Rails 4 ActiveRecord，如果记录存在，请使用id，否则创建一个新记录

创建员工后，将为其授予标题。如果标题是唯一的，则记录将正常保存。如果标题不是唯一的，我想找到现有的标题，并改用它。我不知道如何在create动作中做到这一点。

雇主

class Employee < ActiveRecord::Base
  belongs_to :title, :class_name => :EmployeeTitle, :foreign_key => "employee_title_id"
  accepts_nested_attributes_for :title
end

loyal_title.rb

class EmployerTitle < ActiveRecord::Base
  has_many :employees
  validates :name, presence: true, length: { maximum: 50 },
            uniqueness: { case_sensitive: true }
end

new.html.erb

<%= f.simple_fields_for :title do |title| %>
    <%= title.input :name, label: "Title" %>
<% end %>

employee_controller.rb

def create
  if EmployeeTitle.exists?(name: employee_params[:title_attributes][:name])
    # find title and use it?
  else
    @employee = current_user.employee.build(employee_params)
  end
  if @employee.save
    flash[:success] = "Employee #{@employee.title.name} created."
    redirect_to @employee
  else
    render 'new'
  end
end

编辑：使用first_or_create

def create
  EmployeeTitle.where(name: employee_params[:title_attributes][:name]).first_or_create do |title|
    @employee = current_user.employees.build(employee_params, :title => title)
  end
  if @employee.save
    flash[:success] = "Employee #{@employee.title.name} created."
    redirect_to @employee
  else
    render 'new'
  end
end

这使@employee超出范围。错误：nil：NilClass的未定义方法“保存”。

此外，如果我这样做，则无论其余员工数据是否有效，都不会创建标题吗？

使用私有方法

employee.rb

  private
    def title_attributes=(attributes)
      self.title = EmployeeTitle.find_or_create_by_name(name: attributes[:name])
    end

尚未设置该值。我收到“不能为空”的验证错误。参数包括

employee: !ruby/hash:ActionController::Parameters
  title: !ruby/hash:ActiveSupport::HashWithIndifferentAccess
    name: Consultant

！ruby / hash：ActiveSupport :: HashWithIndifferentAccess以前不存在。

employee_params

  private
    def employee_params
      params.require(:employee).permit(
          title_attributes: [:id, :name],
      )
    end