Perl Dbi Error
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login Username: * Password: * Create new accountRequest new password Home » DBI: handling database errors ( categories: databases ) Basically, there are two ways of perl dbi execute return value handling database errors, check (almost) every DBI call for errors or set 'RaiseError' perl dbi handleerror attribute to '1ยด: -- Manual checking This way, you have to add code yourself to check for database error conditions, so perl dbi connect error handling after nearly every method call you should check if the operation completed successfully. There are two DBI methods that are very helpful to manually check for database errors: 'err' and 'errstr'. 'err' returns the native
Perl Dbi Errstr
database engine error code from the last DBI method called. The code returned is usually an integer. 'errstr' returns the native database engine error message from the last DBI method called. Example: $dbh = DBI->connect($data_src, $user, $pwd) or die $DBI::errstr;
my $sth = $dbh->prepare("DELETE FROM table WHERE count < '?'");
$sth->execute(25);
if ( $sth->err )
{
die "ERROR! return code: . $sth->err . perl dbi try catch " error msg: " . $sth->errstr . "\n";
}
-- Setting 'RaiseError' attribute If DBI 'RaiseError' attribute is set to '1' (is '0' by default), then any database error will cause the DBI module to 'die' with an appropriate message. When using 'RaiseError', is recommended to set the 'PrintError' atribute to '0') Example: my $dbh = DBI->connect($dsn, $user, $pw, { RaiseError => 1, PrintError => 0 });
Bookmark/Search this post with: | | | | » login or register to post comments You can also provide a Submitted by Kelicula on Wed, 04/15/2009 - 00:58. You can also provide a custom sub to handle errors with the RaiseError flag set. After establishing server connection: $dbh->{HandleError} = sub { my $error = shift; # do something with error...; }; Or in attributes: my $dbh = DBI->connect("DBI:......, { RaiseError => 1, HandleError => \&DBerror })|| die $DBI::errstr; sub DBerror { my $error = shift; # do something with error... } etc... Only disadvantage is knowing what line the error originated from in your script. -------- I'm unique just like everyone else! » login or register to post comments Home | Links | RSS feed | Forums Copyright © 2006 Toshiro Viera Stalker - All rights reserved
Go to comments The DBI module lets you handle errors yourself if you don't like its built-in behavior. DBI lets you handle the errors dbi error fatal at either the database or the statement handle level by specifying attributes:
Try Catch In Perl
my $dbh = DBI->connect( ..., ..., \%attr ); my $sth = $dbh->prepare( ..., \%attr ); There are several attributes
Dbi Err Fatal
that affect error handling, each of which you can use with either a connection or a statement handle: Attribute Type Default PrintWarn Boolean On PrintError Boolean On RaiseError Boolean Off HandleError Code http://www.perlhowto.com/dbi_handling_database_errors Ref Off ShowErrorStatement Boolean Off These attributes are inherited by anything derived from the handle where you set them. The PrintWarn and PrintError attributes do just what they say. They are on by default, and they don't stop your program. In this example, you prepare a statement that expects one bind parameter, but when you execute it, you give two parameters instead: use DBI; https://www.effectiveperlprogramming.com/2010/07/set-custom-dbi-error-handlers/ my $dbh = DBI->connect( 'dbi:SQLite:dbname=test.db', '', '', {} ); my $sth = $dbh->prepare( 'SELECT * FROM Cats WHERE id = ?' ); $sth->execute( 1, 2 ); while( my @row = $sth->fetchrow_array ) { print "row: @row\n"; } print "Got to the end\n"; Since PrintError is true by default, DBI prints the error, but it allows the program to continue even though there was an error: DBD::SQLite::st execute failed: called with 2 bind variables when 1 are needed at dbi-test.pl line 12. Got to the end If you set the ShowErrorStatement attribute, you get a better error message because DBI appends the SQL statement that you tried to execute. You can set this either database handle or the statement handle, but if you don't know which statement is causing the problem, it's easier to set it as part of the database handle: # The rest of the program is the same my $dbh = DBI->connect( 'dbi:SQLite:dbname=test.db', '', '', { ShowErrorStatement => 1, } ); The error message shows the SQL statement, but the program still continues: DBD::SQLite::st execute failed: called with 2 bind variables when 1 are needed [for Statemen
