Ruby: undefined method `find_by_username' - html

Question

I've been following a tutorial Follower Tutorial and I keep getting the error undefined method `find_by_username' for the line.
<%= render '/components/follow_button', :user => User.find_by_username(params[:id]) %>
show.html.erb
<%= render '/components/follow_button', :user => User.find_by_username(params[:id]) %>
<div class="panel panel-default">
<div class="panel-body">
<h5 style="color: grey; font-size: 125%;">Who to follow</h5>
<% for #u in #toFollow do %>
<p style="font-weight: bold; opacity: 0.85;" ><%= #u.username %></p>
<% end %>
</div>
</div>
user.rb
def unfollow(other)
active_relationships.find_by(followed_id: other.id).destroy
_follow_button.html.erb
<% if current_user.id != user.id %>
<div class="panel panel-default">
<div class="panel-body">
<center>
<% if !current_user.following?(user) %>
<%= form_for(current_user.active_relationships.build) do |f| %>
<div><%= hidden_field_tag :followed_id, user.id %></div>
<%= f.submit "Follow", class: "btn btn-primary" %>
<% end %>
<% else %>
<%= form_for(current_user.active_relationships.find_by(followed_id: user.id),
html: { method: :delete }) do |f| %>
<%= f.submit "Unfollow", class: "btn" %>
<% end %>
<% end %>
</center>
</div>
</div>
I've been messing around for ages now and can't work it out. Any help would be appreciated. Feel free to ask for more code etc.

Answer 1

In newer version of rails you should use following code:
Inside controller:
#user = User.find_by(username: username)

Answer 2

In Rails 4 onwards the find_by_... methods are deprecated therefore your User.find_by_username will not work for Rails 4 and higher. You should be able to use either:
User.find(id)
or
User.where(:username=> username)