如何在Ruby on Rails中将关系模型序列化为JSON？

# 假设有两个模型：User 和 Post
class User < ApplicationRecord
  has_many :posts
end

class Post < ApplicationRecord
  belongs_to :user
end

# 在控制器中
def index
  users = User.all
  render json: users.to_json(include: :posts)
end

gem 'active_model_serializers', '~> 0.10.0'

# app/serializers/user_serializer.rb
class UserSerializer < ActiveModel::Serializer
  attributes :id, :name, :email
  has_many :posts
end

# app/serializers/post_serializer.rb
class PostSerializer < ActiveModel::Serializer
  attributes :id, :title, :content
  belongs_to :user
end

# app/controllers/users_controller.rb
class UsersController < ApplicationController
  def index
    users = User.all
    render json: users, each_serializer: UserSerializer
  end
end

users = User.includes(:posts).all
render json: users, each_serializer: UserSerializer

class UserSerializer < ActiveModel::Serializer
  attributes :id, :name, :email, :custom_field

  def custom_field
    object.name + " (Custom)"
  end
end