Usage - Callbacks
You may optionally specify a callback to be executed on model creation/instantiation as a third parameter when defining a definition. We will pass your model instance as the first parameter to the closure if you specify one. We additionally pass a boolean as the second parameter that will be true if the model is being persisted to the database (the create function was used), and false if it's not being persisted (the instance function was used). We're using the isPendingOrSaved function under the hood here. Note that if you specify a callback and use the create function, we will try to save your model to the database both before and after we execute the callback.