Whats a good way to avoid nil lookup errors

Rails
1

When navigating to: http://localhost:3000/users/12

Whats a good way of avoiding the error: “Couldn’t find User with
ID=12”, which happens when i try to display a page of user_id 12 that
doesnt exist in the database.

Instead of showing the error. id like to show a page that says: “This
user does not exist”

Someone suggested using rescue_from. Is this the best solution for
this? Or are there better alternative approaches?

2

def show
@user = User.find(params[:id])
rescue ActiveRecord::RecordNotFound
redirect_to users_path, :alert => “This user does not exists”
end

3

One of the solutions would be to use redirect_to and flash[:notice]
like:

@user = User.find(1)
unless @user
flash[:notice] = “can’t find user with given id”
redirect_to users_path
end

I won’t say it’s the best but it’s still a solution :slight_smile:

On 5 sept., 13:55, Christian F. [email protected]

4

Hi Paul. but wouldnt that redirect to users_path on any activerecord
not found event?

5

Yes but, it will never reach “unless.” The system fails after @user =
User.find(1) since Active Record is trying to find a record that does
not exists

6

@user = User.find(1) if User.exists?(1)

I don’t like doing two lookups for one record, but it works

7

What about
@user = User.find(:first, :conditions => {:id => 1})
if (@user)
blah, blah, blah
end

It’s longer to type, but returns nil if the user doesn’t exist.

On Sun, 05 Sep 2010 21:21:25 +0800, Michael P. [email protected]

8

nope, only within the action.

On Sep 5, 11:31 pm, Christian F. [email protected]

9

On Sep 5, 2010, at 9:30 AM, Simon M. wrote:

On Sun, 05 Sep 2010 21:21:25 +0800, Michael P.
[email protected] wrote:

@user = User.find(1) if User.exists?(1)

I don’t like doing two lookups for one record, but it works

What about
@user = User.find(:first, :conditions => {:id => 1})
if (@user)
blah, blah, blah
end

It’s longer to type, but returns nil if the user doesn’t exist.

Ugis almost has it. Try this

@user = User.find_by_id(1)
unless @user
flash[:notice] = “can’t find user with given id”
redirect_to users_path
end

ActiveRecord::Base#find_by_id is a dynamic finder that will work just
like the line Simon has above–nil if there is no record found.

-Rob

Rob B.
[email protected] http://AgileConsultingLLC.com/
[email protected] http://GaslightSoftware.com/

10

Good call on that find_by_id. Noted to myself :slight_smile:

11

Hi Christian

On Sun, Sep 5, 2010 at 9:38 AM, Christian F.
[email protected] wrote:

So this would be the convention right? not by using rescue_from. Is
this right?

Yes. When possible, avoid begin-rescue by using Ruby / Rails to
return a value you can handle within the normal course of your
application logic. It makes for more readable code.

Best regards,
Bill

12

So this would be the convention right? not by using rescue_from. Is
this right?