You could make your key pair (item+name, user+id) a parameter of a generic 'get' subroutine, but you would still have to figure out how to compare the values associated with the second key. You would also have to make sure that your $this object is initialized with all the possible keys (item, user) so that you can detect typos (and same for $user, $item objects). Something like this to get you started:

sub get_by_string {
   my ($this, $field, $property, $value) = @_;
   die "Invalid field $field" if (!exists $this->{$field});
   return grep { $_->{$property} eq $value } @{$this->{$field}};
}

sub get_by_number {
   my ($this, $field, $property, $value) = @_;
   die "Invalid field $field" if (!exists $this->{$field});
   return grep { $_->{$property} == $value } @{$this->{$field}};
}
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Your get calls would then look like this:

my @items = $obj->get_by_string('item','name',$name);
my @users = $obj->get_by_number('user','id',$id);
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