Why can't I access this field? (Rails 3)

I really can't figure out why I can't access the user_id field for the class Post. I have it as a field in my database (I can see it, and it isn't blank. Yet for some reason, I'm getting this error:

undefined method `user_id' for #<Class:0x103497448>
Extracted source (around line #10):

7:   <h2>Topics</h2>
8:   <% @board.topics.each do |topic| %>
9:     <% @post = topic.posts(1) %>
10:     <b><%= User.find(@post.user_id).username %> says <%= link_to topic.subject,      [@board, top开发者_开发百科ic] %></b><br />
11:   <% end %>
12: <% end %>
13: 

topic.posts(1) will return an array. Hence #<Class:0x103497448>

The right way to get the first post for a topic would be

9:     <% @post = topic.posts.first %>
10:     <b><%= User.find(@post.user_id).username %> says <%= link_to topic.subject,      [@board, topic] %></b><br />

Try <% @post = topic.posts.limit(1) %>