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Simple Model and Validation Mixins for RubyMotion

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MotionModel: Models, Relations, and Validation for RubyMotion

MotionModel is a DSL for cases where Core Data is too heavy to lift but you are still intending to work with your data, its types, and its relations. It also provides for data validation and actually quite a bit more.


Module Description
ext.rb N/A Core Extensions that provide a few Rails-like niceties. Nothing new here, moving on...
model.rb MotionModel::Model You should read about it in "What Model Can Do". Model is the raison d'etre and the centerpiece of MotionModel.
validatable.rb MotionModel::Validatable Provides a basic validation framework for any arbitrary class. You can also create custom validations to suit your app's unique needs.
input_helpers MotionModel::InputHelpers Helps hook a collection up to a data form, populate the form, and retrieve the data afterwards. Note: MotionModel supports Formotion for input handling as well as these input helpers.
formotion.rb MotionModel::Formotion Provides an interface between MotionModel and Formotion
transaction.rb MotionModel::Model::Transactions Provides transaction support for model modifications

MotionModel is MIT licensed, which means you can pretty much do whatever you like with it. See the LICENSE file in this project.

Bugs, Features, and Issues, Oh My!

The reason this is up front here is that in order to respond to your issues we need you to help us out by reading these guidelines. You can also look at Submissions/Patches near the bottom of this README which restates a bit of this.

That said, all software has bugs, and anyone who thinks otherwise probably is smarter than I am. There are going to be edge cases or cases that our tests don't cover. And that's why open source is great: other people will run into issues we can fix. Other people will have needs we don't have but that are of general utility. And so on.

But… fair is fair. We would make the following requests of you:

  • Debug the code as far as you can. Obviously, there are times when you just won't be able to see what's wrong or where there's some squirrely interaction with RubyMotion.
  • If you are comfortable with the MotionModel code, please try to write a spec that makes it fail and submit a pull request with that failing spec. The isolated test case helps us narrow down what changed and to know when we have the issue fixed. Two things make this even better:
    1. Our specs become more comprehensive; and
    2. If the issue is an interaction between MotionModel and RubyMotion, it's easier to pass along to HipByte and have a spec they can use for a quick hitting test case. Even better, fix the bug and submit that fix and the spec in a pull request.
  • If you are not comfortable with the MotionModel code, then go ahead and describe the issue in as much detail as possible, including backtraces from the debugger, if appropriate.

Now, I've belabored the point about bug reporting enough. The point is, if you possibly can, write a spec.

Issues: Please mark your issues as questions or feature requests, depending on which they are. We'll do all we can to review them and answer questions as quickly as possible. For feature requests, you really can implement the feature in many cases and then submit a pull request. If not, we'll leave it open for consideration in future releases.


Bugs: Please write a failing spec

Issues: Please mark them as question or request

Changes for Existing Users to Be Aware Of

Please see the CHANGELOG for update on changes.

Version 0.4.4 is the first version to be gem-compatible with RubyMotion 2.0

Version 0.3.8 to 0.4.0 is a minor version bump, not a patch version. Upgrading to 0.4.0 will break existing code. To update your code, simply insert the following line:

class ModelWithAdapter
  include MotionModel::Model
  include MotionModel::ArrayModelAdapter # <== Here!

columns :name end

This change lays the foundation for using other persistence adapters. If you don't want to update all your models, install the gem:

$ gem install motion_model -v 0.3.8

or if you are using bundler:

gem motion_model, "0.3.8"

Version 0.3.8 was the last that did not separate the model and persistence concerns.

Getting Going

If you are using Bundler, put this in your Gemfile:

gem 'motion_model'

then do:

bundle install

If you are not using Bundler:

gem install motion_model

then put this in your Rakefile after requiring

require 'motion_model'

If you want to use Bundler from

, put this in your Gemfile:
gem 'motion_model', :git => '[email protected]:sxross/MotionModel.git'

Note that in the above construct, Ruby 1.8.x hash keys are used. That's because Apple's System Ruby is 1.8.7 and won't recognize keen new 1.9.x hash syntax.

What MotionModel Can Do

You can define your models and their schemas in Ruby. For example:

class Task
  include MotionModel::Model
  include MotionModel::ArrayModelAdapter

columns :name => :string, :long_name => :string, :due_date => :date end

class MyCoolController def some_method @task = Task.create :name => 'walk the dog', :long_name => 'get plenty of exercise. pick up the poop', :due_date => '2012-09-15' end end

Side note: The original documentation on this used

for the column that is now
. It turns out Apple reserves
so MotionModel saves you the trouble of finding that particular bug by not allowing you to use it for a column name.

