How a JMVC Model that uses deferreds could / should look.

Models and deferreds.js

// The GOAL =========================

// 1. define a model 
$.Model("Todo",{
  findOne : function(params, success, error){
     //some deferred gets returned here
  }
},{
  helperMethod : function(){ ... }
})

// 2. Use deferreds and get back model instances.

var todoDeferred = Todo.findOne({}, function(todo){
  todo.helperMethod()
});

todoDeferred.then(function(todo){
  todo.helperMethod()
});


/**
 *  How this looks now, w/o deferreds ===================
 */

findOne : function(params, success, error){
  $.ajax({
    url : "/todo/"+params.id,
    success : this.callback(['wrap',success]) // wrap is inherited from JMVC's model, sudo code for it below
  })
},
wrap : function(data){
  return new this(data);
}

/**
 * How this might work with converter and deferreds
 */

findOne : function(params, success, error){
  $.ajax({
    url : "/todo/"+params.id,
    converter : this.wrap
  }).then(success).error(error)
},

/**
 * How this needs to be done with converters
 */

findOne : function(params, success, error){
  $.ajax({
    url : "/todo/"+params.id,
    converters : {"json model" : this.wrap },
    dataType : "json model"
  }).then(success).error(error)
},


/**
 * consider what if the attributes are in something like {todo : {name: 'title'}}
 */ 

findOne : function(params, success, error){
  $.ajax({
    url : "/todo/"+params.id,
    converters : {"* model" : this.wrap, "* todo" : function(data){  return data.todo }},
    dataType : "json todo model"
  }).then(success).error(error)
},

findOne : "GET /todo/{id} .todo"

I like it. I need to review converters and their syntax, but it's pretty clean.

I think you need a return statement before $.ajax so you can return the promise.