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<!DOCTYPE html>
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<title>Slides for
Ruby Object Orientation — Ruby on Rails Guides
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<section>
<h1>Ruby Object Orientation</h1><p>This guide will take a closer look at objects, classes and modules in Ruby.</p><p>After finishing this guide you will</p>
<ul>
<li>know how to write object methods and use object variables (properties)</li>
<li>know how to write class methods and use class variables (properties)</li>
</ul>
<p><small>Slides - use arrow keys to navigate, esc to return to page view, f for fullscreen</small></p>
</section>
<section><a class='slide_break' href='ruby_oo.html#slide-0'>▻</a>
<h2 id="to-be-written"><a class="anchorlink" href="#to-be-written"><span>1</span> To Be Written</a></h2></section>
<section><a class='slide_break' href='ruby_oo.html#slide-1'>▻</a>
<h2 id="an-investigation-into-declarations"><a class="anchorlink" href="#an-investigation-into-declarations"><span>2</span> An investigation into Declarations:</a></h2><p>In <a href="rails_associations_and_validations.html">Rails: Associations and Validations</a> we learned that Validation are declared in the model:</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="k">class</span> <span class="nc">Tweet</span> <span class="o"><</span> <span class="no">ApplicationRecord</span>
<span class="n">validates_presence_of</span> <span class="ss">:status</span>
<span class="k">end</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="class Tweet < ApplicationRecord
validates_presence_of :status
end
">Copy</button>
</div>
<p>But what is really happening here?</p><p><code>validates_presence_of</code> is called when the class is defined. it is called only once.</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="k">class</span> <span class="nc">Ruby</span>
<span class="k">def</span> <span class="nf">validates_presence_of</span> <span class="n">x</span>
<span class="nb">puts</span> <span class="s2">"I should really check for property </span><span class="si">#{</span><span class="n">x</span><span class="si">}</span><span class="s2">"</span>
<span class="k">end</span>
<span class="n">validates_presence_of</span> <span class="ss">:color</span>
<span class="k">end</span>
<span class="c1"># in `<class:Ruby>': undefined method `validates_presence_of' for Ruby:Class (NoMethodError)</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="class Ruby
def validates_presence_of x
puts "I should really check for property #{x}"
end
validates_presence_of :color
end
# in `<class:Ruby>': undefined method `validates_presence_of' for Ruby:Class (NoMethodError)
">Copy</button>
</div>
<p><code>validates_presence_of</code> cannot be a normal method, because such a method is not defined yet
when the class is defined. so it needs to be a class method.</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="k">class</span> <span class="nc">Ruby</span>
<span class="k">def</span> <span class="nc">self</span><span class="o">.</span><span class="nf">validates_presence_of</span> <span class="n">x</span>
<span class="nb">puts</span> <span class="s2">"I should really check for property </span><span class="si">#{</span><span class="n">x</span><span class="si">}</span><span class="s2">"</span>
<span class="k">end</span>
<span class="n">validates_presence_of</span> <span class="ss">:color</span>
<span class="k">end</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="class Ruby
def self.validates_presence_of x
puts "I should really check for property #{x}"
end
validates_presence_of :color
end
">Copy</button>
</div>
<p>....</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="k">class</span> <span class="nc">ValidatableStuff</span>
<span class="nb">attr_accessor</span> <span class="ss">:data</span>
<span class="nb">attr_accessor</span> <span class="ss">:errors</span>
<span class="k">def</span> <span class="nc">self</span><span class="o">.</span><span class="nf">validates_presence_of</span> <span class="n">x</span>
<span class="nb">puts</span> <span class="s2">"the class </span><span class="si">#{</span><span class="nb">self</span><span class="si">}</span><span class="s2"> should really check for </span><span class="si">#{</span><span class="n">x</span><span class="si">}</span><span class="s2"> - but how?"</span>
<span class="vc">@@validator_for</span> <span class="o">=</span> <span class="n">x</span>
<span class="k">end</span>
<span class="k">def</span> <span class="nf">initialize</span><span class="p">(</span><span class="o">**</span><span class="n">data</span><span class="p">)</span>
<span class="vi">@data</span> <span class="o">=</span> <span class="n">data</span>
<span class="k">end</span>
<span class="k">def</span> <span class="nf">save</span>
