2005 Mar 03

Rails Best Practices

I've been knee deep in rails for about five weeks or so. I've found it to be a rather powerful framework. However, it's simplicity makes it very easy to write inefficient database code.

In ASP.Net for example, if I want to load a list of issues, with their related comic books and publishers, I perform a single JOIN query and fill some objects.

In Rails, the code for setting up related objects is vastly simplified. However, there's really no way to load multiple objects in a single query. So, the simple way is to do something like this:

In the controller:

@issues = Issue.find_all

In the view:


<% @issues.each do issue %>

<%=issue.comic.name%> #<%=issue.number%>

<% end %>

This would give a list of issues with their comic title next to it. The problem is, issue.comic is asking the DB for the data each time, even if that comic has already been loaded. This executes n + 1 queries.

"Scott":http://scott.elitists.net suggested creating a small lookup hash:


<% 
comics = Comic.find_all.inject({}) do |hsh, c|
  hsh.merge({c.id=>c})
end
@issues.each do issue %>

<%=comics[issue.comic_id]%> #<%=issue.number%>

<% end %>

This executes only 2 queries, so you're not pounding the database everytime the page is recached.

Any thoughts?