DHTMLX Planning Engine Documentation

Import from dhtmlxGantt#

Load a dhtmlxGantt project into Planning Engine and get the same task dates the gantt auto-scheduler would give you.

Planning Engine's scheduling step is a port of the dhtmlxGantt v2 auto-scheduling engine. Its records use gantt's fields under PascalCase names (StartDate, Duration, Parent, ConstraintType, AutoScheduling), so most of the import copies fields one to one. The steps below cover the places where a straight copy gives different dates or fails validation.

Prerequisites#

  • Your gantt tasks, links, resources and assignments are parsed into your own C# records. Plen.Core has no JSON input. To read gantt-style JSON directly, use the separate Plen.Wire package. See Exchange JSON with a client.
  • You know each task's effective calendar, as gantt resolves it.

Steps#

  1. Set the scheduling config to gantt's model. Use CalendarMode.Task for task calendars only, or CalendarMode.TaskInherited if gantt has inherit_calendar: true. Copy gantt's work_time into UseCalendars explicitly. If you leave UseCalendars unset, it stays true and Planning Engine schedules on calendars:

    var ganttWorkTime = true; // gantt `config.work_time`

var data = new ProjectData
{
    Config =
    {
        CalendarMode = CalendarMode.Task,
        UseCalendars = ganttWorkTime,
    },
};

    Set RootId only when gantt's virtual root isn't 0. The other auto-scheduling options (ApplyConstraints, GapBehavior, MoveProjects, ScheduleFromEnd, ProjectStart, UseProgress) are gantt's options under PascalCase names.

  2. Add one CalendarData per calendar your tasks use, and set each task's CalendarId to its effective calendar. gantt picks that calendar in its adapter: the task's own, else its resource's, else a calendar merged from all its resources, else the parent's. Send the result, not the rules. A merged resource calendar goes in once, under its synthetic id. Don't repeat gantt's precedence or merging in your import code.

  3. Map each task to a TaskData:

    • gantt type: "project" becomes TaskType.Summary. A summary takes both StartDate and EndDate, or neither. Drop its Duration, or strict validation rejects the task.
    • A Parent equal to RootId means "no parent". You can copy it as is.
    • A leaf task needs two of StartDate, EndDate and Duration. If you set all three, they must agree.
    • If your gantt event handlers cancel auto-scheduling for a task, set AutoScheduling = false on it. The planner never moves it.

  4. Map gantt link type values "0", "1", "2" and "3" to LinkType.Fs, Ss, Ff and Sf. Copy lag and leave LagUnit as null, because gantt measures lag in config.duration_unit.

  5. Convert each assignment to a slice of its task's work in AssignmentData. gantt's mode has no counterpart, so don't carry it over.

    • default and fixedDuration: delay becomes Offset and duration stays Duration. Leave both null to book the whole task.
    • fixedDates: set Offset and Duration to the worked time its dates cover, measured from the task start.

    A slice ends at the task end. gantt's fixedDuration can run past it.

  6. Solve the data with Project.Solve and write the changed fields from result.Updates back into gantt. The updates include summaries, which the gantt JS adapter leaves to gantt core. Apply those too, or your summary spans go stale.

This example imports a summary with two tasks, a milestone, two links, a part-time calendar and one default-mode assignment:

using System.Globalization;
using Plen;

GanttTask[] ganttTasks =
[
    new(1, 0, "project", "2026-03-02 00:00", "2026-03-07 00:00", 5, "global"),
    new(2, 1, "task", "2026-03-02 00:00", null, 3, "global"),
    new(3, 1, "task", "2026-03-02 00:00", null, 4, "part-time"),
    new(4, 0, "milestone", "2026-03-02 00:00", null, 0, "global"),
];
GanttLink[] ganttLinks =
[
    new(1, 2, 3, "0", 0),
    new(2, 1, 4, "0", 0),
];
GanttAssignment[] ganttAssignments =
[
    new(1, 3, "dev", 1.0, Delay: 1, Duration: 2),
];

var data = new ProjectData
{
    Config =
    {
        CalendarMode = CalendarMode.Task, // gantt's calendar model
        UseCalendars = true,              // gantt `config.work_time`
    },
    Calendars =
    [
        new CalendarData { Id = "global" },
        new CalendarData
        {
            Id = "part-time",
            Worktime = new Worktime { Days = [false, true, true, true, true, false, false] }, // Mon-Thu
        },
    ],
    Tasks = ganttTasks.Select(ToTask).ToList(),
    Links = ganttLinks.Select(g => new LinkData
    {
        Id = g.Id,
        Source = g.Source,
        Target = g.Target,
        LinkType = ToLinkType(g.Type),
        Lag = g.Lag, // LagUnit stays null: gantt lag is in config.duration_unit
    }).ToList(),
    Resources = [new ResourceData { Id = "dev" }],
    Assignments = ganttAssignments.Select(g => new AssignmentData
    {
        Id = g.Id,
        Task = g.TaskId,
        Resource = g.ResourceId,
        Value = g.Value,
        Offset = g.Delay,
        Duration = g.Duration,
    }).ToList(),
};