<span class="nb">puts</span> <span class="s2">"I am trying to save the data of a </span><span class="si">#{</span><span class="nb">self</span><span class="p">.</span><span class="nf">class</span><span class="si">}</span><span class="s2"> Object. the data is </span><span class="si">#{</span><span class="nb">self</span><span class="p">.</span><span class="nf">data</span><span class="si">}</span><span class="s2">"</span>
<span class="k">if</span> <span class="nb">self</span><span class="p">.</span><span class="nf">data</span><span class="p">.</span><span class="nf">keys</span><span class="p">.</span><span class="nf">include?</span><span class="p">(</span> <span class="vc">@@validator_for</span> <span class="p">)</span>
<span class="nb">puts</span> <span class="s2">"this is ok, </span><span class="si">#{</span><span class="vc">@@validator_for</span><span class="si">}</span><span class="s2"> is set"</span>
<span class="k">return</span> <span class="kp">true</span>
<span class="k">else</span>
<span class="nb">puts</span> <span class="s2">"this is not ok, </span><span class="si">#{</span><span class="vc">@@validator_for</span><span class="si">}</span><span class="s2"> needs to be set"</span>
<span class="nb">self</span><span class="p">.</span><span class="nf">errors</span> <span class="o">=</span> <span class="s2">"</span><span class="si">#{</span><span class="vc">@@validator_for</span><span class="si">}</span><span class="s2"> needs to be set"</span>
<span class="k">return</span> <span class="kp">false</span>
<span class="k">end</span>
<span class="k">end</span>
<span class="k">end</span>
<span class="k">class</span> <span class="nc">Ruby</span> <span class="o"><</span> <span class="no">ValidatableStuff</span>
<span class="k">def</span> <span class="nf">x</span>
<span class="k">end</span>
<span class="n">x</span>
<span class="n">validates_presence_of</span> <span class="ss">:color</span>
<span class="k">end</span>
<span class="k">class</span> <span class="nc">Diamond</span> <span class="o"><</span> <span class="no">ValidatableStuff</span>
<span class="n">validates_presence_of</span> <span class="ss">:carat</span>
<span class="k">end</span>
<span class="n">r1</span> <span class="o">=</span> <span class="no">Ruby</span><span class="p">.</span><span class="nf">new</span>
<span class="k">if</span> <span class="n">r1</span><span class="p">.</span><span class="nf">save</span>
<span class="nb">puts</span> <span class="s2">"saved"</span>
<span class="k">else</span>
<span class="nb">puts</span> <span class="s2">"errors: </span><span class="si">#{</span><span class="n">r1</span><span class="p">.</span><span class="nf">errors</span><span class="si">}</span><span class="s2">"</span>
<span class="k">end</span>
<span class="n">r2</span> <span class="o">=</span> <span class="no">Ruby</span><span class="p">.</span><span class="nf">new</span><span class="p">(</span><span class="ss">color: </span><span class="s1">'yellow'</span><span class="p">)</span>
<span class="n">r2</span><span class="p">.</span><span class="nf">save</span>
<span class="n">d1</span> <span class="o">=</span> <span class="no">Diamond</span><span class="p">.</span><span class="nf">new</span>
<span class="n">d1</span><span class="p">.</span><span class="nf">save</span>
<span class="n">d2</span> <span class="o">=</span> <span class="no">Diamond</span><span class="p">.</span><span class="nf">new</span><span class="p">(</span><span class="ss">carat: </span><span class="mi">10</span><span class="p">)</span>
<span class="n">d2</span><span class="p">.</span><span class="nf">save</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="class ValidatableStuff
attr_accessor :data
attr_accessor :errors
def self.validates_presence_of x
puts "the class #{self} should really check for #{x} - but how?"
@@validator_for = x
end
def initialize(**data)
@data = data
end
def save
puts "I am trying to save the data of a #{self.class} Object. the data is #{self.data}"
if self.data.keys.include?( @@validator_for )
puts "this is ok, #{@@validator_for} is set"
return true
else
puts "this is not ok, #{@@validator_for} needs to be set"
self.errors = "#{@@validator_for} needs to be set"
return false
end
end
end
class Ruby < ValidatableStuff
def x
end
x
validates_presence_of :color
end
class Diamond < ValidatableStuff
validates_presence_of :carat
end
r1 = Ruby.new
if r1.save
puts "saved"
else
puts "errors: #{r1.errors}"
end
r2 = Ruby.new(color: 'yellow')
r2.save
d1 = Diamond.new
d1.save
d2 = Diamond.new(carat: 10)
d2.save
">Copy</button>
</div>
</section>
<section><a class='slide_break' href='ruby_oo.html#slide-2'>▻</a>
<h3 id="online-resources"><a class="anchorlink" href="#online-resources"><span>2.1</span> Online Resources</a></h3>
<ul>
<li><a href="http://rubylearning.com/satishtalim/tutorial.html">learningruby.com tutorial</a></li>
</ul>
</section>
<section><a class='slide_break' href='ruby_oo.html#slide-3'>▻</a>
<h3 id="books"><a class="anchorlink" href="#books"><span>2.2</span> Books</a></h3>
<ul>
<li><a href="https://www.poodr.com/">Metz, Sandy(2017): Practical Object-Oriented Design in Ruby</a></li>
</ul>
</div></section>
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