Help with ruby query!

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

I think you can find that answer here:

http://railscasts.com/episodes/3-find-through-association

Also http://guides.rails.info/finders.html

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

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:

<% @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 %>

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:

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)

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.