Exception::Class::DBI - DBI Exception objects

Author

       Original Author is David E. Wheeler <david@justatheory.com>

       Current maintainer is Graham Ollis <plicease@cpan.org>

Classes

Exception::Class::DBI creates a number of exception classes, each one specific to a particular DBI error
context. Most of the object methods described below correspond to like-named attributes in the DBI
itself. Thus the documentation below summarizes the DBI attribute documentation, so you should refer to
DBI itself for more in-depth information.

Exception::Class::DBI
All of the Exception::Class::DBI classes documented below inherit from Exception::Class::DBI. It offers
the several object methods in addition to those it inherits from its parent, Exception::Class. These
methods correspond to the DBI dynamic attributes, as well as to the values passed to the "handler()"
exception handler via the DBI "HandleError" attribute. Exceptions of this base class are only thrown when
there is no DBI handle object executing, e.g. in the DBI "connect()" method. Note: This functionality is
not yet implemented in DBI -- see the discusion that starts here:
<http://archive.develooper.com/dbi-dev@perl.org/msg01438.html>.

"error"
my $error = $ex->error;

Exception::Class::DBI actually inherits this method from Exception::Class. It contains the error
string that DBI prints when its "PrintError" attribute is enabled, or "die"s with when its
<RaiseError> attribute is enabled.

"err"
my $err = $ex->err;

Corresponds to the $DBI::err dynamic attribute. Returns the native database engine error code from
the last driver method called.

"errstr"
my $errstr = $ex->errstr;

Corresponds to the $DBI::errstr dynamic attribute. Returns the native database engine error message
from the last driver method called.

"state"
my $state = $ex->state;

Corresponds to the $DBI::state dynamic attribute. Returns an error code in the standard SQLSTATE five
character format.

"retval"
my $retval = $ex->retval;

The first value being returned by the DBI method that failed (typically "undef").

"handle"
my $db_handle = $ex->handle;

The DBI handle appropriate to the exception class. For Exception::Class::DBI::DRH, it will be a
driver handle. For Exception::Class::DBI::DBH it will be a database handle. And for
Exception::Class::DBI::STH it will be a statement handle. If there is no handle thrown in the
exception (because, say, the exception was thrown before a driver handle could be created), the
"handle" will be "undef".

Exception::Class::DBI::H
This class inherits from Exception::Class::DBI, and is the base class for all DBI handle exceptions (see
below). It will not be thrown directly. Its methods correspond to the DBI attributes common to all
handles.

"warn"
my $warn = $ex->warn;

Boolean value indicating whether DBI warnings have been enabled. Corresponds to the DBI "Warn"
attribute.

"active"
my $active = $ex->active;

Boolean value indicating whether the DBI handle that encountered the error is active. Corresponds to
the DBI "Active" attribute.

"kids"
my $kids = $ex->kids;

For a driver handle, Kids is the number of currently existing database handles that were created from
that driver handle. For a database handle, Kids is the number of currently existing statement handles
that were created from that database handle. Corresponds to the DBI "Kids" attribute.

"active_kids"
my $active_kids = $ex->active_kids;

Like "kids", but only counting those that are "active" (as above). Corresponds to the DBI
"ActiveKids" attribute.

"compat_mode"
my $compat_mode = $ex->compat_mode;

Boolean value indicating whether an emulation layer (such as Oraperl) enables compatible behavior in
the underlying driver (e.g., DBD::Oracle) for this handle. Corresponds to the DBI "CompatMode"
attribute.

"inactive_destroy"
my $inactive_destroy = $ex->inactive_destroy;

Boolean value indicating whether the DBI has disabled the database engine related effect of
"DESTROY"ing a handle. Corresponds to the DBI "InactiveDestroy" attribute.

"trace_level"
my $trace_level = $ex->trace_level;

Returns the DBI trace level set on the handle that encountered the error. Corresponds to the DBI
"TraceLevel" attribute.

"fetch_hash_key_name"
my $fetch_hash_key_name = $ex->fetch_hash_key_name;

Returns the attribute name the DBI "fetchrow_hashref()" method should use to get the field names for
the hash keys. Corresponds to the DBI "FetchHashKeyName" attribute.

"chop_blanks"
my $chop_blanks = $ex->chop_blanks;

Boolean value indicating whether DBI trims trailing space characters from fixed width character
(CHAR) fields. Corresponds to the DBI "ChopBlanks" attribute.

"long_read_len"
my $long_read_len = $ex->long_read_len;

Returns the maximum length of long fields ("blob", "memo", etc.) which the DBI driver will read from
the database automatically when it fetches each row of data. Corresponds to the DBI "LongReadLen"
attribute.

"long_trunc_ok"
my $long_trunc_ok = $ex->long_trunc_ok;

Boolean value indicating whether the DBI will truncate values it retrieves from long fields that are
longer than the value returned by "long_read_len()". Corresponds to the DBI "LongTruncOk" attribute.