RecentThreads NewestNodes Donate What'sNew on Apr 14, 2000 at 03:36UTC ( #7568=perltutorial: print w/replies, xml ) Need Help?? Tricks with DBI 1. Check for database errors. You're going to run into errors with databases for similar reasons that you do http://www.perlmonks.org/?node_id=7568 when using system calls and the like. And just as you should always http://www.perl.com/pub/1999/10/DBI.html check the return code of your system calls, so should you always check the return status of your database calls. The easiest way to do this is by setting DBI's RaiseError attribute to 1; first connect to the database (and check the return), then set the RaiseError attribute: my $dbh = perl dbi DBI->connect('foo', 'bar', 'baz', 'mysql') or die "Can't connect: ", $DBI::errstr; $dbh->{RaiseError} = 1; [download] By doing this, you ensure that any database error will cause a die. Why is this good? Because generally, if you're writing a database application and you have a database error, you don't want to continue as if nothing happened. :) (Besides, you can always catch the die in an eval; perl dbi error just make sure that you handle the errors rather than ignoring them.) The other way to check for errors, of course, is to check the return of each method call, eg.: my $sth = $dbh->prepare("select id from foo") or die "Can't prepare: ", $dbh->errstr; $sth->execute or die "Can't execute: ", $dbh->errstr; [download] So as not to make your code one big C-like mess of error checking, though, you might as well just use RaiseError. 2. Use placeholders instead of literal values. This is covered pretty thoroughly in What are placeholders in DBI. Suffice it to say here, then, that you should use placeholders instead of literal values. Always (or pretty much, at least). And, for the same reasons, you should use prepare_cached instead of prepare. 3. The fastest way to fetch. When you execute a SELECT statement, you want to get the data back as quickly as possible. The fastest way to do this is to use the bind_columns and fetch methods, because they don't copy a bunch of memory around. bind_columns binds Perl variables to columns returned from your SELECT statement. For example, if you had the following SQL statemen
databases started to get to be a big deal in the 1970's, andthey're still a big deal today, which is a little peculiar, because they're a 1960's technology. A relational database is a bunch of rectangular tables. Each row of a table is a record about one person or thing; the record contains several pieces of information called fields. Here is an example table: LASTNAME FIRSTNAME ID POSTAL_CODE AGE SEX Gauss Karl 119 19107 30 M Smith Mark 3 T2V 3V4 53 M Noether Emmy 118 19107 31 F Smith Jeff 28 K2G 5J9 19 M Hamilton William 247 10139 2 M The names of the fields are LASTNAME, FIRSTNAME, ID, POSTAL_CODE, AGE, and SEX. Each line in the table is a record, or sometimes a row or tuple. For example, the first row of the table represents a 30-year-old male whose name is Karl Gauss, who lives at postal code 19107, and whose ID number is 119. Sometimes this is a very silly way to store information. When the information naturally has a tabular structure it's fine. When it doesn't, you have to squeeze it into a table, and some of the techniques for doing that are more successful than others. Nevertheless, tables are simple and are easy to understand, and most of the high-performance database systems you can buy today operate under this 1960's model. About SQL SQL stands for Structured Query Language. It was invented at IBM in the 1970's. It's a language for describing searches and modifications to a relational database. SQL was a huge success, probably because it's incredibly simple and anyone can pick it up in ten minutes. As a result, all the important database systems support it in some fashion or another. This includes the big players, like Oracle and Sybase, high-quality free or inexpensive database systems like MySQL, and funny hacks like Perl's DBD::CSV module, which we'll see later. There are four important things one can do with a table: SELECT Find all the records that have a certain property
INSERT Add new records DELETE Remove old records UPDATE Modify records that are already there Those are the four most important SQL commands, also called queries. Suppose that the example table above is named people. Here are examples of each of the four important kinds of queries: SELECT firstname FROM people WHERE lastname = 'Smith' (Locate the first names of all the Smiths.) DELETE FROM people WHERE id = 3 (Delete Mark Smith from the table) UPDATE people SET age = age+1 WHERE id = 247 (William Hamilton just had a birthday.) INSERT INTO people VALUES ('Euler', 'Leonhard', 248, NULL, 58, 'M') (Add Leonhard Euler to the table.) There are a bunch of other SQL commands for creating and discarding tab