Answerer's username will not show in Rails? - ruby-on-rails

Question

I am fairly new to Rails 4, and I am creating a Q&A site similar to Stack Overflow.
I have a question page much like the one on Stack Overflow. The question part is working, and then I have answers, which are working too, HOWEVER, I want to be able to have the answerer's name next to their answer.
I am pretty sure I have the controller, model and view set up properly. I have reset the database but it still comes up with errors.
Here's my code:
#Answers_controller.rb create action
def create
#answer = #question.answers.new(answer_params)
#answer.user_id = current_user.username
respond_to do |format|
if #answer.save
format.html { redirect_to [#question], notice: 'Answer was successfully created.' }
format.json { render action: 'show', status: :created, location: #answer }
else
format.html { render action: 'new' }
format.json { render json: #answer.errors, status: :unprocessable_entity }
end
end
end
answer.rb (model):
class Answer < ActiveRecord::Base
belongs_to :user
belongs_to :question
validates :body, presence: true
end
#Then in user.rb I have has_many :answers, has_many :questions
#Also in question.rb has_many :answers
answers/_answer.html.erb:
<%= answer.username %>
<%= answer.body %>
</p>
<p>
<% if current_user.present? && current_user == answer.user %>
<%= link_to 'Delete Answer', [answer.question, answer],
method: :delete,
data: { confirm: 'Are you sure?' } %>
<% end %>
</p>
Then in questions/show:
<div class="container">
<div class="row">
<div class="span8">
<h3><%= #question.title %>
<% if current_user.present? && current_user == #question.user %>
<%= link_to 'Edit', edit_question_path(#question) %></h3>
<% end %>
<hr>
</div>
</div>
<div class="row">
<div class="span8">
<p><%= #question.description %></p>
Asked by <%= #question.user.full_name %>
<hr>
</div>
</div>
<%= render "answers/form" %>
<%= render #question.answers %>
</div>
<script type="text/javascript">
$(document).ready(function(){
$('.wysihtml5').each(function(i, elem) {
$(elem).wysihtml5();
});
})
</script>

Answer 1

It looks like you wrong here
#answer = #question.answers.new(answer_params)
try
#answer = #question.answers.build(answer_params)
Explanaition: you build a new answer but do not refer it to question because according to has_many documentation it has collection.build(attributes = {}, …) not collection.new(attributes).

Answer 2

A couple of things that stand out:
#Answers_controller.rb create action
def create
#answer = #question.answers.new(answer_params)
#answer.user_id = current_user.username # ???? should be current_user.id ????
# omitted
end
answers/_answer.html.erb
<%= answer.username %> # ???? you have no username field on your answer model ???
# ??? should be <%= answer.user.username %> ???
<%= answer.body %>
</p>
# omitted