A example of sinatra with mongodb

app.rb

require 'mongoid'
require 'sinatra'
require 'json'
#加上:development避免mongoid找不到环境而报错
#预先在"config/mongoid.yml"创建了, 详情见以上链接. 
Mongoid.load!(File.join(File.dirname(__FILE__), 'config', 'mongoid.yml'), :development) 
#无需声明id字段, mongoid会自动加上
class Post
  include Mongoid::Document

  field :title, type: String
  field :body, type: String


  has_many :comments
end

class Comment
  include Mongoid::Document

  field :name, type: String
  field :message, type: String

  belongs_to :post
end

def send_err(code,msg) #定义报错函数
  halt code, {'code': code ,'message': msg}.to_json
end

before do
  content_type :json #设定每一个路由的content_type
end

get '/' do
  '{"text":"Hello World"}'
end

get '/posts' do
  Post.all.to_json
end

post '/posts' do
  send_err 415,"type error"  unless request.env['CONTENT_TYPE'] == 'application/json' #halt 即HTTP状态码
  payload= JSON.parse(request.body.read) #如果是JSON的话payload这个变量就装着一个hash, 如果不是JSON就是一个string
  if payload.is_a?(Hash) #是hash才接着走
    if payload.key?("body") and payload.key?("title") #是否存在这两个字段? 
      post = Post.create!(body: payload['body'], title: payload['title'])
      post.to_json #to_json 会将这个Object转换成JSON(如果可以的话, 不行就变成String)发回去
    else
      halt 400, payload.to_json
    end
    else #返回400, 请求数据原封不动丢回去
      halt 400, payload.to_json
  end
end

get '/posts/:post_id' do |post_id|
  begin
    post = Post.find(post_id)
  rescue => err #返回报错信息
    send_err(404,err.to_s)
  end
  post.attributes.merge(
  comments: post.comments,
  ).to_json
end

post '/posts/:post_id/comments' do |post_id|
  send_err(415,"type error") unless request.env['CONTENT_TYPE'] == 'application/json'
  payload= JSON.parse(request.body.read)
  begin
    post = Post.find(post_id)
  rescue => err
    send_err(404,err.to_s)
  end
  if payload.is_a?(Hash)
    if (['name','message']-payload.keys).empty?
      comment = post.comments.create!(name:payload['name'],message:payload['message'])
      comment.to_json
    else
      halt 400, payload.to_json
    end
  else
    halt 400, payload.to_json
  end
end