If I'm using my rails app to mainly respond to json, is having a "new" or "edit" action that returns an empty object in json still necessary/useful? For example:
def new
#post = Post.new
respond_to do |format|
format.json { render :json => #post }
end
end
I feel like I can just get away from making a server call by completely building the forms in html
In my opinion, yes, you can exclude that action if you don't need special default field values and are assembling your form fields manually.
Related
I have a new and create method:
def new
#post = Post.new
puts #post
puts #post.object_id
end
def create
#post = Post.new(post_params)
puts #post
puts #post.object_id
respond_to do |format|
if #post.save
format.html { redirect_to #post, notice: 'Post was successfully created.' }
format.json { render :show, status: :created, location: #post }
else
format.html { render :new }
format.json { render json: #post.errors, status: :unprocessable_entity }
end
end
end
For a while I thought that the create method had some rails magic tied to it where it knew how to get the instance of a model from the new method and then create it in the DB.
Realizing that this is incorrect, then, is the reason we call Post.new in the new method so that we have access to the form helpers for the object and its attributes and can pass those into Create as parameters?
Then in create... We call Post.new(params)... To me in the code it doesn't look like we explicitly call .create or .save anywhere (yes I see we check for a condition that yields true or false using save). So how does creating a new instance of an object and passing it parameters save it?
I am a little lost and am looking for some clarification, confirmation, general assistance on these beginner questions.
Or maybe I should stick with golf.
is the reason we call Post.new in the new method so that we have access to the form helpers
Yes, essentially. It allows you to use, for example, form_for #post.
To me in the code it doesn't look like we explicitly call .create or .save anywhere (yes I see we check for a condition that yields true or false using save)
Using if #post.save is calling #post.save. That saves the post, and returns true on success and false on failure. Methods can do things and also return values, and this method persist the record and returns a boolean.
When you run this line
#post = Post.new(post_params)
You are creating a new instance of Post with the parameters that are allowed, post_params is a method that is defined in the controller that permits certain attributes.
def post_params
params.require(:post).permit(:title, :content)
end
In this case, only title and content are permitted to be created with the post. The post will most likely also have a created_at, and updated_at attributes, but that is automatically set, so it is not an attribute that the user can edit/create. You can read more about strong parameters
The if statement reads
if #post.save
This is basically saying if the post can be saved without error, save the post and run the code in the if statement.
Think of it as saying if the post was successfully saved, then do this.
There are few thing to consider...
we are in RESTful environment.
Why we use Model.new
its mainly to get(GET REQUEST) the empty model to provide for the user to fill in the information.So here comes the form helpers which is used to fill in the details in the form and fill the empty bucket for the model which is the attributes and the values provided by the users using the form.
So basically ,you are only providing an emtpy record...that can be used for the user to fill in.
Why do we again user Model.new(params)
So,in continuity with above explanation,once the bucket is ready from the user,we use the create action in the form to post the data (POST REQUEST)
.So that data,if you see your sever logs in wrapped in an parent node...like
Processing by PicturesController#create as HTML
Parameters: {"picture"=>{"title"=>["testing"]}
picture model
this data is wrapped in params which you define at the controller level since Rails 4,which is as easy a using it directly like Model.new(params) which is nothing but Model.new(title: "testing") which is use to create a new object-needed for validation/callbacks to check whether user has provided valid details.
Hence,you check this with if/else statement which most rails create action has.
..HOPE IT HELPS
Rails scaffold generated the following:
respond_to do |format|
if #student.save
format.html { redirect_to #student, notice => 'Student was successfully created.' }
format.json { render :show, status: :created, location: #student }
else
format.html { render :new }
format.json { render json: #student.errors, status: :unprocessable_entity }
end
end
After reading this I understand how the respond_to is working (sort of), but I don't get what format is doing. Shouldn't it be either format.html or format.json and not both? What are these two lines actually doing?
format.html { render :new }
format.json { render json: #student.errors, status: :unprocessable_entity }
Is there an implied if in there? Is it something like
if (format == html) {}
if (format == json) {}
Side note: Why does update require the respond_to block while show will handle /students/1.json or /students/1 without any logic at all?
format is a local variable that respond_to yields. When you do format.html {} you are actually registering a callback block for a format.
Rails goes through the registered formats and tries to find a compatible format to the MIME type in the request. If there is no handler it will raise an error.
This could be explained as something like using syntactic sugar on top of a case statement (the Ruby equivalent of a switch statement). But the analogy is not completely accurate since Rails does a bit of work in matching the request type.
Also the code inside your block is not executed when the format.html block is registered (as it would be if it was just a conditional statement) but rather when respond_to finishes or not at all if you are using for example E-Tag caching.
Why does update require the respond_to block while show will handle
/students/1.json or /students/1 without any logic at all?
Rails handles many actions by using a convention over configuration approach and guessing the intent of the action.
def PostsController < ApplicationController
def index
# rails auto-magically fills in the controller with something
# like this
#posts = Post.all
respond_to do |format|
format.html { render :index }
format.json { render json: #posts }
end
end
def show
# convention over configuration is awesome!
#post = Post.find(params[:id])
respond_to do |format|
format.html { render :show }
format.json { render json: #post }
end
end
def new
#post = Post.new
render :new
end
def edit
#post = Post.find(params[:id])
render :edit
end
end
Rails assumes that there is a resource with the same name as the controller and auto-magically fills in the controller action. It also assumes there is a view in app/views/posts/(:action).html.[erb|haml|slim|jbuilder]. This is known as implicit rendering.
The comments show roughly what action rails attempts.
It does not fill in actions which operate on data (create, update, destroy) since the actual implementation can vary greatly and it's hard to make useful guesses.