"taint"
my $taint = $ex->taint;

Boolean value indicating whether data fetched from the database is considered tainted. Corresponds to
the DBI "Taint" attribute.

Exception::Class::DBI::DRH
DBI driver handle exceptions objects. This class inherits from Exception::Class::DBI::H, and offers no
extra methods of its own.

Exception::Class::DBI::DBH
DBI database handle exceptions objects. This class inherits from Exception::Class::DBI::H Its methods
correspond to the DBI database handle attributes.

"auto_commit"
my $auto_commit = $ex->auto_commit;

Returns true if the database handle "AutoCommit" attribute is enabled. meaning that database changes
cannot be rolled back. Corresponds to the DBI database handle "AutoCommit" attribute.

"db_name"
my $db_name = $ex->db_name;

Returns the "name" of the database. Corresponds to the DBI database handle "Name" attribute.

"statement"
my $statement = $ex->statement;

Returns the statement string passed to the most recent call to the DBI "prepare()" method in this
database handle. If it was the "prepare()" method that encountered the error and triggered the
exception, the statement string will be the statement passed to "prepare()". Corresponds to the DBI
database handle "Statement" attribute.

"row_cache_size"
my $row_cache_size = $ex->row_cache_size;

Returns the hint to the database driver indicating the size of the local row cache that the
application would like the driver to use for future "SELECT" statements. Corresponds to the DBI
database handle "RowCacheSize" attribute.

Exception::Class::DBI::STH
DBI statement handle exceptions objects. This class inherits from Exception::Class::DBI::H Its methods
correspond to the DBI statement handle attributes.

"num_of_fields"
my $num_of_fields = $ex->num_of_fields;

Returns the number of fields (columns) the prepared statement will return. Corresponds to the DBI
statement handle "NUM_OF_FIELDS" attribute.

"num_of_params"
my $num_of_params = $ex->num_of_params;

Returns the number of parameters (placeholders) in the prepared statement. Corresponds to the DBI
statement handle "NUM_OF_PARAMS" attribute.

"field_names"
my $field_names = $ex->field_names;

Returns a reference to an array of field names for each column. Corresponds to the DBI statement
handle "NAME" attribute.

"type"
my $type = $ex->type;

Returns a reference to an array of integer values for each column. The value indicates the data type
of the corresponding column. Corresponds to the DBI statement handle "TYPE" attribute.

"precision"
my $precision = $ex->precision;

Returns a reference to an array of integer values for each column. For non-numeric columns, the value
generally refers to either the maximum length or the defined length of the column. For numeric
columns, the value refers to the maximum number of significant digits used by the data type (without
considering a sign character or decimal point). Corresponds to the DBI statement handle "PRECISION"
attribute.

"scale"
my $scale = $ex->scale;

Returns a reference to an array of integer values for each column. Corresponds to the DBI statement
handle "SCALE" attribute.

"nullable"
my $nullable = $ex->nullable;

Returns a reference to an array indicating the possibility of each column returning a null. Possible
values are 0 (or an empty string) = no, 1 = yes, 2 = unknown. Corresponds to the DBI statement handle
"NULLABLE" attribute.

"cursor_name"
my $cursor_name = $ex->cursor_name;

Returns the name of the cursor associated with the statement handle, if available. Corresponds to the
DBI statement handle "CursorName" attribute.

"param_values"
my $param_values = $ex->param_values;

Returns a reference to a hash containing the values currently bound to placeholders. Corresponds to
the DBI statement handle "ParamValues" attribute.

"statement"
my $statement = $ex->statement;

Returns the statement string passed to the DBI "prepare()" method. Corresponds to the DBI statement
handle "Statement" attribute.

"rows_in_cache"
my $rows_in_cache = $ex->rows_in_cache;

the number of unfetched rows in the cache if the driver supports a local row cache for "SELECT"
statements. Corresponds to the DBI statement handle "RowsInCache" attribute.

Exception::Class::DBI::Unknown
Exceptions of this class are thrown when the context for a DBI error cannot be determined. Inherits from
Exception::Class::DBI, but implements no methods of its own.

Copyright And License

       Copyright (c) 2002-2019, David E. Wheeler. Some Rights Reserved.

       This module is free software; you can redistribute it and/or modify it  under  the  same  terms  as  Perl
       itself.

perl v5.34.0                                       2022-06-30                         Exception::Class::DBI(3pm)

Description

       This module offers a set of DBI-specific exception classes. They inherit from Exception::Class, the base
       class for all exception objects created by the Exception::Class module from the CPAN.
       Exception::Class::DBI itself offers a single class method, "handler()", that returns a code reference
       appropriate for passing to the DBI "HandleError" attribute.

       The exception classes created by Exception::Class::DBI are designed to be thrown in certain DBI contexts;
       the code reference returned by "handler()" and passed to the DBI "HandleError" attribute determines the
       context and throws the appropriate exception.

       Each of the Exception::Class::DBI classes offers a set of object accessor methods in addition to those
       provided by Exception::Class. These can be used to output detailed diagnostic information in the event of
       an exception.

