如果数据库中不存在 params[:id]，我应该如何编写代码

Question

I'm writing a show action in a controller and want to branch if no id received from params[:id] exists in my database.

My app is still being created. I've tried conditional branching and exception handling. However, they didn't work as expected.

class ArticlesController < ApplicationController

  #...

  def show
    begin
      @article = Article.find(params[:id])
    rescue
      render root
    end
  end

  #...

end

I expect to be redirect to the root if any error occurs.

The above code returns the record if it is found successfully. However, an ActiveRecord::RecordNotFound in ArticlesController#show occurs if no record is found.

How should I write code for this error?

Answer 1

How should I write code for this error?

The short answer is "you shouldn't".

Exceptions should, IMO, be exceptional. It sounds like you might expect this circumstance, so I suggest you write code that handles the scenario without raising an exception.

If you really think you'll have circumstances where the Article record does not exist for the given params[:id] (seems a little odd, but I guess it's possible), then I would suggest that you use .find_by instead of .find :

class ArticlesController < ApplicationController

  #...

  def show
    if @article = Article.find_by(id: params[:id])
      # do something with the article 
    else
      render root
    end
  end

  #...

end

It seems like to you might want to do a redirect instead of a render :

class ArticlesController < ApplicationController

  #...

  def show
    if @article = Article.find_by(id: params[:id])
      # do something with the article 
    else
      redirect_to root_path
    end
  end

  #...

end

But, maybe not...

Also, rescuing everything like this:

def show
  begin
    @article = Article.find(params[:id])
  rescue
    render root
  end
end

...is generally viewed as code smell. There are a lot of articles on the interwebs about why.

Answer 2

You can handle the exception from ArticlesController but I advise put the code at ApplicationController like this:

rescue_from ActiveRecord::RecordNotFound do
   redirect_back fallback_location: root_path, alert: t("resource_not_found")
end

Answer 3

Maybe You can code like this:

 def show
    @article = Article.find_by(id: params[:id])
    unless @article.present?
      flash[:error] = "Not Found."
      redirect_to root_path
    end
  end

Answer 4

why write so much code, while you can achieve with two lines only.

class ArticlesController < ApplicationController
  def show
    @article = Article.find_by(id: params[:id])
    redirect_to root_path unless @article.present?
  end 
end 

Answer 5

Your code should be written like this:

 def show
    begin
      @article = Article.find(params[:id])
    rescue
      redirect_to root_path
    end
 end