Rails 5:无法从参数中检索哈希值 [英] Rails 5: unable to retrieve hash values from parameter

问题描述

我遇到了一个奇怪的问题.

I'm running into a strange issue.

undefined method `values' for #<ActionController::Parameters:0x007fb06f6b2728>

是我得到的错误，当我将一个变量分配给一个 param 散列并尝试获取它的值时.

is the error I get, when I assign a variable to a param hash, and try to get it's values.

attributes = params[:line_item][:line_item_attributes_attributes] || {}
attributes.values

参数看起来像这样一个散列的散列:

the parameter looks like this a hash of hashes:

{"0"=>{"product_attribute_id"=>"4"}, "1"=>{"product_attribute_id"=>"7"}}

现在，当我在控制台中执行此操作并将其分配给变量属性时，它可以完美地工作.所以我很难理解什么在这里不起作用 - 以及如何使它起作用.

now when I do this in console and assign that to a variable attributes it works flawlessly. So I'm struggling to understand what isn't working here - and how to make it work.

推荐答案

看看 这个.很奇怪，因为 ActionController::Parameters 是 Hash 的子类，你可以转换它 直接 使用 to_h 方法对 params 散列进行散列.

take a look to this. Very weird since ActionController::Parameters is a subclass of Hash, you can convert it directly to a hash using the to_h method on the params hash.

但是 to_h 仅适用于白名单参数，因此您可以执行以下操作:

However to_h only will work with whitelisted params, so you can do something like:

permitted = params.require(:line_item).permit(: line_item_attributes_attributes)
attributes = permitted.to_h || {}
attributes.values

但如果您不想加入白名单，那么您只需要使用 to_unsafe_h 方法即可.

But if instead you do not want to whitelist then you just need to use the to_unsafe_h method.

我对这个问题很好奇，所以我开始研究，现在你澄清你使用的是 Rails 5，这就是这个问题的原因，正如@tillmo 在稳定版本的 Rails 4.x 中所说的那样，ActionController::Parameters 是 Hash 的子类，因此它确实应该响应 values 方法，但是在 Rails 5 ActionController::Parameters 现在返回一个 Object 而不是 Hash

I was very curious about this issue, so I started researching, and now that you clarified that you are using Rails 5, well that's the cause of this issue, as @tillmo said in stable releases of Rails like 4.x, ActionController::Parameters is a subclass of Hash, so it should indeed respond to the values method, however in Rails 5 ActionController::Parameters now returns an Object instead of a Hash

注意:这不会影响访问 params 散列中的键，如 params[:id].您可以查看实施此更改的拉取请求.

Note: this doesn’t affect accessing the keys in the params hash like params[:id]. You can view the Pull Request that implemented this change.

要访问对象中的参数，您可以将 to_h 添加到参数中:

To access the parameters in the object you can add to_h to the parameters:

params.to_h

如果我们查看 ActionController::Parameters 中的 to_h 方法，我们可以看到它在将参数转换为散列之前检查参数是否被允许.

If we look at the to_h method in ActionController::Parameters we can see it checks if the parameters are permitted before converting them to a hash.

# actionpack/lib/action_controller/metal/strong_parameters.rb
def to_h
  if permitted?
    @parameters.to_h
  else
    slice(*self.class.always_permitted_parameters).permit!.to_h
  end
end

例如:

def do_something_with_params
  params.slice(:param_1, :param_2)
end

哪个会返回:

{ :param_1 => "a", :param_2 => "2" }

但现在这将返回一个 ActionController::Parameters 对象.

But now that will return an ActionController::Parameters object.

对此调用 to_h 会返回一个空的哈希值，因为 param_1 和 param_2 是不允许的.

Calling to_h on this would return an empty hash because param_1 and param_2 aren’t permitted.

要从ActionController::Parameters 访问参数，您需要先允许参数，然后在对象上调用to_h

To get access to the params from ActionController::Parameters, you need to first permit the params and then call to_h on the object

def do_something_with_params
  params.permit([:param_1, :param_2]).to_h
end

以上将返回一个包含您刚刚允许的参数的哈希值，但如果您不想允许参数并想跳过该步骤，则还有另一种使用 to_unsafe_hash 方法的方法:

The above would return a hash with the params you just permitted, but if you do not want to permit the params and want to skip that step there is another way using to_unsafe_hash method:

def do_something_with_params
  params.to_unsafe_h.slice(:param_1, :param_2)
end

有一种方法可以始终允许来自 application.rb 的配置中的参数，如果您想始终允许某些参数，您可以设置一个配置选项.注意:这将返回带有字符串键的哈希值，而不是符号键.

There is a way of always permit the params from a configuration from application.rb, if you want to always allow certain parameters you can set a configuration option. Note: this will return the hash with string keys, not symbol keys.

#controller and action are parameters that are always permitter by default, but you need to add it in this config.
config.always_permitted_parameters = %w( controller action param_1 param_2)

现在您可以访问以下参数:

Now you can access the params like:

def do_something_with_params
  params.slice("param_1", "param_2").to_h
end

注意现在键是字符串而不是符号.

Note that now the keys are strings and not symbols.

希望这有助于您了解问题的根源.

Hope this helps you to understand the root of your issue.

来源:eileen.codes

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