Models support default values, so if you specify your model like this, you get defaults:

class Task
  include MotionModel::Model
  include MotionModel::ArrayModelAdapter

columns :name => :string, :due_date => {:type => :date, :default => '2012-09-15'} end

A note on defaults, you can specify a proc, block or symbol for your default if you want to get fancy. The most obvious use case for this is that Ruby will optimize the assignment of an array so that a default of

always points to the same object. Not exactly what is intended. Wrapping this in a proc causes a new array to be created. Here's an example:
class Foo
  include MotionModel::Model
  include MotionModel::ArrayModelAdapter
  columns  subject: { type: :array, default: ->{ [] } }

This is not constrained to initializing arrays. You can initialize pretty much anything using a proc or block. If you are specifying a block, make sure to use begin/end instead of do/end because it makes Ruby happy.

Here's a different example:

class Timely
  include MotionModel::Model
  include MotionModel::ArrayModelAdapter
  columns  ended_run_at: { type: :time, default: ->{ } }

Note that this uses the "stubby proc" syntax. That is pretty much equivalent to:

columns  ended_run_at: { type: :time, default: lambda { } }

for the previous example.

If you want to use a block, use the begin/end syntax:

columns  ended_run_at: { type: :time, default:

Finally, you can have the default call some class method as follows:

class Timely
  include MotionModel::Model
  include MotionModel::ArrayModelAdapter
  columns  unique_thingie: { type: :integer, default: :randomize }

def self.randomize rand 1_000_000 end end

You can also include the

module to get field validation. For example:
class Task
  include MotionModel::Model
  include MotionModel::ArrayModelAdapter
  include MotionModel::Validatable

columns :name => :string, :long_name => :string, :due_date => :date validates :name, :presence => true end

class MyCoolController def some_method @task = :name => 'walk the dog', :long_name => 'get plenty of exercise. pick up the poop', :due_date => '2012-09-15'

show_scary_warning unless @task.valid?

end end

Important Note: Type casting occurs at initialization and on assignment. That means If you have a field type

, it will be changed from a string to an integer when you initialize the object of your class type or when you assign to the integer field in your class.
a_task = Task.create(:name => 'joe-bob', :due_date => '2012-09-15')     # due_date is cast to NSDate

a_task.due_date = '2012-09-19' # due_date is cast to NSDate

Model Data Types

Currently supported types are:

  • :string
  • :text
  • :boolean
  • :int
  • :float
  • :date
  • :array

You are really not encouraged to stuff big things in your models, which is why a blob type is not implemented. The smaller your data, the less overhead involved in saving/loading.

Special Columns

The two column names,

will be adjusted automatically if they are declared. They need to be of type
. The
column will be set only when the object is created (i.e., on first save). The
column will change every time the object is saved.

Validation Methods

To use validations in your model, declare your model as follows:

class MyValidatableModel
  include MotionModel::Model
  include MotionModel::ArrayModelAdapter
  include MotionModel::Validatable

All other model-y stuff here


Here are some sample validations:

validate :field_name, :presence => true
validate :field_name, :length => 5..8 # specify a range
validate :field_name, :email => true
validate :field_name, :format => /\A\d?\d-\d?\d-\d\d\Z/ # expected string format would be like '12-12-12'

The framework is sufficiently flexible that you can add in custom validators like so:

module MotionModel
  module Validatable
    def validate_foo(field, value, setting)
      # do whatever you need to make sure that the value
      # denoted by *value* for the field corresponds to
      # whatever is passed in setting.

validate :my_field, :foo => 42

In the above example, your new

method will get the arguments pretty much as you expect. The value of the last hash is passed intact via the

You are responsible for adding an error message using:

add_message(field, "incorrect value foo #{the_foo} -- should be something else.")

You must return

from your validator if the value passes validation otherwise

An important note about

once you include
, you have two flavors of save:



|Just saves the data if it is valid (passes validations) or if you have specified
:validate => false
|Saves the data if it is valid, otherwise raises a

Model Instances and Unique IDs

It is assumed that models can be created from an external source (JSON from a Web application or

from the device) or simply be a stand-alone data store. To identify rows properly, the model tracks a special field called
. If it's already present, it's left alone. If it's missing, then it is created for you. Each row id is guaranteed to be unique, so you can use this when communicating with a server or syncing your rowset to a UITableView.

Using MotionModel

  • Your data in a model is accessed in a very ActiveRecord (or Railsey) way. This should make transitioning from Rails or any ORM that follows the ActiveRecord pattern pretty easy. Some of the finder syntactic sugar is similar to that of Sequel or DataMapper.

