Update:

This issue was not properly explored. The real issue lies within render :json.

这个问题没有得到适当的探讨。真正的问题在于呈现:json。

The first code paste in the original question will yield the expected result. However, there is still a caveat. See this example:

原始问题中的第一个代码粘贴将产生预期的结果。然而，仍有一个警告。看这个例子:

render :json => current_user

呈现:json = > current_user

is NOT the same as

不一样吗

render :json => current_user.to_json

呈现:json = > current_user.to_json

That is, render :json will not automatically call the to_json method associated with the User object. In fact, if to_json is being overridden on the User model, render :json => @user will generate the ArgumentError described below.

也就是说，render:json不会自动调用与User对象关联的to_json方法。实际上，如果用户模型上覆盖了to_json，那么呈现:json => @user将生成下面描述的ArgumentError。

summary

# works if User#to_json is not overridden
render :json => current_user

# If User#to_json is overridden, User requires explicit call
render :json => current_user.to_json

This all seems silly to me. This seems to be telling me that render is not actually calling Model#to_json when type :json is specified. Can someone explain what's really going on here?

这一切在我看来都是愚蠢的。这似乎在告诉我，当类型:json被指定时，渲染实际上并没有调用Model#to_json。有人能解释一下这里到底发生了什么吗?

Any genii that can help me with this can likely answer my other question: How to build a JSON response by combining @foo.to_json(options) and @bars.to_json(options) in Rails

任何能帮助我实现这一点的genii都可以回答我的另一个问题:如何通过在Rails中结合@foo.to_json(options)和@bars.to_json(options)来构建JSON响应

Original Question:

I've seen some other examples on SO, but I none do what I'm looking for.

我见过其他的例子，但是我没有做我想做的。

I'm trying:

我尝试:

class User < ActiveRecord::Base

  # this actually works! (see update summary above)
  def to_json
    super(:only => :username, :methods => [:foo, :bar])
  end

end

I'm getting ArgumentError: wrong number of arguments (1 for 0) in

我得到了ArgumentError:错误的参数数(1代表0)

/usr/lib/ruby/gems/1.9.1/gems/activesupport-2.3.5/lib/active_support/json/encoders/object.rb:4:in `to_json

Any ideas?

什么好主意吗?

4 个解决方案

#1

203

You are getting ArgumentError: wrong number of arguments (1 for 0) because to_json needs to be overridden with one parameter, the options hash.

您将得到ArgumentError:错误的参数数(1代表0)，因为to_json需要使用一个参数，即options散列重写。

def to_json(options)
  ...
end

Longer explanation of to_json, as_json, and rendering:

to_json、as_json和呈现的更详细解释:

In ActiveSupport 2.3.3, as_json was added to address issues like the one you have encountered. The creation of the json should be separate from the rendering of the json.

在ActiveSupport 2.3.3中，添加了as_json以解决您遇到的问题。json的创建应该与json的呈现分开。

Now, anytime to_json is called on an object, as_json is invoked to create the data structure, and then that hash is encoded as a JSON string using ActiveSupport::json.encode. This happens for all types: object, numeric, date, string, etc (see the ActiveSupport code).

现在，无论何时调用对象to_json，都会调用as_json来创建数据结构，然后使用ActiveSupport:: JSON .encode将该散列编码为JSON字符串。这适用于所有类型:对象、数字、日期、字符串等(参见ActiveSupport代码)。

ActiveRecord objects behave the same way. There is a default as_json implementation that creates a hash that includes all the model's attributes. You should override as_json in your Model to create the JSON structure you want. as_json, just like the old to_json, takes an option hash where you can specify attributes and methods to include declaratively.

ActiveRecord对象的行为是相同的。有一个默认的as_json实现，它创建一个包含模型所有属性的散列。您应该在模型中覆盖as_json，以创建您想要的JSON结构。as_json，就像旧的to_json一样，采用一个选项哈希，您可以在其中指定属性和方法以声明的方式包含。

def as_json(options)
  # this example ignores the user's options
  super(:only => [:email, :handle])
end

In your controller, render :json => o can accept a string or an object. If it's a string, it's passed through as the response body, if it's an object, to_json is called, which triggers as_json as explained above.

在控制器中，render:json => o可以接受字符串或对象。如果它是一个字符串，它将作为响应主体传递，如果它是一个对象，则调用to_json，它将触发如上所述的as_json。

So, as long as your models are properly represented with as_json overrides (or not), your controller code to display one model should look like this:

因此，只要您的模型用as_json重写(或不使用as_json重写)恰当地表示，那么显示一个模型的控制器代码应该如下所示:

format.json { render :json => @user }

The moral of the story is: Avoid calling to_json directly, allow render to do that for you. If you need to tweak the JSON output, call as_json.

这个故事的寓意是:避免直接调用to_json，允许渲染为您这样做。如果需要调整JSON输出，请调用as_json。

format.json { render :json => 
    @user.as_json(:only => [:username], :methods => [:avatar]) }

#2

If you're having issues with this in Rails 3, override serializable_hash instead of as_json. This will get your XML formatting for free too :)

如果您在Rails 3中遇到这个问题，请重写serizabalile_hash而不是as_json。这将使您的XML格式得到*:)

This took me forever to figure out. Hope that helps someone.

我花了很长时间才弄明白。希望可以帮助别人。

#3

For people who don't want to ignore users options but also add their's:

对于那些不想忽略用户选项，但也想添加自己的选项的人:

def as_json(options)
  # this example DOES NOT ignore the user's options
  super({:only => [:email, :handle]}.merge(options))
end

Hope this helps anyone :)

希望这对任何人都有帮助。

#4

Override not to_json, but as_json. And from as_json call what you want:

重写不是to_json，而是as_json。从as_json调用你想要的:

Try this:

试试这个:

def as_json 
 { :username => username, :foo => foo, :bar => bar }
end

#1

203