flowable/flowable-engine · error · ActivitiException

Cannot assign a groupId to a task assignment that already…

Error message

Cannot assign a groupId to a task assignment that already has a userId

What it means

Consistency guard in flowable5 IdentityLinkEntity.setGroupId: the identity link already has a userId set, and assigning a groupId as well would make the link ambiguous (both a user and a group). The entity enforces mutual exclusivity of userId and groupId.

Solutions

1. Create a separate identity link for the group; use taskService.addCandidateGroup / addGroupIdentityLink.
2. Null out userId first only if you truly intend to convert the link.
3. Map external 'assignee OR group' inputs to two distinct API calls.

Example fix

// before
link.setUserId("kermit"); link.setGroupId("management"); // throws

// after
taskService.setAssignee(taskId, "kermit");
taskService.addCandidateGroup(taskId, "management");

if (link.getUserId() != null && groupId != null) {
    throw new IllegalArgumentException("cannot assign group to user-based link");
}

function isGroupLinkAssignable(link) {
  return link.getUserId() == null;
}

try {
    taskService.addCandidateGroup(taskId, groupId);
} catch (ActivitiException e) {
    log.warn("Link conflict on task {}: {}", taskId, e.getMessage());
}

When it happens

Trigger: Calling setGroupId on an IdentityLinkEntity whose userId is already non-null; assignment code that sets assignee first and then tries to add a group on the same entity.

Common situations: Custom task assignment listeners combining assignee and candidate group in one entity; converters that map 'assignee or group' fields from external systems onto a single link; reuse of entity instances across task assignments.

Related errors

• Cannot assign a userId to a task assignment that already…
• Cannot assign a groupId to a task assignment that already…
• Cannot assign a userId to a task assignment that already…
• identityId is null
• task not found

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/c6c2b7cf524f249b. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable5-engine/src/main/java/org/activiti/engine/impl/persistence/entity/IdentityLinkEntity.java:149

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        if (this.groupId != null && userId != null) {
            throw new ActivitiException("Cannot assign a userId to a task assignment that already has a groupId");
        }
        this.userId = userId;
    }

    @Override
    public String getGroupId() {
        return groupId;
    }

    public void setGroupId(String groupId) {
        if (this.userId != null && groupId != null) {
            throw new ActivitiException("Cannot assign a groupId to a task assignment that already has a userId");
        }
        this.groupId = groupId;
    }

    @Override
    public String getTaskId() {
        return taskId;
    }

    public void setTaskId(String taskId) {
        this.taskId = taskId;
    }

    @Override
    public String getProcessInstanceId() {
        return processInstanceId;
    }

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