Question

This is a follow up to a question: KnockoutJS Sortable group observableArray by field and conditionally sort

There are two further things I am battling to achieve. First when a nested list item is dragged to another list leaving the parent empty I would like to remove the parent. I have done this by creating an afterMove function and checking if the sourceParent length is 0. Then I look through the routes to see if any have an empty tasks array and remove accordingly. I would like to know if this is an efficient solution. I also have to remove the tasks otherwise the tasks subscription adds duplicates when removing scheduled tasks.

Second and most importantly the base object (Task) has an order property. I would like to bind this to the sortable order so that when the tasks are dragged around the Scheduled list the order property is updated. How do I access the order of other list items from the sortable callback?

Please see the following this Fiddle.

Any assistance would be greatly appreciated.

Answer 1

For the first issue, there is a slightly optimized way that you could do it. arg.sourceParent is contained in the tasksByRoute item that you want to remove. The remove function can take a function to run against the items. So, you could write it like:

self.afterMoveCallback = function(arg) {
    if (arg.sourceParent().length === 0) {
        self.tasksByRoute.remove(function(route) {
           return route.tasks === arg.sourceParent; 
        });
    }
};

For the second issue, I really like to use an extension that will automatically track the order in an observableArray. It would look something like:

//track an index on items in an observableArray
ko.observableArray.fn.indexed = function(prop) {
    prop = prop || 'index';
   //whenever the array changes, make one loop to update the index on each
   this.subscribe(function(newValue) {
       if (newValue) {
           var item;
           for (var i = 0, j = newValue.length; i < j; i++) {
               item = newValue[i];
               if (!ko.isObservable(item[prop])) {
                  item[prop] = ko.observable();
               }
               item[prop](i);  //add 1 here if you don't want it to be zero based
           }
       }   
   }); 

   //initialize the index
   this.valueHasMutated(); 
   return this;
};

in your case, you would use it like:

self.scheduledTasks = ko.observableArray([
    new Task(8, 4, "Route 4", "Cust 8", 1),
    new Task(9, 4, "Route 4", "Cust 9", 2),
    new Task(10, 5, "Route 5", "Cust 10")
    ]).indexed("order");

Here is a sample updated with both of these changes: http://jsfiddle.net/rniemeyer/usVKQ/