    • Finders are implemented using chaining. Here is an examples:
    @tasks = Task.where(:assigned_to).eq('bob').and(:location).contains('seattle')
    @tasks.all.each { |task| do_something_with(task) }

    You can use a block with find:

    @tasks = Task.find{|task| =~ /dog/i && task.assigned_to == 'Bob'}

    Note that finders always return a proxy (

    ). You must use
    , or
    to get useful results.
    @tasks = Task.where(:owner).eq('jim')   # => A FinderQuery.
    @tasks.all                              # => An array of matching results.
    @tasks.first                            # => The first result

    You can perform ordering using either a field name or block syntax. Here's an example:

    @tasks = Task.order(:name).all                                  # Get tasks ordered ascending by :name
    @tasks = Task.order{|one, two| two.details <=> one.details}.all # Get tasks ordered descending by :details

    You can implement some aggregate functions using map/reduce:{|task| task.number_of_items}.reduce(:+)                # implements sum{|task| task.number_of_items}.reduce(:+) / @task.count  #implements average
  • Serialization is part of MotionModel. So, in your

    you might do something like this:
      @tasks = Task.deserialize_from_file('tasks.dat')

    and of course on the "save" side:


    After the first serialize or deserialize, your model will remember the file name so you can call these methods without the filename argument.

    Implementation note: that the this serialization of any arbitrarily complex set of relations is automatically handled by

    provided you conform to the coding protocol (which MotionModel does). When you declare your columns,
    understands how to serialize your data so you need take no specific action.

    Persistence will serialize only one model at a time and not your entire data store. This is to allow you to decide what data is serialized when.

    • Relations
    class Task
      include MotionModel::Model
      include MotionModel::ArrayModelAdapter
      columns     :name => :string
      has_many    :assignees

    class Assignee include MotionModel::Model include MotionModel::ArrayModelAdapter columns :assignee_name => :string belongs_to :task end

    Create a task, then create an assignee as a

    related object on that task

    a_task = Task.create(:name => "Walk the Dog") a_task.assignees.create(:assignee_name => "Howard")

    See? It works.

    a_task.assignees.assignee_name # => "Howard" Task.first.assignees.assignee_name # => "Howard"

    Create another assignee but don't save

    Add to assignees collection. Both objects

    are saved.

    another_assignee = => "Douglas") a_task.assignees << another_assignee # adds to relation and saves both objects

    The count of assignees accurately reflects current state

    a_task.assignees.count # => 2

    And backreference access through belongs_to works. # => "Walk the Dog"

There are four ways to delete objects from your data store:

  • object.delete     #
    just deletes the object and ignores all relations
  • object.destroy    #
    deletes the object and honors any cascading declarations
  • Class.delete_all  #
    just deletes all objects of this class and ignores all relations
  • Class.destroy_all #
    deletes all objects of this class and honors any cascading declarations

The key to how the

variants work in how the relation is declared. You can declare:
  class Task
    include MotionModel::Model
    include MotionModel::ArrayModelAdapter
    columns     :name => :string
    has_many    :assignees


will not be considered when deleting
s. However, by modifying the
has_many    :assignees, :dependent => :destroy

When you

an object, all of the objects related to it, and only those related to that object, are also destroyed. So, if you call
and there are 5
related to that task, they will also be destroyed. Any other
are left untouched.

You can also specify:

has_many    :assignees, :dependent => :delete

The difference here is that the cascade stops as the

are deleted so anything related to the assignees remains intact.

Note: This syntax is modeled on the Rails

:dependent => :destroy
options in

Hook Methods

During a save or delete operation, hook methods are called to allow you a chance to modify the object at that point. These hook methods are:


MotionModel makes no distinction between destroy and delete when calling hook methods, as it only calls them when the actual object is deleted. In a destroy operation, during the cascading delete, the delete hooks are called (again) at the point of object deletion.

Note that the method signatures may be different from previous implementations. No longer can you declare a hook method without the


Finally, contrasting hook methods with notifications, the hook methods

are called before the save operation begins and after it completes. However, the notification (covered below) is only issued after the save operation. However... the notification understands whether the operation was a save or update. Rule of thumb: If you want to catch an operation before it begins, use the hook. If you just want to know about it when it happens, use the notification.

The delete hooks happen around the delete operation and, again, allow you the option to mess with the object before you allow the process to go forward (pretty much, the

hook does this).

