How to Upload Photo and Get Url
How To Upload Images to a Track API — And Get Them Back Once again
With a Rails API, paradigm uploading isn't as simple as information technology seems
I'd given myself a week to write a Rails API back end for Supagram, a lightweight, browser-based Instagram clone featuring posts, likes, and a chronological activity feed from the users you follow.
The biggest difficulty I foresaw was the polymorphic database relationships between users in their various roles equally follower, followed, liker, and so on. Little did I know that the least intuitive affair to get working would actually be the unproblematic concept around which all of Instagram is congenital: image uploading.
Let me walk you through the problem. This server was required to:
- Have an epitome file from the React front end end
- Associate the epitome with a newly created mail service record in the database
- Upload the paradigm to a content delivery network like Cloudinary or AWS for storage and retrieval
- Fetch the image URL and render it as confirmation of the mail service'south creation and in subsequent GET requests to the activity feed
The existing resource on how to do this are extremely fragmented. Much had to be inferred or jury-rigged for the specific context of a Rails API. Here's the definitive, footstep-by-step guide to save yous the hurting.
1. Accept an Epitome From a JavaScript Front
There are two mutual ways to ship prototype uploads to a server: as FormData, or as a base64 cord. There are considerable performance disadvantages to base64 encoding and transmission, then I chose FormData.
I'll be using React components to demonstrate, but FormData is a web API — information technology'southward not constrained to whatsoever particular framework, or fifty-fifty JavaScript itself.
Here a simple HTML course takes a caption and an image to upload. The names of the fields should lucifer the parameters your API endpoint is expecting to receive, in this case explanation and image.
On submit, we foreclose the default form behaviour (which refreshes the page) and use JavaScript's FormData constructor to create a FormData object from event.target — the whole grade.
That done, we make our first call to the API:
In that location are two of import things to note about the config object for this asking:
- There is no
"Content-Type"cardinal in the headers — the content type ismultipart/grade-data, which is unsaid by the FormData object itself. - The body is not stringified. The FormData API handles all the necessary processing for the image to exist sent over the web.
The say-so header is optional and will depend on the requirements of the endpoint you're posting to. In the case, the endpoint I'thousand using is represented by POSTS_URL.
2. Associate the Image With a Newly-Created Mail service Tape in the Database
On the back end, I used ActiveStorage to create associations between images and their owning objects. It's the standard gem for file associations as of Rails v.ii and is steadily replacing older solutions similar CarrierWave and Paperclip.
To get started, simply run rails active_storage:install. It will create migrations for ii new tables in your database, active_storage_blobs and active_storage_attachments. These are managed automatically; yous don't need to bear on them. Run rails db:migrate to complete the process.
Past default, ActiveStorage will employ local storage for uploaded files while running in a evolution environment. In product, this is near certainly not what you want. It likewise poses some unique challenges for returning prototype URLs from the server. We'll configure this properly in part iii, afterward we take a look at our Post model and accompanying endpoint.
Postal service migration/model
Study this migration for my post model. There's something odd most it.
Y'all'll detect that in that location is cypher about an prototype hither. Neither the epitome nor a reference to the paradigm lives in the Posts table.
Now check out the model:
The essential line here is has_one_attached :image. This tells ActiveStorage to acquaintance a file with a given case of Postal service.
The name for the attached object should match the parameter beingness sent from the front end end. I've chosen it :prototype, because that'southward what I named the corresponding upload form field. You can call it whatsoever you like, so long as the forepart stop and back end agree.
As a bonus, I've added validation to ensure that posts cannot be created without images. Modify this to suit your purposes.
Curious about the include argument and my get_image_url method? Permit'due south inspect the post creation endpoint before coming dorsum to these.
Postal service creation endpoint
The post_params method is arguably the most important hither. The data from our front end has ended up in a Rails params hash with a body that looks roughly like: { "explanation" => "Slap-up caption", "image" => <FormData> }.
The keys of this hash must match the attributes expected by the model.