Well, it depends on the format of the request. If a request demands HTML from the server, format.html block will be executed, and in the same way, if a request demands JSON format, format.json will be executed.
Rails will automatically(read: magically) handle the if (format == html) part for you. All you have to do is fill in the blanks. Same way, you can write a block for XML starting with format.xml.
And for the side note, I think you have said it otherwise. update method doesn't require respond_to block, while show requires. And the reason is very simple: update method is there to update the Model, and then, redirect you to somewhere, while show will always return you something. In your case, /students/1 will return you the first student created in the database, and the response will be HTML, while /students/1.json will return you the same result, but response will be JSON this time.
Well you could very well replace 'format' with 'foo' or 'banana' or whatever you want. It is just the variable name in this case because the variable that is sent to your block by respond_to is passing along the format as requested by the incoming http request's Accept header.
Sometimes you'll see 422 "Unacceptable" errors in your logs because you are receiving a request with an Accept header that does not request a mime type your app knows about.
As it is, your callers should be using a browser or be a JSON consumer sending the proper headers to receive responses from the boilerplate.
I need a string of html (something like "<html><body>Hello World</body></html>") for faxing purpose.
I wrote it into a seprate erb file: views/orders/_fax.html.erb ,
and try to render the erb in action: html_data = render(:partial => 'fax').
Here is part of the controller that raises the issue:
respond_to do |format|
if #order.save
html_data = render(:partial => 'fax')
response = fax_machine.send_fax(html_data)
......
format.html { redirect_to #order, notice: 'Order was successfully created.' }
format.json { render json: #order, status: :created, location: #order }
else
format.html { render action: "new" }
format.json { render json: #order.errors, status: :unprocessable_entity }
end
end
It gave me an AbstractController::DoubleRenderError as below:
AbstractController::DoubleRenderError in OrdersController#create
Render and/or redirect were called multiple times in this action. Please note that you may only call render OR redirect, and at most once per action. Also note that neither redirect nor render terminate execution of the action, so if you want to exit an action after redirecting, you need to do something like "redirect_to(...) and return".
How to solve this problem?
If you only need the rendered HTML, and don't need any functionality from the controller, you might try using ERB directly within a helper class, eg.:
module FaxHelper
def to_fax
html = File.open(path_to_template).read
template = ERB.new(html)
template.result
end
end
The ERB docs explain this in more detail.
EDIT
To get the instance variables from the controller, pass the binding into the result call, eg:
# controller
to_fax(binding)
# helper class
def to_fax(controller_binding)
html = File.open(path_to_template).read
template = ERB.new(html)
template.result(controller_binding)
end
Note: I've never done this, but it seems workable :)
Use the #render_to_string method
it works the same way as the typical render method but useful when you need to add some templated HTML to a json response
http://apidock.com/rails/ActionController/Base/render_to_string
If you don't want to escape html, just call .html_safe on it:
"<html><body>Hello World</body></html>".html_safe
Re your error, please post your OrdersController - looks like you are calling render or redirect more than once in the create action.
(Btw, just in case you are trying it - you can't render a partial in a controller - you can only render partials in views)
Edit: yeah your problem is you trying to render a partial in the controller action. You could use an after_create callback to set up and send the fax - though again you won't want to use a partial (as they are for views). http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html
Edit: for your fax problem,you could create a normal Ruby Class, see this excellent bit of advice from Yehuda: https://stackoverflow.com/a/1071510/468009
The reason is you cannot render or redirect inside the same action more than once at a given time.
But in your code, you have both render and redirect. I think in your controller you can use simply only the render, assuming you don't need any json output.
Try this
def create
#order.save
render(:partial => 'fax')
end
I haven't tested this, but I guess you get the idea :), and think about a way to handle errors as well (in case order didn't save).
Suppose you have an edit form with :remote => true. Your controller method looks like
def update
#article = Article.find(params[:id])
respond_to do |format|
if #article.update_attributes(params[:article])
format.html { redirect_to #article}
format.js { render :js => "window.location.replace('#{article_path(#article)}');"}
else
format.html { render :action => "edit" }
# Render update.js.erb which replaces the body of the form
format.js {}
end
end
end
What's the best way to do the redirect on successful article update in Rails 3.2.1? The raw JS solution seems a little sleazy, but I do like the fact that it's obvious that it's performing the same function as the format.html version.
I would prefer a solution that does not use RJS (if that even works in Rails 3.2?)
How about adding the below line of code on the view file itself
#some_file.js.erb
`window.location = redirect_path
As you mentioned in the question you do not prefer RJS, but I think it's better to follow this pattern better than writing the js code in the controller.
Does your ajax interact with a model (.php,.asp?). My preferred method in this instance is to create a success/fail criteria within the model after submission and redirect directly from there. Not sure if that makes sense in this application though?
I'm a newcomer to Rails, and have been following the tutorial on the rails webpage.
Using the scaffold instruction to create a "post" model, I found that the new action in the controller has a special directive for XML format:
def new
#post = Post.new
respond_to do |format|
format.html # new.html.erb
format.xml { render :xml => #post }
end
end
I can't see the reasoning for supporting an XML request when creating a new post. Browsing to /posts/new.xml returns nothing. What is the purpose of this?
The reasoning for it behind the new action is simply to provide a xml client with the default data (or something else if you want).
The format directive is being used by all routes, and you don't need to support a format unless you want to.
The above code could might as well have looked like:
respond_to do |format|
format.html # renders new.html.erb
format.xml { render :xml => {:message => "XML is not supported"} }
format.json { render :text => #post.to_json }
format.js # renders new.js.erb
end
Also, this is not limited to the new action, but is available in all your actions. The format to use is either taken from the url (if the route is set up to use it), or from the HTTP-Accept header that the browser sends.