IMPORTANT: Returning false in a before hook stops the rest of the operation. So, for example, you could prevent the deletion of the last admin by writing something like this:

def before_delete(sender)
  return false if sender.find(:privilege_level).eq('admin').count < 2

Transactions and Undo/Cancel

MotionModel is not ActiveRecord. MotionModel is not a database-backed mapper. The bottom line is that when you change a field in a model, even if you don't save it, you are partying on the central object store. In part, this is because Ruby copies objects by reference, so when you do a find, you get a reference to the object in the central object store.

The upshot of this is that MotionModel can be wicked fast because it isn't moving much more than pointers around in memory when you do assignments. However, it can be surprising if you are used to a database-backed mapper.

You could easily build an app and never run across a problem with this, but in the case where you present a dialog with a cancel button, you will need a way to back out. Here's how:

# in your form presentation view...
include MotionModel::Model::Transactions

person.transaction do result = do_something_that_changes_person person.rollback unless result end

def do_something_that_changes_person


return it_worked end

You can have nested transactions and each has its own context so you don't wind up rolling back to the wrong state. However, everything that you wrap in a transaction must be wrapped in the

block. That means you need to have some outer calling method that can wrap a series of delegated changes. Explained differently, you can't start a transaction, have a delegate method handle a cancel button click and roll back the transaction from inside the delegate method. When the block is exited, the transaction context is removed.


Notifications are issued on object save, update, and delete. They work like this:

def viewDidAppear(animated)
  # other stuff here to set up your view

NSNotificationCenter.defaultCenter.addObserver(self, selector:'dataDidChange:', name:'MotionModelDataDidChangeNotification', object:nil) end

def viewWillDisappear(animated) super NSNotificationCenter.defaultCenter.removeObserver self end

... more stuff ...

def dataDidChange(notification)

code to update or refresh your view based on the object passed back

and the userInfo. userInfo keys are:






In your

notification handler, you can respond to the
notification any way you like, but in the instance of a tableView, you might want to use the id of the object passed back to locate the correct row in the table and act upon it instead of doing a wholesale

Note that if you do a delete_all, no notifications are issued because there is no single object on which to report. You pretty much know what you need to do: Refresh your view.

This is implemented as a notification and not a delegate so you can dispatch something like a remote synch operation but still be confident you will be updating the UI only on the main thread. MotionModel does not currently send notification messages that differentiate by class, so if your UI presents

s and you get a notification that an
has changed:
class Task
  include MotionModel::Model
  include MotionModel::ArrayModelAdapter
  has_many :assignees
  # etc

class Assignee include MotionModel::Model include MotionModel::ArrayModelAdapter belongs_to :task




task = Task.create :name => 'Walk the dog' # Triggers notification with a task object task.assignees.create :name => 'Adam' # Triggers notification with an assignee object


We set up observers for MotionModelDataDidChangeNotification someplace and:

def dataDidChange(notification) if notification.object is_a?(Task)

Update our UI


This notification is not for us because

We don't display anything other than tasks


The above example implies you are only presenting, say, a list of tasks in the current view. If, however, you are presenting a list of tasks along with their assignees and the assignees could change as a result of a background sync, then your code could and should recognize the change to assignee objects.

Core Extensions

  • String#humanize
  • String#titleize
  • String#empty?
  • String#singularize
  • String#pluralize
  • NilClass#empty?
  • Array#empty?
  • Hash#empty?
  • Symbol#titleize

Also in the extensions is a

class to log stuff to the console. It uses NSLog so you will have a separate copy in your application log. This may be preferable to
just because it's easier to spot in your code and it gives you the exact level and file/line number of the info/warning/error in your console output:
  • Debug.warning(message)
  • Debug.error(message)
  • Debug.silence / Debug.resume to turn on and off logging
  • Debug.colorize (true/false) for pretty console display

Finally, there is an inflector singleton class based around the one Rails has implemented. You don't need to dig around in this class too much, as its core functionality is exposed through two methods:

String#singularize String#pluralize

These work, with the caveats that 1) The inflector is English-language based; 2) Irregular nouns are not handled; 3) Singularizing a singular or pluralizing a plural makes for good cocktail-party stuff, but in code, it mangles things pretty badly.

You may want to get into customizing your inflections using:

  • Inflector.inflections.singular(rule, replacement)
  • Inflector.inflections.plural(rule, replacement)
  • Inflector.inflections.irregular(rule, replacement)

These allow you to add to the list of rules the inflector uses when processing singularize and pluralize. For each singular rule, you will probably want to add a plural one. Note that order matters for rules, so if your inflection is getting chewed up in one of the baked-in inflections, you may have to use Inflector.inflections.reset to empty them all out and build your own.

