Rails中未持久化的表单对象如何适配User的new与edit操作？

出现该错误的核心原因是：自定义表单对象UserForm没有实现Rails表单辅助方法依赖的persisted?约定，Rails始终将其识别为未持久化的新对象，因此表单永远生成POST请求。而Rails默认的更新路由仅接受PATCH请求，POST请求访问/admin/users/xxx自然会报路由不匹配错误。

步骤1：修改UserForm类适配Rails约定 #

需要补充属性声明、持久化状态代理、编辑场景的原有属性同步逻辑：

class UserForm
  include ActiveModel::Model
  include ActiveModel::Validations::Callbacks

  # 补充缺失的属性声明
  attr_accessor :fname, :lname, :email, :account_id, :existing_user
  # 代理用户对象的id和持久化状态，让表单可以自动识别创建/更新场景
  delegate :id, :persisted?, to: :@user

  def initialize(params = {})
    super(params)
    @account = Account.find(account_id)
    @user = existing_user || User.new
    # 初始化时同步现有用户的属性到表单对象，编辑场景可以自动填充表单
    unless new_record?
      self.fname = @user.fname
      self.lname = @user.lname
      self.email = @user.email
    end
  end

  # 统一提交时的属性赋值逻辑，兼容创建和更新场景
  def save
    @user.assign_attributes(fname: fname, lname: lname, email: email)
    @user.save
    @user
  end

  private
  def new_record?
    !persisted?
  end
end

步骤2：修改表单模板，解耦对@user变量的依赖 #

直接用表单对象自身的persisted?判断路由，不需要额外依赖控制器的@user变量，simple_form会自动根据持久化状态为更新场景生成符合要求的PATCH请求：

<%= simple_form_for @user_form, url: (@user_form.persisted? ? admin_user_path(@user_form) : admin_users_path) do |f| %>
    <%= f.input :fname  %>
    <%= f.input :lname %>
    <%= f.input :email %>
    <%= f.submit %>
<% end %>

步骤3：修改控制器逻辑，统一走表单对象流程 #

你当前的update动作没有走UserForm的逻辑，直接更新@user会导致表单的校验、数据处理逻辑失效，建议和create逻辑统一：

class Admin::UsersController < AdminController
  # 前置查询编辑/更新场景的用户对象
  before_action :find_user, only: [:edit, :update, :show]

  def new
    @user_form = UserForm.new(account_id: current_account.id)
  end

  def create
    @user_form = UserForm.new(user_form_params.merge(account_id: current_account.id))
    if @user = @user_form.save
      flash[:success] = "User created"
      redirect_to admin_user_path(@user)
    else
      render "new"
    end
  end

  def edit
    @user_form = UserForm.new(existing_user: @user, account_id: current_account.id)
  end

  def update
    @user_form = UserForm.new(user_form_params.merge(existing_user: @user, account_id: current_account.id))
    if @user = @user_form.save
      flash[:success] = "User saved"
      redirect_to admin_user_path(@user)
    else
      render "edit"
    end
  end

  private
  def find_user
    @user = User.find(params[:id])
  end

  # 补充参数白名单配置，注意表单对象参数根键为user_form
  def user_form_params
    params.require(:user_form).permit(:fname, :lname, :email)
  end
end

内容的提问来源于stack exchange，提问作者pinkfloyd90