Handling an ActiveRecord error if database is empty

问题

I'm working on a rails 4 app, and i have the following controller code

 def index
  @issue = Issue.find(1)
  @sections = @issue.sections
  @articles = @issue.articles
 end

which breaks if the database is empty with the error: "Couldn't find Issue with id=1". What is the proper way to check for this in a way that if nothing is in the db it doesn't raise an error?

回答1:

One method you can use is the exists? active record method, like so:

@issue = Issue.where(id: 1)

if @issue.exists?
    # do something if it exists
else
    # do something if it is missing
end

Side note: Since you're attempting to find by id, you don't necessarily need the .where portion; you can simply do: Issue.exists?(1).

exists? documentation on APIDoc

回答2:

In most cases such exception is expected and recommenced. For example, you can rescue it with a custom 404 page.

Anyway, if you really don't want that, you can use find_by method which will output nil if nothing found

@issue = Issue.find_by(id: 1)

回答3:

you can handle that exception in your controller

rescue_from ActiveRecord::RecordNotFound, :with => :record_not_found
def record_not_found
 flash[:alert] = "invalid information"
 redirect_to root_url
end

or you can use a where clause