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[Full documentation index](<https://docs.dhtmlx.com/planning-engine/llms.txt>)


# 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, and its input uses gantt's field names (`start_date`, `duration`, `parent`, `constraint_type`, `auto_scheduling`). 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 Rust records. `plen-core` has no JSON input. For typed JSON input, use the `plen-wire` crate or the `plen` CLI.
- You know each task's effective calendar, as gantt resolves it.
- The example parses dates with `chrono` (`cargo add chrono`).

## Steps

1. Set the scheduling config to gantt's model. Use [`CalendarMode::Task`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/calendar-mode.md>) for task calendars only, or `CalendarMode::TaskInherited` if gantt has `inherit_calendar: true`. Copy gantt's `work_time` into `use_calendars` explicitly. If you leave `use_calendars` out, Planning Engine schedules on calendars:

   ```rust
   use plen_core::{CalendarMode, SchedulingConfig};

   let gantt_work_time = true; // gantt `config.work_time`

   let config = SchedulingConfig {
       calendar_mode: CalendarMode::Task,
       use_calendars: gantt_work_time,
       ..Default::default()
   };
   ```

   Set `root_id` only when gantt's virtual root isn't `0`. The other auto-scheduling options (`apply_constraints`, `gap_behavior`, `move_projects`, `schedule_from_end`, `project_start`, `use_progress`) keep their gantt names.

2. Add one [`CalendarData`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/calendar-data.md>) per calendar your tasks use, and set each task's `calendar_id` 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`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/task-data.md>):
   - gantt `type: "project"` becomes [`TaskType::Summary`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/task-type.md>). A summary takes both `start_date` and `end_date`, or neither. Drop its `duration`, or strict validation rejects the task.
   - A `parent` equal to `root_id` means "no parent". You can copy it as is.
   - A leaf task needs two of `start_date`, `end_date` and `duration`. If you send all three, they must agree.
   - If your gantt event handlers cancel auto-scheduling for a task, set `auto_scheduling: false` on it. The planner never moves it.

4. Map gantt link `type` values `"0"`, `"1"`, `"2"` and `"3"` to [`LinkType::Fs`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/data/link-type.md>), `Ss`, `Ff` and `Sf`. Copy `lag` and leave `lag_unit` as `None`, because gantt measures lag in `config.duration_unit`.

5. Convert each assignment to a slice of its task's work. Don't send gantt's `mode`.
   - `default` and `fixedDuration`: `delay` becomes `offset` and `duration` stays `duration`. Leave both `None` 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`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/project/project.md>) 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.

