Updating multiple models with one form in Rails - ruby-on-rails

Question

I am new to Rails and trying to build a form that allows users to complete and submit a form. The form completes their profile. I want the form to update the Users model (and database table) as well as the Interests model (hobbies). I am using a form with fields_for.
However submitting the form does not update the Interests model. It either only updates the User model or returns various errors (the following produces Interest user must exist error):
MODELS:
class User < ApplicationRecord
has_many :interests, foreign_key: "interests_user_id"
accepts_nested_attributes_for :interests
end
class Interest < ApplicationRecord
belongs_to :user
self.primary_key = "interest_id"
end
CONTROLLER:
class UsersController < ApplicationController
def index
#allUsers = User.all
end
def new
#user = User.new
#user.interests.build
end
def create
#user = User.new permitted_params
=begin
#user = User.new(
:author => params[:user][:author],
:user_name => params[:user][:user_name],
:user_bio => params[:user][:user_bio],
)
#user.interests.new(
:interest_name => params[:user][:interests_attributes][:interest_name],
:interest_experience_level => params[:user][:interests_attributes][:interest_experience_level],
:interest_positon => params[:user][:interests_attributes][:interest_positon],
)
=end
if #user.save
redirect_to users_url
else
render 'new'
end
end
private
def permitted_params
#params.require(:interest).permit(User.attribute_names.map(&:to_sym),interest.attribute_names.map(&:to_sym))
params.require(:user).permit(User.attribute_names.map(&:to_sym), interests_attributes: [:interest_name,:interest_experience_level,:interest_positon])
end
end
FORM:
<%= form_with model: #user do |newUser| %>
<% if #user.errors.any? %>
<ul>
<% #user.errors.full_messages.each do |message| %>
<li> <%= message %></li>
<%end%>
</ul>
<%end%>
<div class="form-sections" id="user-profile">
<h3>General Information</h3>
<table class="formTables" id="formMainInfo">
<%= newUser.hidden_field :author, value:1 %>
<tr class="formRows">
<td class="formDescriptionCol"><%= newUser.label :user_name, "Your Name" %></td>
<td class="formInputCol">
<%= newUser.text_field :user_name %>
</td>
</tr>
<tr class="formRows">
<td class="formDescriptionCol"> <%= newUser.label :user_bio, "Biography" %></td>
<td class="formInputCol">
<%= newUser.text_area :user_bio %>
</td>
</tr>
<h3>Interests</h3>
<%= newUser.fields_for :interests do |newInterest| %>
<tr class="interestRows">
<td >Interest Name:</td>
<td>
<%= newInterest.text_field :interest_name%>
</td>
</tr>
<tr class="interestRows">
<td ><%=newInterest.label :interest_experience_level, "Experience Level" %></td>
<td >
<%= newInterest.text_field :interest_experience_level %>
</td>
</tr>
<tr class="interestRows">
<td ><%= newInterest.label :interest_position, "Position" %></td>
<td >
<%= newInterest.text_field :interest_position %>
</td>
</tr>
<%end%>
</table>
</div>
<div class="formSections" id="buttonsSection">
<%= newUser.submit "submit" %>
</div>
<%end%>
SCHEMA:
create_table "interests", primary_key: "interest_id", id: :integer, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8" do |t|
t.integer "interest_user_id", null: false
t.string "interest_name", limit: 45, null: false
t.string "interest_experience_level", limit: 45, null: false
t.string "interest_position", limit: 45, null: false
t.index ["interest_user_id"], name: "user_id_idx"
end
create_table "users", primary_key: "user_id", id: :integer, force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8" do |t|
t.string "user_name", limit: 60, null: false
t.string "author", limit: 60, null: false
t.string "user_bio", limit: 500, null: false
end
add_foreign_key "interests", "users", column: "interest_user_id", primary_key: "user_id", name: "interest_user_name", on_update: :cascade, on_delete: :cascade