Modify addUserMultipleProblems of lib/WeBWorK/DB.pm to use

   eval { $self->{problem_user}->insert_records([@problemList]); };
so that a single DB call makes all the inserts.
Test that no records for this user and set exist before making
that call.

lib/WeBWorK/DB.pm

@@ -2057,8 +2057,10 @@ sub addUserMultipleProblems {
 	my ($self, @problemList) = @_;
 
 	my $firstUserProblem = $problemList[0];
+	my $user_id          = $firstUserProblem->user_id;
+	my $set_id           = $firstUserProblem->set_id;
 
-	my ($nv_set_id, $versionNum) = grok_vsetID($firstUserProblem->set_id);
+	my ($nv_set_id, $versionNum) = grok_vsetID($set_id);
 	croak "addUserMultipleProblems does not support versioned sets"
 		if defined($versionNum);
 
@@ -2068,32 +2070,19 @@ sub addUserMultipleProblems {
 	my @tmp = ($firstUserProblem);
 	$self->checkArgs(\@tmp, qw/VREC:problem_user/);
 
-	# Just needed once
-	croak 'addMultipleUserProblems: user set ', $firstUserProblem->set_id, ' for user ', $firstUserProblem->user_id,
-		' not found'
-		unless $self->{set_user}->exists($firstUserProblem->user_id, $firstUserProblem->set_id);
+	croak "addMultipleUserProblems: user set $set_id for user $user_id not found"
+		unless $self->{set_user}->exists($user_id, $set_id);
 
-	my @sawRecordExists;
-	my @otherErrors;
+	# Test whether there are already problem records for this user in this set, as in that case
+	# inserting multiple records at once would trigger an error.
+	my $where = [ user_id_eq_set_id_eq => $user_id, $set_id ];
 
-	for my $userProblem (@problemList) {
-		eval { $self->{problem_user}->add($userProblem); };
-		if (my $ex = caught WeBWorK::DB::Ex::RecordExists) {
-			push(@sawRecordExists, $userProblem->problem_id);
-		} elsif ($@) {
-			push(@otherErrors, "for problem_id $userProblem->problem_id) saw error: $@\n");
-		}
-	}
-	if (@sawRecordExists || @otherErrors) {
-		croak join(
-			'',
-			@sawRecordExists
-			? join('',
-				'addUserMultipleProblems: the following user problems existed before ',
-				join(', ', @sawRecordExists), "\n")
-			: '',
-			@otherErrors
-		);
+	croak "addMultipleUserProblems cannot be run as set $set_id already contains some problems for user $user_id"
+		if $self->{problem_user}->count_where($where);
+
+	eval { $self->{problem_user}->insert_records([@problemList]); };
+	if ($@) {
+		croak "addUserMultipleProblems: $@";
 	}
 }