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

```rust
use chrono::NaiveDateTime;
use plen_core::{
    AssignmentData, CalendarData, CalendarMode, DateTime, Id, LinkData, LinkType, Project,
    ProjectData, ResourceData, SchedulingConfig, SolveOptions, TaskData, TaskType, Worktime,
};

// Records as your server holds them after parsing gantt's JSON.
struct GanttTask {
    id: i32,
    parent: i32,
    kind: &'static str, // gantt `type`
    start_date: &'static str,
    end_date: Option<&'static str>,
    duration: f64,
    calendar_id: &'static str, // effective calendar, already resolved by gantt
}

struct GanttLink {
    id: i32,
    source: i32,
    target: i32,
    kind: &'static str, // gantt `type`: "0".."3"
    lag: f64,
}

struct GanttAssignment {
    id: i32,
    task_id: i32,
    resource_id: &'static str,
    value: f64,
    delay: Option<f64>,    // `default` and `fixedDuration` modes
    duration: Option<f64>, // `default` and `fixedDuration` modes
}

fn date(s: &str) -> Result<DateTime, chrono::ParseError> {
    // Use the format your gantt `date_format` produces.
    Ok(NaiveDateTime::parse_from_str(s, "%Y-%m-%d %H:%M")?.into())
}

fn link_type(kind: &str) -> Option<LinkType> {
    match kind {
        "0" => Some(LinkType::Fs),
        "1" => Some(LinkType::Ss),
        "2" => Some(LinkType::Ff),
        "3" => Some(LinkType::Sf),
        _ => None,
    }
}

fn task(g: &GanttTask) -> Result<TaskData, chrono::ParseError> {
    let mut t = TaskData::new(g.id);
    t.parent = Some(Id::from(g.parent)); // gantt's root (0) becomes "no parent"
    t.start_date = Some(date(g.start_date)?);
    t.calendar_id = Some(g.calendar_id.into());
    match g.kind {
        "project" => {
            // A summary takes both dates or neither, never a duration.
            t.task_type = TaskType::Summary;
            t.end_date = g.end_date.map(date).transpose()?;
            if t.end_date.is_none() {
                t.start_date = None;
            }
        }
        "milestone" => {
            t.task_type = TaskType::Milestone;
            t.duration = Some(0.0);
        }
        _ => t.duration = Some(g.duration),
    }
    Ok(t)
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let gantt_tasks = [
        GanttTask { id: 1, parent: 0, kind: "project", start_date: "2026-03-02 00:00", end_date: Some("2026-03-07 00:00"), duration: 5.0, calendar_id: "global" },
        GanttTask { id: 2, parent: 1, kind: "task", start_date: "2026-03-02 00:00", end_date: None, duration: 3.0, calendar_id: "global" },
        GanttTask { id: 3, parent: 1, kind: "task", start_date: "2026-03-02 00:00", end_date: None, duration: 4.0, calendar_id: "part-time" },
        GanttTask { id: 4, parent: 0, kind: "milestone", start_date: "2026-03-02 00:00", end_date: None, duration: 0.0, calendar_id: "global" },
    ];
    let gantt_links = [
        GanttLink { id: 1, source: 2, target: 3, kind: "0", lag: 0.0 },
        GanttLink { id: 2, source: 1, target: 4, kind: "0", lag: 0.0 },
    ];
    let gantt_assignments = [GanttAssignment {
        id: 1, task_id: 3, resource_id: "dev", value: 1.0, delay: Some(1.0), duration: Some(2.0),
    }];

    let config = SchedulingConfig {
        calendar_mode: CalendarMode::Task, // gantt's calendar model
        use_calendars: true,               // gantt `config.work_time`
        ..Default::default()
    };

    let calendars = vec![
        CalendarData { id: "global".into(), worktime: None },
        CalendarData {
            id: "part-time".into(),
            worktime: Some(Worktime {
                days: Some([false, true, true, true, true, false, false]), // Mon-Thu
                ..Default::default()
            }),
        },
    ];

    let tasks = gantt_tasks.iter().map(task).collect::<Result<Vec<_>, _>>()?;

    let mut links = Vec::new();
    for g in &gantt_links {
        links.push(LinkData {
            id: g.id.into(),
            source: g.source.into(),
            target: g.target.into(),
            link_type: link_type(g.kind).ok_or("unknown link type")?,
            lag: g.lag,
            lag_unit: None,
        });
    }

    let assignments = gantt_assignments
        .iter()
        .map(|g| AssignmentData {
            id: Some(g.id.into()),
            task: g.task_id.into(),
            resource: g.resource_id.into(),
            value: g.value,
            offset: g.delay,
            duration: g.duration,
        })
        .collect();

    let data = ProjectData {
        config,
        calendars,
        tasks,
        links,
        resources: vec![ResourceData { id: "dev".into(), capacity: None, calendar_id: None }],
        assignments,
    };

    let mut project = Project::default();
    let result = project.solve(Some(data), &SolveOptions::default())?;

    for m in &result.updates {
        // Only changed fields are set. Summaries are included: write them back too.
        if let Some(start) = m.start_date {
            println!("{} start_date = {}", m.id, start);
        }
        if let Some(end) = m.end_date {
            println!("{} end_date = {}", m.id, end);
        }
    }
    Ok(())
}
```

## Keep gantt's triggers on your side

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

- Call [`apply`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/project/project.md#apply>) and then [`solve(None, ...)`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/project/project.md#solve>) wherever gantt would run auto-scheduling: after the user adds a link, drags a task, or saves the lightbox. See [Data Updates](<https://docs.dhtmlx.com/planning-engine/rust/live-projects/editing-a-project.md>).
- `gantt.autoSchedule(id, inclusive)` is [`SolveOptions::subtree`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/project/solve-options.md#subtree>). See [Reschedule a branch](<https://docs.dhtmlx.com/planning-engine/rust/how-to/reschedule-a-branch.md>).
- 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(Some(data), ...)`.
- gantt core rewrites descendant dates when inherited calendars or effort change. Forward those date and duration edits as ordinary [`TaskUpdate`](<https://docs.dhtmlx.com/planning-engine/rust/api/core/changes/task-update.md>) 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 `constraint_date`, 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](<https://docs.dhtmlx.com/planning-engine/rust/how-to/accept-messy-input.md>).
- `week`, `month` and `year` duration units and calendars with `customWeeks` are rejected. A gantt merged calendar can contain `customWeeks`, so such projects can't be imported yet.
- Dates are naive local date-times with no timezone and no DST. gantt's JS engine uses the host time zone, so its arithmetic follows DST. Convert dates to naive 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 `project_constraint: true`, children inherit the parent's constraint. gantt's engine ignores it. With `use_progress`, a completed child of a moving summary stays in place. gantt drags it along. With `descendant_links: true` in block mode, gantt fails with a cycle error and Planning Engine schedules the project. See [Links, constraints and summaries](<https://docs.dhtmlx.com/planning-engine/rust/scheduling/links-constraints-summaries.md>).
- 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 call can panic. See [Error handling](<https://docs.dhtmlx.com/planning-engine/rust/error-handling.md>).

## Result

The example prints the changed fields:

```text
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](<https://docs.dhtmlx.com/planning-engine/rust/how-to/load-all-task-dates.md>).