Setting a variable equal to a function and if statements

Question

I am very new to the Ruby language and Ruby on Rails, so I'm not entirely sure how to word my question (and will probably use incorrect terminology). The following code does not work

@user = User.find_by email: params[:session][:email] 
if @user.authenticate(params[:session][:password]) 
     # Signin @user 
else 
    # Render failed Signin 
end

I get an error that the method authenticate is not defined for nil:Nilclass, but the following code works fine:

@user = User.find_by email: params[:session][:email] 
if @user && @user.authenticate(params[:session][:password]) 
    # Signin @user 
else 
    # Render failed Signin 
end

I don't understand why the first code block doesn't work. When I define @user does the User.find_by method not run and set the value of @user? Or does the variables value get set only when called in the program?

EDIT: unnecessary parentheses removed.

what version of rails are you using?

Said Kaldybaev
– Said Kaldybaev

2013-08-01 06:39:03 +00:00
Commented Aug 1, 2013 at 6:39 — Said Kaldybaev
– Said Kaldybaev, Commented Aug 1, 2013 at 6:39

PericlesTheo · Accepted Answer · 2013-08-01 06:51:47Z

3

Here's what I think is wrong with the first block:

In the first block, you search for a user and if not found will return nil. Then, you are trying to authenticate nil and that's why is giving you a not defined for Nil:class.

On the second block you are fixing the problem by adding the @user in your if block. Testing to see whether you actually have a retrieved user first, incase the user is not found the block will not be executed.

answered Aug 1, 2013 at 6:51

PericlesTheo

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2 Comments

Jason Lowry Over a year ago

Thank you! This makes sense to me. I've spent the last two hours googling the issue and couldn't find anything. I tried upvoting your answer, but apparently I don't have enough reputation to do that yet.

PericlesTheo Over a year ago

Np, if you think this is the correct answer just mark it as such.

dax · Accepted Answer · 2013-08-01 06:40:24Z

0

To start, here's a good breakdown of the && operator - what it does and doesn't do.

in your first block, in the second line:

if (@user.authenticate(params[:session][:password]))

you don't need parentheses around @user -

if @user.authenticate(params[:session][:password])

You should also be using find_by_email as Hassan has pointed out.

answered Aug 1, 2013 at 6:40

dax

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2 Comments

Jason Lowry Over a year ago

Thanks, I have removed the unnecessary parentheses, but from what I've read is find_by preferred over find_by_email in Rails 4.0?

dax Over a year ago

ah, okay, sorry didn't realize you were using rails 4.0!

Hassan Javeed · Accepted Answer · 2013-08-01 06:59:13Z

0

The find_by method you used should result in a NoMethodError exception(unless you have defined that method in the User model).

You can use a dynamic finder method(http://guides.rubyonrails.org/active_record_querying.html#dynamic-finders) on any of the user's attributes like

User.find_by_email(params[:session][:email])

UPDATE: I was thinking of Rails 3 when posting the answer, Rails 4 removes dynamic finders, and the method you are using is perfectly valid.

edited Aug 1, 2013 at 6:59

answered Aug 1, 2013 at 6:38

Hassan Javeed

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1 Comment

Said Kaldybaev Over a year ago

before posting such answer, you'd better know what version of rails @Jason using. In Rails 4, there is find_by(*args) method

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