Interface

       Exception::Class::DBI inherits from Exception::Class, and thus its entire interface. Refer to the
       Exception::Class documentation for details.

   ClassMethod
       "handler"
             my $dbh = DBI->connect($data_source, $username, $auth, {
                 PrintError  => 0,
                 RaiseError  => 0,
                 HandleError => Exception::Class::DBI->handler
             });

           This method returns a code reference appropriate for passing to the DBI "HandleError" attribute. When
           DBI  encounters  an  error, it checks its "PrintError", "RaiseError", and "HandleError" attributes to
           decide what to do about it. When "HandleError" has been set to a code  reference,  DBI  executes  it,
           passing  it  the  error string that would be printed for "PrintError", the DBI handle object that was
           executing the method call that triggered the error, and the return value of that method call (usually
           "undef"). Using these arguments, the code reference provided by "handler()" determines what  type  of
           exception  to  throw.  Exception::Class::DBI contains the subclasses detailed below, each relevant to
           the DBI handle that triggered the error.

Name

       Exception::Class::DBI - DBI Exception objects

Note

Note: Not all of the attributes offered by the DBI are exploited by these exception classes. For example,
       the "PrintError" and "RaiseError" attributes seemed redundant. But if  folks  think  it  makes  sense  to
       include  the  missing attributes for the sake of completeness, let me know. Enough interest will motivate
       me to get them in.

Subclassing

       It is possible to subclass Exception::Class::DBI. The trick is to subclass its subclasses,  too.  Similar
       to  subclassing  DBI  itself, this means that the handle subclasses should exist as subnamespaces of your
       base subclass.

       It's easier to explain with an example. Say that you wanted to add a new method  to  all  DBI  exceptions
       that outputs a nicely formatted error message.  You might do it like this:

         package MyApp::Ex::DBI;
         use base 'Exception::Class::DBI';

         sub full_message {
             my $self = shift;
             return $self->SUPER::full_message unless $self->can('statement');
             return $self->SUPER::full_message
                 . ' [for Statement "'
                 . $self->statement . '"]';
         }

       You can then use this subclass just like Exception::Class::DBI itself:

         my $dbh = DBI->connect($dsn, $user, $pass, {
             PrintError  => 0,
             RaiseError  => 0,
             HandleError => MyApp::Ex::DBI->handler,
         });

       And  that's  all  well  and good, except that none of Exception::Class::DBI's own subclasses inherit from
       your class, so most exceptions won't be able to use your spiffy new method.

       The solution is to create subclasses of both the  Exception::Class::DBI  subclasses  and  your  own  base
       subclass, as long as they each use the same package name as your subclass, plus "H", "DRH", "DBH", "STH",
       and "Unknown".  Here's what it looks like:

         package MyApp::Ex::DBI::H;
         use base 'MyApp::Ex::DBI', 'Exception::Class::DBI::H';

         package MyApp::Ex::DBI::DRH;
         use base 'MyApp::Ex::DBI', 'Exception::Class::DBI::DRH';

         package MyApp::Ex::DBI::DBH;
         use base 'MyApp::Ex::DBI', 'Exception::Class::DBI::DBH';

         package MyApp::Ex::DBI::STH;
         use base 'MyApp::Ex::DBI', 'Exception::Class::DBI::STH';

         package MyApp::Ex::DBI::Unknown;
         use base 'MyApp::Ex::DBI', 'Exception::Class::DBI::Unknown';

       And  then  things  should  work just spiffy! Of course, you probably don't need the H subclass unless you
       want to add other methods for the DRH, DBH, and STH classes to inherit from.

Support

       This module is stored in an  open  GitHub  repository  <http://github.com/plicease/Exception-Class-DBI/>.
       Feel free to fork and contribute!

       Please  file bug reports via GitHub Issues <http://github.com/plicease/Exception-Class-DBI/issues/> or by
       sending mail to bug-Exception-Class-DBI@rt.cpan.org <mailto:bug-Exception-Class-DBI@rt.cpan.org>.

Synopsis

         use DBI;
         use Exception::Class::DBI;

         my $dbh = DBI->connect($dsn, $user, $pass, {
             PrintError  => 0,
             RaiseError  => 0,
             HandleError => Exception::Class::DBI->handler,
         });

         eval { $dbh->do($sql) };

         if (my $ex = $@) {
             print STDERR "DBI Exception:\n";
             print STDERR "  Exception Type: ", ref $ex, "\n";
             print STDERR "  Error:          ", $ex->error, "\n";
             print STDERR "  Err:            ", $ex->err, "\n";
             print STDERR "  Errstr:         ", $ex->errstr, "\n";
             print STDERR "  State:          ", $ex->state, "\n";
             print STDERR "  Return Value:   ", ($ex->retval || 'undef'), "\n";
         }

To Do

       •   I need to figure out a non-database specific way of testing STH exceptions.  DBD::ExampleP works well
           for DRH and DBH exceptions, but not so well for STH exceptions.