Help with ruby query!

rubyonrails-talk
1

I am using Rails 2.0.2 with mysql database

I have two tables: book and author Table book has 3 columns: id, isbn, and title Table author has 3 columns: id, name, and age

In the models I have: class Book < ActiveRecord::Base belongs_to :author end

class Author < ActiveRecord::Base    has_many :books end

I have author_id as the foreign key in the book's table

The user will select 'age' from a list Then I want to display names of all authors with the selected age, and also the 'title' from book's table.

In plain SQL, the query will be like this:

SELECT name, title FROM author INNER JOIN book ON author.id = book.id WHERE age = "the selected age"

How can I write this in Ruby?

Thanks Cypray

2

I think you can find that answer here:

3

Also rails.info

4

class Author < ActiveRecord::Base   has_many :books

def author_age    Author.find :all, (:conditions => ["age = ?", params[:authors]])    end

end

What I want to do is to display all author's name base on the selected age.

please, What is wrong with my query?

because hashes are written with {} not () (and in fact you don't even
need the {} here)

Fred

5

Thanks a lot Mr. Fred.

Now, I am having trouble with displaying the query result on authors\show.html I am having problems referencing the returned object and getting the two columns displayed. The error is: "You have a nil object when you didn't expect it!"

I have this in my model: class Author < ActiveRecord::Base

has_many :books

def author_age     @results = Author.find :all, :conditions => ["age = ?", params[:authors]]      end end

I have this on view\authors\show.html

<table border="1"> <tr> <td width="20%"><p align="center"><i><b>Author Name</b></i></td> <td width="20%"><p align="center"><i><b>Age</b></i></td> </tr>

<% @results.each do |result| %> // I am not sure if this is right!

<tr>

<td><%=h @result.name %></td> <td><%=h @result.age %></td> </tr>

</table>

What I want to do is to display the 'name' and 'age' that the query returned.

Please help! Cypray

Frederick Cheung wrote:

6

<% @results.each do |result| %> // I am not sure if this is right!

<tr>

<td><%=h @result.name %></td> <td><%=h @result.age %></td> </tr>

should be

<% @results.each do |result| %> // I am not sure if this is right!

<tr>

<td><%=h result.name %></td> <td><%=h result.age %></td> </tr> <% end %>

7

I made those changes, but I am still getting this error: "You have a nil object when you didn't expect it!"

It is pointing to the line with the loop: <% @results.each do |result|

My model look like this:

class Author < ActiveRecord::Base

has_many :books

def author_age     @results = Author.find :all, :conditions => ["age = ?", params[:authors]]      end end

I have this in view\authors\show.html

<tr> <td width="20%"><p align="center"><i><b>Author Name</b></i></td> <td width="20%"><p align="center"><i><b>Age</b></i></td> </tr>

<% @results.each do |result| %> // It is flagging this line.

<tr>

<td><%=h result.name %></td> <td><%=h result.age %></td> </tr> <% end %>

Is something wrong with the private method in the model or something else? Please help. Cypray

Thorsten Mueller wrote:

8

It is pointing to the line with the loop: <% @results.each do |result|

So for one reason or another @results is nil Most likely your query doesn't return any records. (btw: you better name that @authors instead of @results for readablity)

So what is in params[:authors] ? Where does this param come from and does it contain an age? After all, that's what you ask Rails to search for in @results = Author.find :all, :conditions => ["age = ?", params [:authors]]

So if for example params[:authors] would contain an authors id or name (as the name suggests) then it wouldn't find anything.

You could easily debug this with something like: @results = Author.find :all, :conditions => ["age = ?", params [:authors]] logger.info "RESULT: #{@results.size}" Then you would find the number of found records in development.log (Where btw you could see, which params where sent to your controller)

9

The problem could be the query because when I search for one record, it works.

In SQL, the query will be: SELECT name, age FROM authors WHERE age = 'the selected age' // the value, not the id of the selected age.

So answer the previous question:

Thorsten Mueller wrote:

So what is in params[:authors] ? Where does this param come from and does it contain an age?

You can look in your logs (Rails and/or MySQL) to see the query that's being constructed from your code, if nothing else.