

You can also disconnect from the database:

$dbh->disconnect;

This will rollback any uncommitted work. Note that this does not destroy the database handle. You need to do an explicit 'undef $dbh' to destroy the handle. Any statements prepared using this handle are finished (see below) and cannot be used again. All space associated with the statements is released.

If you are using an Informix driver for which $drh->{ProductVersion} >= 600, then you can have multiple concurrent connections. This means that multiple calls to $drh->connect will give you independent connections to one or more databases.

If you are using an Informix driver for which $drh->{ProductVersion} < 600, then you cannot have multiple concurrent connections. If you make multiple calls to $drh->connect, you will achieve the same effect as executing several database statements in a row. This will generally switch databases successfully, but may invalidate any statements previously prepared. It may fail if the current database is not local, or if there is an active transaction, etc.

SIMPLE STATEMENTS

Given a database connection, you can execute a variety of simple statements using a variety of different calls:

$dbh->commit;
$dbh->rollback;

These two operations commit or rollback the current transaction. If the database is unlogged, they do nothing. If the database is not MODE ANSI and AutoCommit is set to 0 then a new transaction is automatically started. If the database is not MODE ANSI and AutoCommit is set to 1 (the default), then no explicit transaction is started.

You can execute most preparable parameterless statements using:

$dbh->do($stmt);

The statement must not be either SELECT (other than SELECT...INTO TEMP) or EXECUTE PROCEDURE where the procedure returns data. This will use the ESQL/C EXECUTE IMMEDIATE statement.

You can execute an arbitrary statement with parameters using:

$dbh->do($stmt, @parameters);
$dbh->do($stmt, $param1, $param2);

Again, the statement must not be a SELECT or EXECUTE PROCEDURE which returns data. The values in @parameters (or the separate values) are bound to the question marks in the statement string. However, this cannot use EXECUTE IMMEDIATE because it does not accept parameters.

$sth = $dbh->prepare($stmt);
$sth->execute(@parameters);

Unlike previous releases, which used some code from the DBI package, DBD::Informix v0.26, now handles the 'do' operation exclusively with its own code.

BUG: If the statement you run is a SELECT, then it is prepared, and the cursor is declared, opened (potentially expensive, if the statement uses ORDER BY etc), and then closed and freed without fetching any data. A more robust version would generate an error condition without declaring the cursor, etc.

= back

You can embed an arbitrary string inside a statement with any quote marks correctly handled by invoking:

$dbh->quote($string);

This method is provided by the DBI package implementation and is inherited by the DBD::Informix package. The string is enclosed in singel quotes, and any embedded single quotes are doubled up, which conforms to the SQL-92 standard.

CREATING STATEMENTS

You can also prepare a statement for multiple uses, and you can do this for SELECT and EXECUTE PROCEDURE statements which return data (cursory statements) as well as non-cursory statements which return no data. You create a statement handle (another reference) using:

$sth = $dbh->prepare($stmt);

If the statement is a SELECT which returns data (not SELECT...INTO TEMP) or an EXECUTE PROCEDURE for a procedure which returns values, then a cursor is declared for the prepared statement.

According to the DBI specification, the prepare call accepts an optional attributes parameter which is a reference to a hash. At the moment, no parameters are recognized. It would be reasonable to add, for example, {CursorWithHold => 1} to specify that the cursor should be declared WITH HOLD. Similarly, you could add {BlobLocation => 'InFile'} to support per-statement blob location, and {ScrollCursor => 1} to support scroll cursors.

Note: in versions of DBD::Informix prior to 0.25, preparing a statement also executed non-cursory statements and opened the cursor for cursory statements. This no longer occurs.

More typically, you need to do error checking, and this is achieved by using:

die "Failed to prepare '$stmt'\n"
    unless ($sth = $dbh->prepare($stmt));

BUG: There is no way to tell whether the statement is just executable or whether it is a cursory (fetchable) statement. You are assumed to know.

= back

Once the statement is prepared, you can execute it:

$sth->execute;

For a non-cursory statement, this simply executes the statement. For a cursory statement, it opens the cursor. You can also specify the parameters for a statement using:

$sth->execute(@parameters);

The first parameter will be supplied as the value for the first place-holder question mark in the statement, the second parameter for the second place-holder, etc.

Issue: At the moment, there is no checking by DBD::Informix on how many parameters are supplied and how many are needed. This needs to be resolved. Also, the Informix engines give no support for determining the types of those parameters except in the VALUES clause of an INSERT statement. This means that DBD::Informix v0.25 cannot handle blobs in the SET clause of an UPDATE statement.

BUG: The various bind routines defined by DBI (primarily to support DBD::Oracle) are not implemented in DBD::Informix because there are no clearly documented semantics associated with the calls.

