If parent start date is null, it takes its child start date. how to avoid that?

In my case i have some task which have start_date as null but it takes it’s child or parent start date. how to restrict that and show those task with null start date?

Projects ignore start and end dates, you can use auto_types config and projects without subtasks will be converted into tasks. And as soon as you add a subtask to any task, it becomes a project:
Here is a sample:

but in that case it don’t allow me to change start or end date of parent task. i want to change that by drag and drop.

@mukesh1390, you can use drag_project option:
Here is the sample where you can drag projects: