function ObservableAbstractModel() {
    this._observers = [];
};

ObservableAbstractModel.prototype.setField = function(fieldName, value) {
    this._notifyObservers(fieldName, this.fieldName, value);
    this.fieldName = value;
    return value;
};

ObservableAbstractModel.prototype.getField = function(fieldName) {
    if(this.fieldName) {
        return this.fieldName;
    }
};

ObservableAbstractModel.prototype._notifyObservers = function (changedField, oldValue, newValue) {
    this._observers.forEach(function (observer) {
        observer.update(this, changedField, oldValue, newValue);
    }, this);
};

ObservableAbstractModel.prototype.observe = function (observer) {
    this._observers.push(observer);
};

ObservableAbstractModel.prototype.unobserve = function (observer) {
    var observerIndex = this._observers.lastIndexOf(observer);

    if(observerIndex != -1) {
        this._observers.splice(observerIndex, 1);
        return true;
    }
    return false;
};