title: Error: undefined function user/2 when running mix phoenix.server
body: <p>I created this module:</p>
  
  <pre><code>defmodule Discuss.Topic do
      user Discuss.Web, :model
  
      schema "topics" do
          field :title, :string
      end
  
      def changeset(struct, params \\ %{}) do
          struct
          |&gt; cast(params, [:title])
          |&gt; validate_required([:title])
      end
  end
  </code></pre>
  
  <p>and I got this error when using <code>mix phoenix.server</code></p>
  
  <pre><code>== Compilation error in file web/models/topic.ex ==
  ** (CompileError) web/models/topic.ex:2: undefined function user/2
      (stdlib) erl_eval.erl:680: :erl_eval.do_apply/6
      (elixir) lib/kernel/parallel_compiler.ex:229: anonymous fn/4 in Kernel.ParallelCompiler.spawn_workers/7
  </code></pre>
  
  <p>Any idea of what's happening? I'm new to Phoenix and Elixir.</p>