新建电影的时候，走的这段代码并没有_id，插入的是空

app.get('/admin/movie',function(req,res){
	res.render('admin',{
		title:'后台录入页',
		movie:{
			title:'',
			doctor:'',
			country:'',
			year:'',
			poster:'',
			summary:'',
			language:'',
		}
	})
});

input(type='hidden',name='movie[_id]',value='#{movie._id}')

movie._id这个是怎么找到的