= back

For cursory statements, you can discover what the returned column names, types, nullability, etc are. You do this with:

@name = @{$sth->{NAME}};        # Column names
@null = @{$sth->{NULLABLE}};    # True => accepts nulls
@type = @{$sth->{TYPE}};        # Data types with qualifiers
@prec = @{$sth->{PRECISION}};   # Numeric length from SysColumns.Collength
@scal = @{$sth->{SCALE}};       # Same as PRECISION

BUG: PRECISION is not clearly defined, and neither is SCALE. It isn't clear which types should have a these attributes. There should, probably, be $sth->{ColLength} to do what $sth->{PRECISION} and $sth->{SCALE} do, and the precision and scale should be defined for FLOAT, SMALLFLOAT, DECIMAL, MONEY types and their synonyms. It is not clear whether the various types of integer values should be given precision and scale values, though it is relatively easy to define valid values for them. It is not clear how floating point numbers are represented in SCALE. It is not clear whether the various CHAR types should be given a PRECISION corresponding to their length. Etc... This is one point where the DBI specification is badly in need of definition.

BUG: You might be able to do the same with INSERT statements, except that some internal machinations mean that it probably does not work in 0.25.

= back

If the statement is a cursory statement, you can retrieve the values in either of two ways:

$ref = $sth->fetch;
@row = @{$ref};

@row = @{$sth->fetch};  # Shorthand for above...

@row = $sth->fetchrow;

As usual, you have to worry about whether this worked or not. You would normally, therefore, use:

    while ($ref = $sth->fetch)
    {
        # We know we got some data here
        ...
    }
    # Investigate whether an error occurred or the SELECT
	# simply had nothing more to return.
    if ($sth->{sqlcode} < 0)
    {
        # Process error...
    }

The returned data includes blobs mapped into strings. Note that byte blobs might contain ASCII NUL '\0' characters. Perl knows how long the strings are and does preserve NUL in the middle of a byte blob. However, you may need to be careful deciding how to handle this string.

There is provision to specify how you want blobs handled. You can set the attribute:

$sth->{BlobLocation} = 'InMemory';      # Default
$sth->{BlobLocation} = 'InFile';        # In a named file
$sth->{BlobLocation} = 'DummyValue';    # Return dummy values
$sth->{BlobLocation} = 'NullValue';     # Return undefined

The InFile mode returns the name of a file in the fetched array, and that file can be accessed by Perl using normal file access methods. The DummyValue mode returns "<<TEXT VALUE>>" for text blobs or "<<BYTE VALUE>>" for byte (binary) blobs. The NullValue mode returns undefined (meaning that Perl's "defined" operator would return false) values. Note that these two options do not necessarily prevent the Server from returning the data to the application, but the user does not get to see the data -- this depends on the internal implementation of the ESQL/C FETCH operation in conjunction with SQL descriptors.

You can also set the BlobLocation attribute on the database, overriding it at the statement level.

BUG: BlobLocation is not honoured.

= back

When you have fetched as many rows as required, you close the cursor using:

$sth->finish;

This simply closes the cursor; it does not free the cursor or the statement. That is done when you destroy (undef) the statement handle:

undef $sth;

You can also implicitly rebind a statement handle to a new statement by simply using the same variable again. This does not cause any memory leaks.

TRANSACTION MANAGEMENT

The Interactions of AutoCommit with Informix Databases

There are 3 types of Informix database to consider: MODE ANSI, Logged, UnLogged. Although MODE ANSI databases also have a transaction log, the category of Logged databases specifically excludes MODE ANSI databases. In OnLine, this refers to databases created WITH LOG or WITH BUFFERED LOG; in SE, to databases created WITH LOG IN "/some/file/name".

There are 2 AutoCommit modes to consider: On, Off.

There are 2 possible transaction states: In-TX (In transaction), No-TX (Outside transaction).

There are at least 13 types of statement (in 4 groups and 9 sub-groups) to consider:

• $drh->connect('xyz'); # Group 1A

• $dbh->do('DATABASE xyz'); # Group 1B

• $dbh->do('CREATE DATABASE xyz'); # Group 1B

• $dbh->do('ROLLFORWARD DATABASE xyz'); # Group 1B

• $dbh->do('START DATABASE xyz'); # Group 1B

• $dbh->disconnect(); # Group 2A

• $dbh->do('CLOSE DATABASE'); # Group 2B

• $dbh->commit(); # Group 3A

• $dbh->rollback(); # Group 3A

• $dbh->do('BEGIN WORK'); # Group 3B

• $dbh->do('ROLLBACK WORK'); # Group 3C

• $dbh->do('COMMIT WORK'); # Group 3C

• $dbh->prepare('SELECT ...'); # Group 4A

• $dbh->prepare('UPDATE ...'); # Group 4B

The Group 1 statements establish the default AutoCommit mode for a database handle. Group 1A is the primary means of connecting to a database; the Group 1B statements can change the default AutoCommit mode by virtue of changing the current database.

