Simple Form for - Nested Resources paths - ruby-on-rails

Question

I'm trying to make an app in Rails 5 for post answer to the task.
The Task content and the answer form in the same page.
When the user come into the task page, he can see the task content.
And he can post(create) an answer or edit the answer.
I get an error:
NoMethodError in Tasks#show
undefined method `to_key' for #
Did you mean? to_query
to_set
to_ary
What am I doing wrong?
What else information do you need that can help debug this issue?
I'd really apprieciate any help!
Models
```
# task.rb
class Task < ApplicationRecord
belongs_to :post
has_many :answers, dependent: :destroy
end
# answer.rb
class Answer < ApplicationRecord
belongs_to :task
belongs_to :user
end
```
routes.rb
```
resources :tasks, only: [:show] do
resources :answers #, only: [:new, :create, :edit, :update]
end
```
Controllers
```
# tasks_controller.rb
class TasksController < ApplicationController
before_action :authenticate_user!, only: [:show]
def show
#task = Task.find(params[:id])
#post = #task.post
if #task.answers.present?
#answer = Answer.where("task_id = ? and user_id = ?", #task.id, current_user.id)
else
#answer = Answer.new
end
end
end
# answers_controller.rb
def new
#task = Task.find(params[:task_id])
#answer = Answer.new
end
def create
#task = Task.find(params[:task_id])
#answer = Answer.new(answer_params)
#answer.task_id = #task.id
#answer.user_id = current_user.id
if #answer.save
redirect_to post_path(#task.post), notice: "Answer Added."
else
render :new
end
end
```
Views
```
<div class="answer-form">
<%= simple_form_for [#task, #answer], :url => task_answer_path(#task, #answer), method: :put do |f| %>
<% if #task.answers.present? %>
<%= f.input :content, id: "x", value: #task.answers.first.content,
input_html: {class: "hidden"}, name: "content", label: false %>
<trix-editor input="x" class="formatted_content trix-content"></trix-editor>
<div class="form-actions">
<%= f.submit "Submitting", class: "assignment-btn", data: {disable_with: "Submitting..."} %>
</div>
<% end %>
<% else %>
<%= simple_form_for [#task, #answer], :url => task_answers_path(#task), method: :post do |f| %>
<%= f.input :content, id: "x", value: "content",
input_html: {class: "hidden"}, name: "content", label: false %>
<trix-editor input="x" class="formatted_content trix-content"></trix-editor>
<div class="file-upload-block">
<input name="fileToUpload[]" id="fileToUpload" type="file">
</div>
<div class="form-actions">
<%= f.submit "提交", class: "assignment-btn", data: {disable_with: "Submitting..."} %>
</div>
<% end %>
<% end %>
</div>
```

Answer 1

I know what may be wrong, the line below was returning an ActiveRecord::Relation, not the instance itself, you need to append 'first' in the end of the answer query, like such:
#answer = Answer.where(task: #task, user: current_user).first