Split assignment work#

Hand one task's work to several people, for example one developer for the first two days and another for the rest, without changing the task's dates.

The offset and duration fields of AssignmentData do this. Each assignment books only its own part of the task, called a slice. For how slices affect load, see Resources and assignments.

Steps#

1. Book each person on their part of the task. Both fields are Double and count worked time from the task start, in the task's durationUnit:

   • offset: where the slice starts. null means the task start.
   • duration: how much work the slice books. null means up to the task end.
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   // Anna works the first 2 days of `build`.
   var anna = new AssignmentData()
       .withId(Id.str("build:anna"))
       .withTask(Id.str("build"))
       .withResource(Id.str("anna"))
       .withValue(1.0)
       .withDuration(2.0);
   // Ben starts after 2 days of work and finishes the task.
   var ben = new AssignmentData()
       .withId(Id.str("build:ben"))
       .withTask(Id.str("build"))
       .withResource(Id.str("ben"))
       .withValue(1.0)
       .withOffset(2.0);
   

2. Pass the assignments to solve(data, options) as usual. Then check the booked load with Project#loadProfile:

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   var query = new ProfileQuery(from, to);
   query.basis = Basis.DAY;
   LoadProfile profile = project.loadProfile(new LoadProfileOptions(query));
   

3. To move the handover in a live project, send an AssignmentUpdate for each slice, then call solve(null, options):

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   var changes = new SchedulingChanges();
   changes.assignments.update.add(
       new AssignmentUpdate(Id.str("build:anna")).withDuration(Patch.of(3.0)));
   changes.assignments.update.add(
       new AssignmentUpdate(Id.str("build:ben")).withOffset(Patch.of(3.0)));
   

4. To book the whole task again, set the field to Patch.nullValue(). A cleared offset goes back to the task start. A cleared duration runs up to the task end.

The full example splits the 4-day build task between Anna and Ben, prints their daily load, then moves the handover one day later:

import java.util.ArrayList;
import java.util.List;
import org.dhtmlx.plen.*;

public class SplitAssignmentWork {
  static AssignmentData slice(String resource, Double offset, Double duration) {
    return new AssignmentData()
        .withId(Id.str("build:" + resource))
        .withTask(Id.str("build"))
        .withResource(Id.str(resource))
        .withValue(1.0)
        .withOffset(offset)
        .withDuration(duration);
  }

  static void printLoad(Project project) {
    // Daily load from Monday 2026-08-10 to Friday 2026-08-14.
    var query = new ProfileQuery(
        Moment.fromYmdHm(2026, 8, 10, 0, 0), Moment.fromYmdHm(2026, 8, 15, 0, 0));
    query.basis = Basis.DAY;
    LoadProfile profile = project.loadProfile(new LoadProfileOptions(query));
    for (ResourceLoad resource : profile.resources) {
      var loads = new ArrayList<Double>();
      for (LoadBucket bucket : resource.buckets) loads.add(bucket.load);
      System.out.println("  " + resource.resource + ": " + loads);
    }
  }

  public static void main(String[] args) throws Exception {
    // `build`: 4 working days, Monday to Thursday.
    var build = new TaskData(Id.str("build"))
        .withStartDate(Moment.fromYmdHm(2026, 8, 10, 8, 0))
        .withDuration(4.0);

    var data = new ProjectData()
        .withTasks(List.of(build))
        .withResources(List.of(
            new ResourceData().withId(Id.str("anna")),
            new ResourceData().withId(Id.str("ben"))))
        .withAssignments(List.of(
            // Anna works the first 2 days of `build`.
            slice("anna", null, 2.0),
            // Ben starts after 2 days of work and finishes the task.
            slice("ben", 2.0, null)));

    var project = new Project();
    ScheduleResult first = project.solve(data, new SolveOptions());
    System.out.println("handover after day 2");
    printLoad(project);

    // Move the handover one day later: Anna works 3 days, Ben the last one.
    var changes = new SchedulingChanges().withBaselineId(first.baselineId);
    changes.assignments.update.add(
        new AssignmentUpdate(Id.str("build:anna")).withDuration(Patch.of(3.0)));
    changes.assignments.update.add(
        new AssignmentUpdate(Id.str("build:ben")).withOffset(Patch.of(3.0)));

    ApplyReport report = project.apply(changes);
    if (!report.rejected.isEmpty()) {
      throw new IllegalStateException("rejected: " + report.rejected);
    }
    ScheduleResult result = project.solve(null, new SolveOptions());
    System.out.println("handover after day 3, moved tasks: " + result.updates.size());
    printLoad(project);
  }
}

loadProfile needs a solved project, so call solve(null, options) after apply and before you read the load again.

Things to check#

• Slices never move tasks. A slice edit leaves every task date as it was, but it changes the baselineId. A SchedulingChanges that still carries the old token fails with a ProjectException whose code is STALE_BASELINE.
• The engine clips the slice to the task's work when it books load. A slice that runs past the task end books only up to the end. An offset at or past the task's duration books nothing. If the task gets shorter later, the slice follows it.
• Non-working time and leveling pauses don't count as worked time. A pause or a levelingDelay moves the slice together with the work.
• Two slices of the same resource on the same task add up where they overlap.
• Strict validation rejects an offset below 0 or not finite, and a duration of 0 or less or not finite. solve(data, options) throws an InputException with path set to assignments[i].offset or assignments[i].duration. In apply, the same values show up as rejected operations in ApplyReport.rejected, at paths like assignments.update[0]. See Recover from rejected changes.
• With Validation.REPAIR, the engine clears an invalid value and adds a Note.Repaired, so the assignment books the whole task. See Accept messy input.
• An assignment on an unscheduled task keeps its slice and books it again when the task is scheduled.

Result#

The example prints each person's load for Monday to Friday, before and after the handover moves:

handover after day 2
  anna: [1.0, 1.0, 0.0, 0.0, 0.0]
  ben: [0.0, 0.0, 1.0, 1.0, 0.0]
handover after day 3, moved tasks: 0
  anna: [1.0, 1.0, 1.0, 0.0, 0.0]
  ben: [0.0, 0.0, 0.0, 1.0, 0.0]

The load moves from Ben to Anna on Wednesday. build keeps its dates, so solve(null, options) reports no moved tasks.