If you don't want the user to see the nitty-gritty, there's no point in parsing it before showing it to them -- just don't show it at all. Trap the error and make it a generic "Something went wrong" message to the user, and dump the real message to the error log. 
my $errmsg = '';
my $sql = "INSERT INTO url (url, url_id) VALUES (?, ?)";
my @bind = ( 'blah.com', 3 );
$dbh->do($sql,{},@bind);
if( $dbh->err ){
  warn "INSERT url FAILED: " . $dbh->errstr;
  $errmsg = "There was an error adding the URL";
}

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If there's a few known errors, you could check for those to display a different user message: 
if( $dbh->err ){
  warn "INSERT url FAILED: " . $dbh->errstr;
  if( $dbh->err eq '123' ){
    $errmsg = "Please fix ___ before adding the URL.";
  }elsif( $dbh->errstr =~ /not unique/ ){
    $errmsg = "This URL already exists.";
  }else{
    $errmsg = "There was an error adding the URL";
  }
}

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Even better is to try to trap the conditions that create the error .. for example, in this case, a SELECT to see if the "url" column already exists could be done first and if a row is found toss an error to the user. 
my $tmp_id = $dbh->selectrow_array("select url_id from url where url =
+ ?",{},$url);
if( $ct ){
  $errmsg = "The URL '$url' already exists w/id=$tmp_id.";
  return;
}
...
INSERT INTO ...

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One more advantage of using the last two code blocks above is that you have code that's hit IFF a certain error condition arises, so if you check the test coverage it won't be 100% for these blocks unless you have explicit tests for those errors -- so it explicitly outlines the errors in the code, and makes it easier to list the possible run-time conditions to test for.

In reply to Re: Mapping database errors to user errors by davidrw
in thread Mapping database errors to user errors by jplindstrom

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