question about find_by


i am new to ruby/rails, and i am struggling with the find_by method. Heres some background on what i am trying to get done:

I have a User object, and a Book. User has_one Book, and Book belongs_to User.

basically, i have a combo box which displays all the books, i get the id the book is stored in, from the form and then in the user model class, i try and find the according and assign the according book, with this find method: = Book.find_by_id(b_id)

unfortunately i end up with this error:

Mysql::Error: #42S22Unknown column 'books.user_id' in 'where clause': SELECT * FROM books WHERE (books.user_id = 1) LIMIT 1

I dont understand why it is searching the user_id column (which doesnt exist), rather than id ....

At first, i thought something was wrong with my Book.find_by statement, but i tried the same line in an ActionMailer, and it worked fine.

can someone please clear this up?


My guess is that it's because you are using self in the User class.


@book = Book.find_by_id(b_id)

My guess is that the associations are set up wrong. If a User has_one Book then it will indeed assume there's a user_id column on books. It may seem slightly unintuitive, but you may want to swap it around - a User belongs_to a Book, if you have a book_id column on the users table, and a Book has_one (or has_many) User(s).

Hi Gabriel,

you guessed right...that was my does seem counter intuitive, but my user has the book id, and my books do not has a user_id, since a book can belong to many users.

but it still isnt working, this line seems to fail in my rhtml file:

Book: <%= %>

can i not access relationships this way?

Unless you've defined a to_s method on Book, you want to call the explicit attribute you wish to display the value of - like or for example.

i actually copied the wrong thing. i originally had what you suggested, but it was failing...after snoopin around a bit...i realized i accidentally deleted the 'end' at the end of my Book class....stupid vi....