I'm trying to create a todo app using node.js, mongoose and backbone for learning purposes.
Up till now I defined these models: 

```
var TaskSchema = new mongoose.Schema({
    title: { type:String },
    content: { type:String } ,
    created: {type:Date, 'default':Date.now},
    due: {type:Date},
    accountId: {type:mongoose.Schema.ObjectId}
});

var Task = mongoose.model('Task',TaskSchema);

var AccountSchema = new mongoose.Schema({
    email: { type:String, unique: true},
    password: { type:String } ,
    name: { first: {type:String}, 
        last: { type:String } },
    birthday: {
        day: {type:Number, min:1, max:31, required:false},
        month: {type:Number, min:1, max:12, required:false},
        year: {type:Number}

    },
    photoUrl: {type:String},
    biography:{type:String},
    tasks:[Task]
});

var Account = mongoose.model('Account',AccountSchema);

```

In addition, I also have the following method for **adding a task**:

```
var enter_new_task = function(options,callback){
    var title = options.title;
    var content = options.content;
    var due = options.due;
    var account = options.account;
    var task = new Task({
        title: title,
        content: content,
        due: due,
        accountId: account._id
    });
    account.tasks.push(task);
    account.save(function(err) {
        if ( err ) {
            console.log("Error while saving task: " + err);
        }else{
            callback();
        }
    })
}

```

But when I indeed add a task, I get an error that says: 

> 
> "Object {} has no method 'cast'"
> 
> 
> 

With the following stack trace:

```
   at Array.MongooseArray._cast (/home/lior/workspace/todo_express/node_modules/mongoose/lib/types/array.js:107:30)
    at Object.map (native)
    at Array.MongooseArray.push (/home/lior/workspace/todo_express/node_modules/mongoose/lib/types/array.js:261:23)
    at Object.enter_new_task (/home/lior/workspace/todo_express/models/Account.js:107:17)
    at /home/lior/workspace/todo_express/app.js:104:18
    at Promise.<anonymous> (/home/lior/workspace/todo_express/models/Account.js:41:4)
    at Promise.<anonymous> (/home/lior/workspace/todo_express/node_modules/mongoose/node_modules/mpromise/lib/promise.js:162:8)
    at Promise.EventEmitter.emit (events.js:95:17)
    at Promise.emit (/home/lior/workspace/todo_express/node_modules/mongoose/node_modules/mpromise/lib/promise.js:79:38)
    at Promise.fulfill (/home/lior/workspace/todo_express/node_modules/mongoose/node_modules/mpromise/lib/promise.js:92:20)
9

```

It seems that the problem is with the line that the new task to the tasks array.

Couldn't find anything on google or stack so I wonder, does anyone have an idea about what went wrong?

Thanks!