codecore

day22.md

ERD

One to Many

foreign key needs index contraint

bin/rails g model answer body:text question:references

The t.references :question will generate an integer field that

  # is called: question_id (Rails convention)
  # index: true -> will automatically create an index on the `question_id` field
  # foreign_key: true -> will automatically create a foreign key constraint
  #                      for the `question_id` field

class Question < ActiveRecord::Base

This will establish a has_many association with answers. This assumes

that your answer model has a question_id integer field that references

the question. with has_many answers must be plural (Rails convention).

We must pass a dependent option to maintain data integrity. The possible

values you can give it are: :destroy or :nullify

With :destroy: if you delete a question it will delete all associated answers

With :nullify: if you delete a question it will update the question_id NULL

=> for all associated records (they won't get deleted)

has_many :answers, dependent: :destroy

q = Question.last

a = Answer.new(body: "my awesome answer")

a.question = q

a.question_id = q.id

a.save

q.destroy will first delete the answer associated with question then will delete the question

q = Question.last

q.answers.create(body: "Hello")

a = q.answers.new(body: 'HellO')

a.save

Answer.create(body: "hello", question: q)

q.answers

resources :questions do get :search, on: :collection patch :mark_done, on: :member post :approve

resources :answers resources :answers, only[:create, :destroy]

if you define resources as nested rails will define all answers routes prepended with the next routes

Steps

in your controller you must define an instance variable

we can user the form after overiding the url parameter.The downside to i tis that it wont work for "edit" situation. This will work in "create" situation. So we can't reuse it when we decide to implement editing answers.

<%= form_for @answer, url: question_asnwers_path(@question) do |f|%>

<% end %>

This is the prefered approach

<%= form_for [@quetion, @answer] do |f| %>

<%= f.label :body %> <%= f.text_area :body %>

<% end %>

passing an array for "form_for" is a better approach for creating nested resources. This approach will work for both new/ edit situations. so if @answer is not persisted it will send a Post request to question_answers_path(@question). And if @answer is persisted it will send a PATCH request to question_answer_path(@question, @answer)

bin/rails g controller answers

in the answers controller

def create @question = Question.find params[:question_id] answer_params = params.require(:answer).permit(:body) @answer = Answer.new answer_params @answer.question = @question @answer.save render json: params end

adding this will mkae sure that an answer's body is unique for a given question. This means you cant submit the same answer body twice for the same question but you can submit the same answer body for two different questions.

validates :body, presence:true, uniqueness: {scope: :question_id}

def create @question = Question.find params[:question_id] answer_params = params.require(:answer).permit(:body) @answer = Answer.new answer_params @answer.question = @question if @answer.save redirect_to question_path(@question), notice: "asnwer created!" else render "/questions/show"

end

<%= @answer.errors.full_messages.join(", ") %>

<%= @question.answers.each do |ans| %> <%= ans.body %> <%= link_to "DELETE", question_answer_path(@question, ans), method: :delete, data: {confirm: "Are you sure?"} %>

---

<%end%>

def destroy

question= Question.find params[:question_id]

answer = question.find params[:id]

answer = Answer.find params[:id] answer.destroy redirect_to question_path(params[:question_id]) end