SL::DB::Helper::Util: verschiedene RDBO-Hilfsfunktionen; Anfang: is_unique

diff --git a/SL/DB/Helper/Util.pm b/SL/DB/Helper/Util.pm
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+package SL::DB::Helper::Util;
+
+use strict;
+
+use Rose::DB::Object::Util;
+
+use parent qw(Exporter);
+our @EXPORT_OK = qw(is_unique);
+
+#
+# Public functions not exported by default
+#
+
+sub is_unique {
+  my ($self, @columns) = @_;
+
+  my @filter =  map { ($_ => $self->$_) } @columns;
+  if (Rose::DB::Object::Util::is_in_db($self)) {
+    push @filter, map { ("!${_}" => $self->$_ )} $self->meta->primary_key;
+  }
+
+  return !$self->_get_manager_class->get_first(where => [ and => \@filter ]);
+}
+
+1;
+
+__END__
+
+=pod
+
+=encoding utf8
+
+=head1 NAME
+
+SL::DB::Helper::Util - Helper functions for Rose::DB::Object instances
+
+=head1 SYNOPSIS
+
+  package SL::DB::AuthUser;
+
+  use SL::DB::Helper::Util;
+
+  sub validate {
+    ...
+    if (!SL::DB::Helper::Util::is_unique($self, 'login')) {
+      push @errors, "Login not unique";
+    }
+  }
+
+=head1 OVERVIEW
+
+This is a collection of assorted helper and utility functions for
+Rose::DB::Object instances that don't require full-blown mixin helpers
+like L<SL::DB::ActsAsList>. The module does not export any function by
+default, but all of the public ones can be requested in the usual
+way.
+
+Each function can be called either as fully qualified name with the
+object instance as the first argument or (if the function is imported)
+as an intance method on the object instance.
+
+=head1 FUNCTIONS
+
+=over 4
+
+=item C<is_unique @columns>
+
+Returns trueish if C<$self> is unique in its table regarding the
+columns C<@columns>. What it does is look for existing records in the
+database whose stored column values match C<$self>'s current values
+for these columns. If C<$self> already exists in the database then
+that row is not considered during the search.
+
+=back
+
+=head1 BUGS
+
+Nothing here yet.
+
+=head1 AUTHOR
+
+Moritz Bunkus E<lt>m.bunkus@linet-services.deE<gt>
+
+=cut