at I2 I get undefined method when I type a.comments in command.

[darlingtonp4]

I get
2.3.4 :001 > a = Article.first
Article Load (0.2ms) SELECT "articles".* FROM "articles" ORDER BY "articles"."id" ASC LIMIT ? [["LIMIT", 1]]
=> nil
2.3.4 :002 > a.comments
NoMethodError: undefined method `comments' for nil:NilClass
from (irb):2
I don't know if this has to do with models generated being different from the ones shown in the site but I tried both ways and keep getting the same problem.

[iandouglas]

a = Article.first
# this returned 'nil', there was no article returned from the database
a.comments
# this throws an error because there's no "comments" method (or database association) 
# on the 'nil' that was returned and stored in your 'a' variable.