[Rails]form_for select簡易使用

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先創造一個最基本的select：

view.html.erb
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<%= form_for @profile do |f| %>
  <%= f.select(:age, options_for_select(["6+", "12+", "15+", "18+"]), {}, { :class => ’style'}) %>
<% end %>

我們建議把options寫在model：

Profile.rb
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AGE_CLASS = ["6+", "12+", "15+", "18+"].freeze

常數全部大寫是個好習慣
如此簡單的字串array我們也可以改寫為：

Profile.rb
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AGE_CLASS = %w(6+ 12+ 15+ 18+).freeze

把options放到view上：

view.html.erb
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<%= form_for @profile do |f| %>
  <%= f.select(:age, options_for_select(Profile::AGE_CLASS), {}, { :class => ’style'}) %>
<% end %>

如果是想用key, value的話options改為：

Profile.rb
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AGE_CLASS = [["普遍級","6+"], ["保護級","12+"], ["輔導級","15+"], ["限制級","18+"]].freeze

如果想要類似placeholder的空值的話利用include_blank：

view.html.erb
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<%= form_for @profile do |f| %>
  <%= f.select(:age, options_for_select(Profile::AGE_CLASS), {:include_blank => "請選擇"}, { :class => ’style'}) %>
<% end %>

但這樣似乎會讓edit帶入不了表單之前的值，所以我們用預設值selected：

view.html.erb
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<%= form_for @profile do |f| %>
  <%= f.select(:age, options_for_select(Profile::AGE_CLASS, :selected => @profile.age), {:include_blank => "請選擇"}, { :class => ’style'}) %>
<% end %>

這樣如果像是新增或者是先前表單的值並不在options裡面則會跳回include_blank

如果想用html先驗證必填的話加入required：

view.html.erb
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<%= form_for @profile do |f| %>
  <%= f.select(:age, options_for_select(Profile::AGE_CLASS, :selected => @profile.age), {:include_blank => "請選擇"}, { :class => ’style', :required => true}) %>
<% end %>

如果想讓某個options不能選擇的話加入disabled

view.html.erb
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<%= form_for @profile do |f| %>
  <%= f.select(:age, options_for_select(Profile::AGE_CLASS, :selected => @profile.age, :disabled => "18+"), {:include_blank => "請選擇"}, { :class => ’style', :required => true}) %>
<% end %>

甚至可以在裡面寫ruby code，但建議邏輯判斷不要寫在view裡就是了，可以善用helper！