为什么我收到 null
而不是 真/假对于 is_read 从 API 调用资源时?
问题:可能与render json:
有关内部?
这是我第一次看到这个巫术,所以请多多包涵。寻找好的答案:)
$ curl -X GET -H localhost:3000/api/v1/alerts/1/show | python -m json.tool
{
"body": "Deserunt laboriosam quod consequuntur est dolor cum molestias.",
"created_at": "2015-03-22T15:02:01.927Z",
"id": 1,
"is_read": null,
"subtitle": "Aspernatur non voluptatem minus qui laudantium molestiae.",
"title": "Et nemo magni autem similique consequuntur.",
"updated_at": "2015-03-22T15:02:01.927Z"
}
-i
HTTP/1.1 200 OK
X-Frame-Options: SAMEORIGIN
X-Xss-Protection: 1; mode=block
X-Content-Type-Options: nosniff
Content-Type: application/json; charset=utf-8
Etag: "3232ec2058ffb13db1f9244366fe2ea8"
Cache-Control: max-age=0, private, must-revalidate
X-Request-Id: c520cabe-6334-4997-956b-d1f21724b80c
X-Runtime: 0.016337
Server: WEBrick/1.3.1 (Ruby/2.1.2/2014-05-08)
Date: Sun, 22 Mar 2015 15:28:21 GMT
Content-Length: 300
Connection: Keep-Alive
Rails 控制台:Alert.find(1)
Alert Load (1.1ms) SELECT "alerts".* FROM "alerts" WHERE "alerts"."id" = $1 LIMIT 1 [["id", 1]]
=> #<Alert id: 1, title: "Et nemo magni autem similique consequuntur.", subtitle: "Aspernatur non voluptatem minus qui laudantium mol...", body: "Deserunt laboriosam quod consequuntur est dolor cu...", is_read: false, created_at: "2015-03-22 15:02:01", updated_at: "2015-03-22 15:02:01">
当我调用 #to_json
时会发生奇怪的事情Alert.find(1).to_json
Alert Load (4.1ms) SELECT "alerts".* FROM "alerts" WHERE "alerts"."id" = $1 LIMIT 1 [["id", 1]]
=> "{\"id\":1,\"title\":\"Et nemo magni autem similique consequuntur.\",\"subtitle\":\"Aspernatur non voluptatem minus qui laudantium molestiae.\",\"body\":\"Deserunt laboriosam quod consequuntur est dolor cum molestias.\",\"is_read\":null,\"created_at\":\"2015-03-22T15:02:01.927Z\",\"updated_at\":\"2015-03-22T15:02:01.927Z\"}"
当 is_read 为真时也会发生这种情况。更多信息:
Rails 4.1.7、Ruby 2.1.2、Postgresql
警报
create_table "alerts", force: true do |t|
t.string "title"
t.string "subtitle"
t.text "body"
t.boolean "is_read", default: false, null: false
t.datetime "created_at"
t.datetime "updated_at"
end
用于填充数据库的脚本:Alert.populate 100 do |alert|
alert.title = Faker::Lorem.sentence(3)
alert.subtitle = Faker::Lorem.sentence(3)
alert.body = Faker::Lorem.sentence(3)
alert.is_read = false
end
Controller :def show
alert = Alert.find(params[:id])
render json: alert
end
编辑 2015 年 3 月 26 日
irb(main):013:0> Alert.find(1)
Alert Load (0.6ms) SELECT "alerts".* FROM "alerts" WHERE "alerts"."id" = $1 LIMIT 1 [["id", 1]]
=> #<Alert id: 1, title: "Test", subtitle: "waaat?", body: "heeeelp", is_read: false, created_at: "2015-03-26 15:49:32", updated_at: "2015-03-26 15:56:51">
irb(main):014:0> a.body
=> "heeeelp"
irb(main):015:0> a.title
=> "Test"
irb(main):016:0> a.is_read
=> nil
irb(main):017:0> a["is_read"]
=> false
irb(main):018:0> a.update_attributes(is_read: true)
(0.4ms) BEGIN
SQL (0.5ms) UPDATE "alerts" SET "is_read" = $1, "updated_at" = $2 WHERE "alerts"."id" = 1 [["is_read", "t"], ["updated_at", "2015-03-26 15:57:26.645210"]]
(2.1ms) COMMIT
=> true
irb(main):019:0> a["is_read"]
=> true
最终:这是因为模型中有 attr_reader :is_read 。删除它将导致正确的序列化。有人可以解释一下吗?
最佳答案
Final: it was because there was attr_reader :is_read in the model. Removing that it will result in a correct serialization. Can someone explain this?
ActiveRecord 通过为每个属性创建一个 getter 方法来帮助将数据库字段映射到 Ruby 类上的方法,该方法从内部属性存储(变量)中提取值。
当您定义
attr_reader :is_read
,这实际上是以下的简写:# app/mode/alert.rb
def is_read
@is_read
end
ActiveRecord::Base
提供的你的 getter 方法将被这个新定义的方法掩盖。这可能是出乎意料的,而且乍一看绝对像是巫术。:attr_reader
的行为是(有点稀疏)记录在这里:Creates instance variables and corresponding methods that return the value of each instance variable.
http://ruby-doc.org/core-1.9.3/Module.html#method-i-attr_reader
But why then it is coming as null? Could be related to render json: internals?
这个问题有两个部分。
首先,为什么值(value)不存在?上面已经给出了答案。您的模型掩盖了 ActiveRecord getter 方法
is_read
,指向 ActiveRecord 的内部属性存储,其中一个指向实例变量 @is_read
.因为你没有分配 @is_read
在您的模型中,nil
被退回。其次,为什么是
null
而不是 nil
?正如你所暗示的,这个问题的答案与 render: json
相关。 .在 JSON specification ,您有以下允许的值:string, number, object, array, true, false, null
要生成有效的 JSON 响应,
render: json
替换 Ruby 的 nil
, 使用 JSON 的 null
.那么说你永远不想使用
attr_reader
是否安全? , attr_accessor
等。人。在你的模型中?并不真地。这些可以用作虚拟或 transient 属性,一旦对象被销毁,这些属性就会丢失。但是,应该记住与 ActiveRecord 的交互,以避免遇到看似晦涩难懂的错误。
关于ruby-on-rails - 为什么渲染 json : is returning NULL instead of boolean value,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/29196074/