Inexplicable unpermitted parameters error in Rails 4 nested form - ruby-on-rails-4

Question

I've searched high and low, and found many posts similiar, but can't seem to debug the following code.
I have a project model, which has many many teams. It has many users through teams. Here are the relevant models.
project.rb
class Project < ActiveRecord::Base
has_many :teams
has_many :users, :through => :teams
accepts_nested_attributes_for :teams
end
team.rb
class Team < ActiveRecord::Base
belongs_to :project
belongs_to :user
end
user.rb
class User < ActiveRecord::Base
has_many :teams
has_many :projects, :through => :teams
end
projects_controller.rb
class ProjectsController < ApplicationController
def index
#projects = Project.all
end
def new
#project = Project.new
end
def create
#project = Project.create(project_params)
redirect_to projects_url
end
def show
#project = Project.find(params[:id])
end
def edit
#project = Project.find(params[:id])
end
def update
#project = Project.find(params[:id])
#project.update(type_params)
redirect_to project_url
end
def destroy
#project = Project.find(params[:id])
#project.destroy
redirect_to projects_url
end
end
private
def project_params
params.require(:project)
project_params = params.require(:project).
permit(:name, :code, :description, :externalId,
{:teams_attributes => [:id, :userId, :projectId]})
end
I have a nested form, that should allow me to create a new project and one team (just typing in the ID), however I get an unpermitted parameters exception ("Unpermitted parameters: team")
Whenever I submit the form. Form code is below.
new.html.erb
<h1>Create New Project</h1>
<%=form_for(#project) do |f| %>
<p>
<%=f.label "Name"%>
<%=f.text_field :name%> <br>
<%=f.label "Code"%>
<%=f.text_field :code%> <br>
<%=f.label "External ID"%>
<%=f.text_field :externalId%> <br>
<%=f.label "Description"%>
<%=f.text_field :description%> <br>
</p>
<ul>
<%= f.fields_for :team do |tf| %>
<li>
<%= tf.label 'User Id' %>
<%= tf.text_field :userId %>
<%= tf.label 'Project Id' %>
<%= tf.text_field :projectId %>
</li>
</ul>
<%end%>
<%=f.submit%>
<%end%>
I've paid special attention to the permitted parameters fields, and think I got them right, but, rails disagrees.
Any help would be appreciated

Answer 1

Your nested form doesn't work with has_many because it is singluar. You want to use f.fields_for :teams do instead (plural). Please try the following changes:
project_controller.rb
def new
#project = Project.new
#project.teams.build
end
[...]
private
[...]
# Never trust parameters from the scary internet, only allow the white list through.
def project_params
params.require(:project).permit(:name, :code, :externalId, :description, teams_attributes: [ :user_id, :project_id ])
end
new.html.erb
<h1>Create New Project</h1>
<%=form_for(#project) do |f| %>
<p>
<%=f.label "Name"%>
<%=f.text_field :name%> <br>
<%=f.label "Code"%>
<%=f.text_field :code%> <br>
<%=f.label "External ID"%>
<%=f.text_field :externalId%> <br>
<%=f.label "Description"%>
<%=f.text_field :description%> <br>
</p>
<ul>
<%= f.fields_for :teams do |tf| %>
<li>
<%= tf.label 'User Id' %>
<%= tf.text_field :user_id %>
<%= tf.label 'Project Id' %>
<%= tf.text_field :project_id %>
</li>
<%end%>
</ul>
<%=f.submit%>
<%end%>

Answer 2

Change this method like this and try
private
def project_params
params.require(:project)
project_params = params.require(:project).
permit(:name, :code, :description, :externalId,
{:teams_attributes => [:id, :userId, :projectId]})
end
to
private
def project_params
params[:project].permit(:name, :code, :description, :externalId,
{:teams_attributes => [:id, :userId, :projectId]})
end