How do I set a default text input size for string fields in Simple Form using an initializer?

Below is one approach to make Simple Form treat all text-like (i.e. string) attributes without applying a default “size” option, reserving a larger textarea only when you explicitly request it with as: :text.

In your config/initializers/simple_form.rb you can tweak two things:

1. Tell Simple Form to map database columns of type text to the :string input (this lets you override the default that might choose a textarea for text columns):

RUBYCopied
SimpleForm.setup do |config|
  # If your DB has text columns but you want them rendered using a text_field,
  # map them to :string.
  config.input_mappings = { /text/ => :string }
  
  # rest of your configuration…
end

2. Remove any default :size HTML attribute from string inputs by modifying your default wrapper. For example, if your default wrapper adds size automatically you can override it:

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SimpleForm.setup do |config|
  config.wrappers :default, tag: "div", class: "input", error_class: "error" do |b|
    b.use :label
    # Remove the size attribute by setting input_html option explicitly.
    b.use :input, input_html: { size: nil }
    b.use :error, wrap_with: { tag: "span", class: "error_message" }
    b.use :hint,  wrap_with: { tag: "p", class: "hint" }
  end
end

With these adjustments, if you do a simple form input normally (which by default is rendered as a text_field for strings), it won’t include an unwanted size attribute. And if you want a larger text area for multiline input you can still force it using:

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<%= f.input :description, as: :text %>

Keep in mind that changing input_mappings may affect how all text columns are rendered in your application so be sure this change suits your overall needs.

This solution shows it is indeed possible to adjust default input options in Simple Form via the initializer.