For a MODE ANSI database, the default AutoCommit mode is Off. For a Logged database, the default AutoCommit mode is On. For an UnLogged database, the default AutoCommit mode is On and it cannot be changed. Any attempt to change AutoCommit mode to Off with an UnLogged database generates a non-fatal warning.

The Group 2 statements sever the connection to a database. The Group 2A statement renders the database handle unusable; no further operations are possible except 'undef' or re-assigning with a new connection. The Group 2B statement means that no operations other than those in Group 1B or 'DROP DATABASE' are permitted. The value of AutoCommit is irrelevant after the database is closed.

The Group 3 & 4 statements interact in many complicated ways. Although UPDATE is cited in Group 4B, it represents any statement which is not a SELECT statement. Note that 'SELECT ... INTO TEMP' is a Group 4B statement because it returns no data to the program. An 'EXECUTE PROCEDURE' statement is in Group 4A if it returns data, and in Group 4B if it does not, and you cannot tell which of the two groups applies until after the statement is prepared.

MODE ANSI Databases

By default, a MODE ANSI database operates with AutoCommit Off. When the connection is established, a transaction is started implicitly, and the program will be inside a transaction (In-TX) at all times. Whenever either of the group 3A functions is used, a new transaction is automatically (but implicitly) started. The DBD::Informix code does not do an explicit BEGIN WORK because the user is entitled to write their own BEGIN WORK immediately after COMMIT WORK or ROLLBACK WORK (and hence $dbh->commit or $dbh->rollback), and if DBD::Informix did this, the user would get an unwarranted error. Before disconnecting, the code does ROLLBACK WORK to ensure that the disconnect can occur cleanly.

If the user elects to switch to AutoCommit On, things get trickier. All cursors need to be declared WITH HOLD so that Group 4B statements being committed do not close the active cursors. Whenever a Group 4B statement is executed, the statement needs to be committed. With OnLine (and theoretically with SE, I think), if the statement fails there is no need to do a rollback -- the statement failing did the rollback anyway. And the commit will automatically start a new transaction. As before, the code can do ROLLBACK WORK before disconnecting, though it should not actually be necessary.

BUG: DBD::Informix does not create WITH HOLD cursors for MODE ANSI databases when AutoCommit mode is On.

= back

Logged Databases

Unlike MODE ANSI databases, Logged databases can be in either one of two transaction states -- In-TX and No-TX.

AutoCommit is set to On when the connection is established, and the transaction state is No-TX. No further action is required by DBD::Informix in this state. Neither $dbh->commit nor $dbh->rollback should be used in this state -- there is no transaction for them to work on. If they are called, the effect will be a no-op; all previous operations were already committed or rolled back, so they will succeed. Note that cursors established in this state are not declared WITH HOLD. If the user executes $dbh->do('BEGIN WORK') or equivalent, then the AutoCommit functionality is suspended and the transaction state is In-TX until the transaction is terminated. If a Group 3A function is executed, a new transaction is not started explicitly and the transaction state is once more No-TX, and the user can execute BEGIN WORK as required. If the state at $dbh->disconnect is In-TX, then DBD::Informix does a rollback before attempting to disconnect. If the user attempts to close the database (or open a new one) while in the In-TX state, an error will be generated by Informix.

If the user sets AutoCommit off explicitly, DBD::Informix does an explicit BEGIN WORK to start a transaction and the transaction state is In-TX (and will stay like that until AutoCommit is set to On). Cursors declared while AutoCommit is off do not need to be declared WITH HOLD either, so cursors in Logged databases are not WITH HOLD regardless of AutoCommit. However, it might be a good option to allow $dbh->{CursorsWithHold} to indicate that they are to be declared WITH HOLD. When the user executes a Group 3A function, a new transaction is started explicitly (meaning that the user cannot successfully execute BEGIN WORK) and the transaction state is In-TX.

UnLogged Databases

The transaction state is No-TX and AutoCommit is On, and this cannot be changed. Any attempt to set AutoCommit to Off generates a non-fatal warning but the program will continue; setting it to On generates neither a warning nor an error. Both $dbh->commit and $dbh->rollback succeed but do nothing. Executing any Group 3B or 3C statement will generate an error.

KNOWN RESTRICTIONS

• Blobs can only be located in memory (reliably).

• Some driver attributes (notably CurrentConnection and ActiveConnections) cannot be queried.

AUTHOR

At various times:

• Tim Bunce (Tim.Bunce@ig.co.uk)

• Alligator Descartes (descartes@hermetica.com)

• Jonathan Leffler (johnl@informix.com)

SEE ALSO

perl(1).

cpanm DBD::InformixTest

perl -MCPAN -e shell
install DBD::InformixTest