var project = new Project();
var result = project.Solve(data, new SolveOptions());

foreach (var m in result.Updates)
{
    // Only changed fields are set. Summaries are included: write them back too.
    if (m.StartDate is { } start) Console.WriteLine($"{m.Id} start_date = {start}");
    if (m.EndDate is { } end) Console.WriteLine($"{m.Id} end_date = {end}");
}

static Moment ParseDate(string s) =>
    // Use the format your gantt `date_format` produces.
    Moment.FromDateTime(DateTime.ParseExact(s, "yyyy-MM-dd HH:mm", CultureInfo.InvariantCulture));

static LinkType ToLinkType(string type) => type switch
{
    "0" => LinkType.Fs,
    "1" => LinkType.Ss,
    "2" => LinkType.Ff,
    "3" => LinkType.Sf,
    _ => throw new ArgumentException($"unknown gantt link type {type}"),
};

static TaskData ToTask(GanttTask g)
{
    var t = new TaskData(g.Id)
    {
        Parent = g.Parent, // gantt's root (0) means "no parent"
        StartDate = ParseDate(g.StartDate),
        CalendarId = g.CalendarId,
    };
    switch (g.Type)
    {
        case "project":
            // A summary takes both dates or neither, never a duration.
            t.TaskType = TaskType.Summary;
            if (g.EndDate is null) t.StartDate = null;
            else t.EndDate = ParseDate(g.EndDate);
            break;
        case "milestone":
            t.TaskType = TaskType.Milestone;
            t.Duration = 0;
            break;
        default:
            t.Duration = g.Duration;
            break;
    }
    return t;
}

// Records as your server holds them after parsing gantt's JSON.
record GanttTask(int Id, int Parent, string Type, string StartDate, string? EndDate, double Duration, string CalendarId);
record GanttLink(int Id, int Source, int Target, string Type, double Lag);
record GanttAssignment(int Id, int TaskId, string ResourceId, double Value, double? Delay, double? Duration);

Keep gantt's triggers on your side#

Planning Engine has no UI triggers and no events. Your code decides when to schedule.

  • Call Project.Apply and then Solve(null, …) wherever gantt would run auto-scheduling: after the user adds a link, drags a task, or saves the lightbox. See Editing a project.
  • gantt.autoSchedule(id, inclusive) is SolveOptions.Subtree. See Reschedule a branch.
  • Change sets can't add or edit calendars. If an assignment change gives a task a new merged calendar, send the whole project again with Solve(data, …).
  • gantt core rewrites descendant dates when inherited calendars or effort change. Forward those date and duration edits as ordinary TaskUpdate changes. Planning Engine doesn't recreate gantt's effort rules.

Differences to expect#

  • Strict validation rejects input that gantt coerces: duplicate ids, a dated constraint with no ConstraintDate, a leaf task with fewer than two of start, end and duration, a dateless summary with no dated children. To get gantt's coercions with a report of each fix, see Accept messy input.
  • TimeUnit has no week, month or year, and calendars with customWeeks can't be represented. A gantt merged calendar can contain customWeeks, so such projects can't be imported yet.
  • Moment is a naive local date-time with no timezone and no DST. gantt's JS engine uses the host time zone, so its arithmetic follows DST. Moment.FromDateTime reads the date and time fields as they are and ignores DateTime.Kind, so convert UTC values to local time before you build the data.
  • result.Notes lists the links, tasks and assignments the engine dropped. gantt drops them silently.
  • Three cases give different dates on purpose. With ProjectConstraint = true, children inherit the parent's constraint. gantt's engine ignores it. With UseProgress, a completed child of a moving summary stays in place. gantt drags it along. With DescendantLinks = true in block mode, gantt fails with a cycle error and Planning Engine schedules the project. See Links, constraints and summaries.
  • Summary-to-summary links in block mode, combined with leaf links between the same summaries, can give different dates. On very large generated graphs the dates drift out of range and the call throws InvalidOperationException. See Error handling.

Result#

The example prints the changed fields:

3 start_date = 2026-03-05 00:00
3 end_date = 2026-03-12 00:00
1 end_date = 2026-03-12 00:00
4 start_date = 2026-03-12 00:00
4 end_date = 2026-03-12 00:00

Task 3 starts when task 2 finishes and works Monday to Thursday only, so it ends a week later. The summary 1 grows to cover it. Task 2 didn't move, so it isn't listed. To get every date on the first load, see Load all task dates.