Backbone.js collection comparator sort by multiple fields?

Question

  this.col = Backbone.Collection.extend({
    model: M,
    comparator: function(item) {
      return item.get(\"level\");
    }
  });

This above c

Answer 1

String concatenation works fine when sorting multiple fields in ascending order, but it didn't work for me because 1) I had to support asc/desc per field and 2) certain fields were number field (i.e., I want 10 to come after 2 if it is ascending). So, below was a comparator function I used and worked OK for my needs. It assumes the backbone collection has a variable assigned with 'sortConfig', which is an array of JSON objects with field name and sort order direction. For example,

{
    "sort" : [
        {
            "field": "strField",
            "order": "asc"
         },
         {
             "field": "numField",
             "order": "desc"
         },
         ...
     ]
}

With the JSON object above assigned as 'sortConfig' to the collection, the function below will make Backbone sort by strField in ascending order first, then sort by numField in descending order, etc. If no sort order is specified, it sorts ascending by default.

multiFieldComparator: function(one, another) {
    // 'this' here is Backbone Collection
    if (this.sortConfig) {
        for (var i = 0; i < this.sortConfig.length; i++) {
            if (one.get(this.sortConfig[i].field) > another.get(this.sortConfig[i].field)) {
                return ("desc" != this.sortConfig[i].order) ? 1 : -1;
            } else if (one.get(this.sortConfig[i].field) == another.get(this.sortConfig[i].field)) {
                // do nothing but let the loop move further for next layer comparison
            } else {
                return ("desc" != this.sortConfig[i].order) ? -1 : 1;
            }
        }
    }
    // if we exited out of loop without prematurely returning, the 2 items being
    // compared are identical in terms of sortConfig, so return 0
    // Or, if it didn't get into the if block due to no 'sortConfig', return 0
    // and let the original order not change.
    return 0;
}