Of particular note is Inflector.inflections.irregular. This is for words that defy regular rules such as 'man' => 'men' or 'person' => 'people'. Again, a reversing rule is required for both singularize and pluralize to work properly.



does not, by default perform any serialization. That's because how often which parts of your object graph are serialized can affect application performance. However, you will want to use the serialization features. Here they are:
YourModel.deserialize_from_file(file_name = nil)

YourModel.serialize_to_file(file_name = nil)

What happens here? When you want to save a model, you call

. Each model's data must be saved to a different file so name them accordingly. If you have a model that contains related model objects, you may want to save both models. But you have complete say over that and the responsibility to handle it.

When you call

, your model is populated from the file previously serialized.

Formotion Support


MotionModel has support for the cool Formotion gem. Note that the Formotion project on GitHub appears to be way ahead of the gem on Rubygems, so you might want to build it yourself if you want the latest gee-whiz features (like

, as I've shown in the first example).

High-Level View

class Event
  include MotionModel::Model
  include MotionModel::Formotion  # <== Formotion support

columns :name => :string, :date => {:type => :date, :formotion => {:picker_type => :date_time}}, :location => :string end

This declares the class. The only difference is that you include

. If you want to pass additional information on to Formotion, simply include it in the
hash as shown above.

Note: the

stuff in the
specification is something I'm still thinking about. Read on to find out about the two alternate syntaxes for

Details About

There are two alternate syntaxes for calling this. The initial, or "legacy" syntax is as follows:

to_formotion(form_title, expose_auto_date_fields, first_section_title)

In the legacy syntax, all arguments are optional and sensible defaults are chosen. However, when you want to tune how your form is presented, the syntax gets a bit burdensome. The alternate syntax is:


The options hash looks a lot like a Formotion hash might, except without the data. Here is an example:

{title: 'A very fine form',
 sections: [
  {title:  'First Section',
   fields: [:name, :gender]
  {title:  'Second Section',
   fields: [:address, :city, :state]

Note that in this syntax, you can specify a button in the fields array:

{title: 'A very fine form',
 sections: [
  {title:  'First Section',
   fields: [:name, :gender]
  {title:  'Second Section',
   fields: [:address, :city, :state, {type: :submit, title: 'Ok'}]

This specifies exactly what titles and fields appear where and in what order.

Finally, you can specify a button:

{title: 'A very fine form',
 sections: [
  {title:  'First Section',
   fields: [:name, :gender]
  {title:  'Second Section',
   fields: [:address, :city, :state, {type: :submit, title: 'Ok'}],
   {type: :button, title: 'add now!!!'}

How Values Are Produced for Formotion

MotionModel has sensible defaults for each type supported, so any field of

type will default to a date picker in the Formotion form. However, if you want it to be a string for some reason, just specify this in
:date => {:type => :date, :formotion => {:type => :string}}

To initialize a form from a model in your controller:

@form ='event details')) # Legacy syntax
@form_controller = MyFormController.alloc.initWithForm(@form)

The magic is in:


The autodate fields `createdat

updated_at` are not sent to Formotion by default. If you want them sent to Formotion, set the second argument to true. E.g.,
@form ='event details', true))

On the flip side you do something like this in your Formotion submit handler:


This performs sets on each field. You'll, of course, want to check your validations before dismissing the form.

Moreover, Formotion support allows you to split one model fields in sections. By default all fields are put in a single untitled section. Here is a complete example:

class Event
  include MotionModel::Model
  include MotionModel::Formotion  # <== Formotion support

columns :name => :string, :date => {:type => :date, :formotion => {:picker_type => :date_time}}, :location => {:type => :string, :formotion => {:section => :address}}

has_formotion_sections :address => {:title => "Address"} end

This will create a form with the

fields presented first, then a section titled 'Address' will contain the

If you want to add a title to the first section, provide a :firstsectiontitle argument to

@form ='event details', true, 'First Section Title'))


Please raise an issue on GitHub if you find something that doesn't work, some syntax that smells, etc.

If you want to stay on the bleeding edge, clone yourself a copy (or better yet, fork one).

Then be sure references to motion_model are commented out or removed from your Gemfile and/or Rakefile and put this in your Rakefile:

require "~/github/local/MotionModel/lib/motion_model.rb"


is where I cloned it, but you can put it anyplace. Next, make sure you are following the project on GitHub so you know when there are changes.

Submissions/Patches/Bug Reports

For a submission, do this:

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request

For a bug report, the best bet is follow the above steps, but for #2 and 4, use the issue number in the branch. Once you have created the pull request, reference it in the issue.

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