Comment delete ActionView::Template::Error (undefined method `each' for nil:NilClass):

Question

I get 500 error when trying to delete a comment. On the backend the comment is deleted, but it errors out with ActionView::Template::Error (undefined method `each' for nil:NilClass): even though @comments should be populated. I used window.location.reload() and that works just fine. Any ideas how to remedy this?

log

Started DELETE "/api/comments/51" for ::1 at 2020-07-25 11:48:17 -0400
Processing by Api::CommentsController#destroy as JSON
  Parameters: {"id"=>"51"}
  Comment Load (0.6ms)  SELECT  "comments".* FROM "comments" WHERE "comments"."id" = $1 LIMIT $2  [["id", 51], ["LIMIT", 1]]
  ↳ app/controllers/api/comments_controller.rb:38
   (0.2ms)  BEGIN
  ↳ app/controllers/api/comments_controller.rb:39
  Comment Destroy (0.8ms)  DELETE FROM "comments" WHERE "comments"."id" = $1  [["id", 51]]
  ↳ app/controllers/api/comments_controller.rb:39
   (2.1ms)  COMMIT
  ↳ app/controllers/api/comments_controller.rb:39
  Rendering api/comments/index.json.jbuilder
  Rendered api/comments/index.json.jbuilder (3.5ms)
Completed 500 Internal Server Error in 21ms (ActiveRecord: 3.7ms)


  
ActionView::Template::Error (undefined method `each' for nil:NilClass):
    1: 
    2: @comments.each do |comment| 
    3:   json.set! comment.id do 
    4:     json.partial! 'comment', comment: comment 
    5:   end
  
app/views/api/comments/index.json.jbuilder:2:in `_app_views_api_comments_index_json_jbuilder__2940510328301300636_70181083474860'
app/controllers/api/comments_controller.rb:40:in `destroy'

presentational component

import React from 'react';

class CommentIndex extends React.Component {

    constructor(props) {
        super(props)
        this.handleDelete = this.handleDelete.bind(this);
    }

    componentDidMount() {
        this.props.fetchComments();
    }

    componentDidUpdate(prev) {
        if (Object.values(prev.comments).length !== Object.values(this.props.comments).length) {
            this.props.fetchComments();
        }
    }

    dateCreated(date) {
        const dateCreated = new Date(date)
        return dateCreated.toLocaleDateString();
    }

    authorInitial(id) {
        const users = Object.values(this.props.state.entities.users);
        const user = users.filter(user => user.id === id);
        return user[0].username.split("")[0]
    }

    authorName(id) {
        const users = Object.values(this.props.state.entities.users);
        const user = users.filter(user => user.id === id);
        return user[0].username
    }

    handleDelete(id) {
        this.props.deleteComment(id)
            // .then(window.location.reload())
    }

    render() {
        const comments = Object.values(this.props.state.entities.comments);
        const videoComments = comments.filter(comment => comment.video_id === this.props.id)

        const commentNumber = function () {
            if (videoComments.length === 1) {
                return "1 Comment"
            } else {
                return `${videoComments.length} Comments`
            }
        }
        const commentList = videoComments.map(comment => {
            return (
                <ul key={comment.id} >
                    <div className="comment-list-item">
                        <div id="left-side">
                            <h2 className="comment-author-initial">{this.authorInitial(comment.author_id)}</h2>
                            <div className="comment-body">
                                <div className="name-date">
                                    <h2 className="comment-author-name">{this.authorName(comment.author_id)}</h2>
                                    <h2 className="comment-upload-date"> commented on {this.dateCreated(comment.created_at)}</h2>
                                </div>
                                <h2 className="comment-text">{comment.body}</h2>
                            </div>
                        </div>
                            {/* {this.props.currentUser.id === comment.author_id ? <button id="delete-button"onClick={() => this.handleDelete(comment.id)}>Edit</button> : null}     */}
                            {this.props.currentUser.id === comment.author_id ? <button id="delete-button"onClick={() => this.handleDelete(comment.id)}>Delete</button> : null}    
                        
                    </div>
                
                </ul>
            )
        })

        return (
            <div id="comment-list">
                <h1 className="comment-page-title">{commentNumber()}</h1>
                <div className="comment-page-container">
                    <ul id="comment-ul">
                        <div id="comment-page-list">{commentList}</div>
                    </ul>
                </div>
            </div>
        )
    }
}

export default CommentIndex;

controller

class Api::CommentsController < ApplicationController

    def index
        @comments = Comment.all
        render :index
    end

    def new
        @comment = Comment.new
        render :new
    end

    def show
        @comment = Comment.find(params[:id])
        render :show
    end

    def create
        @comment = Comment.new(comment_params)
        @comment.author_id = current_user.id 
        if @comment.save
            render :show
        else
            render json: @comment.errors.full_messages , status: 422
        end
    end

    def update
        @comment = Comment.find(params[:id])
        if @comment.update(comment_params)
            render :show
        else
            render json: @comment.errors.full_messages, status: 422
        end
    end

    def destroy
        @comment = Comment.find(params[:id])
        @comment.destroy
        render :index
    end

    def comment_params 
        params.require(:comment).permit(:body, :author_id, :video_id)
    end
end

Answer 1

The cause of the problem is rather self evident:

def destroy
  @comment = Comment.find(params[:id])
  @comment.destroy
  render :index
end

render:index is highly unconventional. An you might be falling victim to a very common misconception - render:index does not call the index method in your controller. It just renders the view.

In a classical Rails app destroying a resource usually will redirect to the index.

def destroy
  @comment = Comment.find(params[:id])
  @comment.destroy
  redirect_to :index, notice: 'Comment deleted.'
end

If you're creating a controller that serves JSON you would typically respond with a just a 204 - No Content response code:

def destroy
  @comment = Comment.find(params[:id])
  @comment.destroy
  head :no_content
end

But you could also respond with 200 - OK if the request body contains an entity like some JSON that describes the status.

By using ActionController::MimeResponds you can do both:

def destroy
  @comment = Comment.find(params[:id])
  @comment.destroy
  respond_to do |f|
    f.html { redirect_to :index }
    f.json { head :no_content }
  end
end