Dragging tasks within the end date of source task DHTMLX Gantt

Question

i customize a DHTMLX gantt with my db. For Data i only choose id, text, start_date, duration and end_date. For links i choose id, souce, target and type, all types are 0.

I’ve done dragging task together with their dependent task, moving task manualy. Moving Descendants synchronously with the main task( link: https://docs.dhtmlx.com/gantt/desktop__dragging_dependent_tasks.html#movingtasksmanually )

I’ve add to my gantt.aspx this code:

gantt.eachSuccessor = function (callback, root) {
if (!this.isTaskExists(root))
return;

  // remember tasks we've already iterated in order to avoid infinite loops
        var traversedTasks = arguments[2] || {};
        if (traversedTasks[root])
            return;
        traversedTasks[root] = true;

        var rootTask = this.getTask(root);
        var links = rootTask.$source;
        if (links) {
            for (var i = 0; i < links.length; i++) {
                var link = this.getLink(links[i]);
                if (this.isTaskExists(link.target) && !traversedTasks[link.target]) {
                    callback.call(this, this.getTask(link.target));

                    // iterate the whole branch, not only first-level dependencies
                    this.eachSuccessor(callback, link.target, traversedTasks);
                }
            }
        }
    };

    gantt.attachEvent("onTaskDrag", function (id, mode, task, original) {
        var modes = gantt.config.drag_mode;

        if (mode == modes.move) {
            var diff = task.start_date - original.start_date;
            gantt.eachSuccessor(function (child) {
               
                    child.start_date = new Date(+child.start_date + diff);
                    child.end_date = new Date(+child.end_date + diff);
                    gantt.refreshTask(child.id, true);
                }, id);
            }
        return true;
    });
    gantt.attachEvent("onAfterTaskDrag", function (id, mode, e) {
        var modes = gantt.config.drag_mode;
        if (mode == modes.move) {
            gantt.eachSuccessor(function (child) {
                child.start_date = gantt.roundDate(child.start_date);
                child.end_date = gantt.calculateEndDate(child.start_date, child.duration);
                gantt.updateTask(child.id);
            }, id);
        }
    });```


Now i have to add the constrain that a child(target) task can’t move before the end date of father(source). I have to add a Left limit for all tasks, but i have no idea how to do, because i haven’t “parent” on my data details.