How to pass foreign keys to Rails strong params.

We have a project and a project can have many tasks. Let’s say we have a task form where a user can specify the project the task belongs to. How do you pass the project foreign key through Rails strong params?

# tasks/new.html.haml
= simple_form_for @task do |form|
  = form.input :project_id, collection: Project.all.collect {|c| [c.name, c.id]}
  = form.input :title
  = form.button 'submit', class: 'btn btn-primary'

You want to send :project_id through the Rails form in this case. If you attempt to send :project, you’ll get an error.

Project.all.collect {|c| [c.name, c.id]} maps each project into an array where the first element is the name and the last is the id. Rails form will display name as a dropdown for the user to select but will send the id to the create controller.

# controllers/tasks_controller.rb

def create  
  @task = Task.new(task_params)  
  if @task.save  
    flash[:notice] = 'Task successfully created.'  
    redirect_to tasks_path  
  else  
    render :new  
  end  
end

private

def task_params  
  params.require(:task).permit(:title, :project_id)  
end

That’s it.

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