My item post model requires a user_id, which wasn't sent in the request body only is instead decoded from an Authorization token in the request headers. That's happening behind the scenes in get_current_user(), and you don't need to worry near it.
When you lot pass post_params() to Post.create(), ActiveStorage kicks in, saves a file based on the FormData contained inside the paradigm param, and associates the file with the new Postal service record. If yous're using local storage, images will be saved in root/storage by default. However, that'south probably non what you want.
3. Upload the Image to a CDN for Storage and Retrieval
Local storage eats up infinite and can't compete with the delivery speeds of dedicated content commitment networks like Cloudinary and AWS. Whatsoever your purposes, it's a good thought to familiarise yourself with these essential services.
Cloudinary is exceptionally user-friendly and like shooting fish in a barrel to integrate with ActiveStorage, and so that's the approach I took for this projection. From this betoken on, I'll assume that you lot already have a (free) Cloudinary account. If you lot'd prefer to use another service, don't worry — the approach is largely the same for all major providers.
Beginning, add together the cloudinary gem to your Gemfile and run bundle install.
Then, in /config, open up ActiveRecord's storage.yml configuration file and add the following. Don't modify anything else.
Side by side, navigate to config/environments/evolution.rb and ./production.rb, and set up config.active_storage.service to :cloudinary in each. Your test surround will keep to use local storage past default.
Finally, download the cloudinary.yml config file from your Cloudinary dashboard and place information technology in the /config folder.
Circumspection: This file contains the secret fundamental for your Cloudinary business relationship. Do not share this file or push it to your git repo, or your account tin be compromised. Include /config/cloudinary.yml in your .gitignore file. If you do reveal these details by accident (I'chiliad speaking from feel), immediately conciliate the compromised key and generate a new i via your Cloudinary dashboard. Update cloudinary.yml to reflect the new secret fundamental.
With this in place, ActiveStorage will automatically upload and retrieve images from the cloud.
4. Fetch the Image URL and Return It
This is the least intuitive part of working with ActiveStorage. Getting images in is piece of cake plenty. Getting them out again without guidance is like solving a 12-sided Rubik'southward cube drunk.
It becomes especially convoluted if, like me, you want to move the logic of building your endpoint's response into a defended serializer form.
In my posts controller respond_to_post() method, I first cheque if the new post is valid and, if so, create an case PostSerializer from the new post and the current user, and render JSON with the serializer's serialize_new_post() method.
In PostSerializer, I pull together details about the post, including the URL that will redirect our end user to the prototype hosted past Cloudinary. If it seems odd to explicitly pass the instance variable @postal service to the instance method serialize_post, ignore information technology — information technology'due south a requirement of other PostSerializer functions that aren't relevant to this mail. If you're curious, the full source code is here. Similarly, the contents of the serialize_user_details method are unimportant.
Simply how, exactly, does post.get_image_url() work, and where does it come from?
This is a method I defined on the Post model itself, the paradigm URL being a pseudo-aspect of the post. It fabricated sense to me that the post should know nigh its image URL.
To access the URL that ActiveStorage creates for each image, we utilise Rails' url_for() method. But in that location'due south a snag: Models don't normally have access to Runway' url_helpers. It'southward necessary to include Rails.application.routes.url_helpers at the height of the class before yous can utilize it.
If you try to striking your endpoint from the front end at this stage, you'll likely see this fault on the back end:
ArgumentError (Missing host to link to! Please provide the :host parameter, set default_url_options[:host], or prepare :only_path to true) To resolve it, navigate to config/environments/development.rb and add Rails.application.routes.default_url_options = { host: "http://localhost:3000" } (or your preferred development port, if not 3000). In ./production.rb, do the aforementioned, using the web root of your production server as the host value.
If information technology's all working correctly, your endpoint will now render beautifully formatted JSON that includes an epitome link. When clicked or loaded, it will redirect to your Cloudinary-hosted image.
Commit your work, push it to Github, and exhale a sigh of relief.
Source: https://betterprogramming.pub/how-to-upload-images-to-a-rails-api-and-get-them-back-again-b7b3e1106a13
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