Creating a web app from start to finish
Follow a step by step guide to creating a reminders web application using the Petal Pro boilerplate. We will cover everything from setup to deploying to production.
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v2.2.0
Follow a step by step guide to creating a reminders web application using the Petal Pro boilerplate. We will cover everything from setup to deploying to production.
Last updated
Was this helpful?
For this tutorial you will need:
For deployment (optional) you will need:
Once it's unzipped we can go ahead and rename the folder to whatever we want to call it. In our case, we're going to call it "remindly".
Let's get the server running so we can see Petal Pro in action. Simply run in your terminal:
And now navigate to http://localhost:4000 in your browser to see the dummy landing page:
Feel free to have a look around the website.
The mix setup command helpfully ran our seeds.ex file, which if you open you will see this code:
The UserSeeder.admin() function has created an admin for us. You can sign in as this admin with the details below:
Obviously, the Petal branding will need to be replaced by your own brand. If you do a global search for "SETUP_TODO" you will find the code you need to modify.
The first mention you can ignore. The second match is in our config.exs file. Here we can update our web apps details:
The next SETUP_TODO is found in the file dev.ex, which is to regenerate and replace the provided secret_key_base with mix phx.gen.secret
The next SETUP_TODO is found in the file core_components.ex.
When you're ready to export you can highlight them all and click "Export":
Once you've exported them all you can drag them into your project:
I recommend uploading your logo in png format to some kind of image hosting you like (at least until you have a production server hosting the images for you). We personally like Cloudinary so let's upload our logo and then paste the URL into our config file. After you've done this, you can just paste the link in and your emails should reflect your new logo. We'll also discuss this later in the "Reminder emails" section of this tutorial.
Now restart your server, reload your browser and check out your new logo!
The other SETUP_TODO's are self-explanatory - they involve adding your license and privacy policy content as most SAAS applications will require them. You can add this content in pure markdown and we've provided some dummy content as an example to get you started. It's not really needed until you go live to production so you can put it off for now.
Petal Components relies heavily on mapping colors to different types, such as "primary", "secondary", "success", etc. This mapping is done in the tailwind.config.js file.
By default, primary is blue and secondary is pink:
In our case, we'll go for the colors "amber" and "slate":
If you refresh your landing page, you'll notice the color change.
The landing page consists of content from two core files:
lib/remindly_web/components/landing_page_components.ex - a set of components like <.hero>, <.features>, <.header> etc. The end goal of Petal Pro is to have a comprehensive set of landing page components that can be used as building blocks for your landing page. Ideally, you won't modify these too much but will use them just like Petal Components. For now, you can modify them as you wish.
/lib/remindly_web/controllers/page_html/landing_page.html.heex - a template file that uses the components from landing_page.ex
To keep this tutorial moving quickly, we won't do much design work on the landing page - if you open up landing_page.html.heex we can strip it down to merely a hero component:
Now refresh your landing page and it should be a lot more simple. It is up to you how detailed you want to be with your landing page.
Now that the public-facing side of things is looking good enough, we can work on the app itself.
When a user signs in we want them to see a list of their reminders that they can check off or delete, with a button to create new ones. Normally, this would be a job for a Phoenix generator - luckily Petal Pro has its own version of the mix phx.gen.live generator - mix petal.gen.live. Our generator produces the same files as the Phoenix one, but the resulting HTML will use Tailwind and Petal Components so we don't have to worry about styling.
Let's run the generator to create the following schema:
label
:string
due_date
:date
is_done
:boolean
user_id
:integer (foreign key)
Note that the command ends with the --data-table switch. This will generate the index page using the Data Table component. If you'd like to use the Table component instead, omit the switch. Without going into too much detail, the Data Table has more features (e.g. sorting) but the Table component easier to understand.
The command will output the routes needed to make the new pages work. Highlight them and just copy them to your clipboard for now.
Let's run the migration the generator just created:
Now we need to add these routes to the router. We can search for the text "Add live authenticated routes here".
Let's paste the routes we copied from the generator command below that line.
Petal Pro defaults to scoping authenticated routes within the “/app” namespace. To continue this naming convention we need to edit the routes within the generated code. To do this you can do a "find and replace all" within the reminder_live folder.
Replace ~p"/reminders with ~p"/app/reminders.
Since it's in a protected area, we'll have to sign in before reaching this new page. Click the sign-in button in the top right dropdown:
We have an admin user seeded, but let's sign up as a new user. Click "Continue with passwordless":
Type in any email for now.
Now check your logs for a pin code:
After submitting the pin code you have a new user! No need for passwords.
Upon your first sign in you will be greeted with an onboarding screen.
Showing this screen is determined by the user field user.is_onboarded.
All new users have this defaulted to false, and thus will see this screen thanks to the OnboardingPlug that redirects to this page if current_user.is_onboarded == false.
Over time you might add more onboarding fields like "Where did you hear about us?" or "How many people are in your company?".
Onboarding can be switched off by removing the OnboardingPlug from all pipelines in the router. There is further explanation for this in onboarding_plug.ex
Just hit submit to get through the onboarding and you will then be shown a dashboard that we will ignore.
Instead, manually navigate to "http://localhost:4000/app/reminders" to see the newly created CRUD functionality.
You'll notice there is no layout. This is because we have to add that ourselves. We'll do that in a little bit. Firstly, let's get it running properly.
One issue with the generator is that it doesn't handle foreign keys very well. Currently, the reminders page shows reminders from ALL users. In fact, the reminder.user_id is not even being set when creating a new reminder, so they're not owned by anyone - every user who signs in will see them. We need to make it so everything is scoped to the currently signed-in user:
the index page table should only show the current users' reminders
when you create a new reminder, it should set the user_id to the current user's id
the show page should not be allowed to see other user's reminders
Firstly, there are a couple of problems with the schema file:
Let's fix those up:
The reminder schema now knows it belongs to a user, but we still have to let the user schema know that it "has_many" reminders. Let's add that to the user schema file:
Now go to index.ex in your reminder_live folder and let's modify the `assign_reminders` function:
Notice how the starting_query has changed? It now doesn't just fetch all reminders, but only the ones that belong to the signed-in user.
Great, the association is now complete. Now let's make it so that when you create a new reminder, the reminder.user_id gets populated with the signed-in user's id.
The code for creating the reminder is located in lib/remindly_web/live/reminder_live/form_component.ex :
Let's modify this to ensure the :user_id is set in the params:
Now when you try and create a new reminder, unfortunately, you get an error:
The current_user isn't in socket.assigns. This can be confusing because it is usually in the socket's assigns thanks to Petal Pro setting it in user_on_mount_hooks.ex.
The reason it isn't in this case is that form_component.ex is a live_component, not a live_view. Thus it has its own state and it's up to us to pass any assigns into it. We can see in index.html.heex the assigns being passed into it:
So all we need to do is pass in the current_user to this live_component function:
And now creating a new reminder works correctly 🎊.
The next problem is that in some browsers the date picker starts too far in the past - ideally, it'll show today's date. So let's add a default date for the form. This also will be done in the RemindlyWeb.ReminderLive.Index live view (index.ex). We can modify the existing function, so it looks like this:
We use the Timex library (included in Petal Pro) to get today's date. Now the default is set correctly when creating new reminders (although since we're using UTC time, it may be 1 day off depending on where you live, but good enough for this tutorial).
The "Is done" column with true or false is a bit ugly.
Let's move it to the front column and make it a checkbox. Working in the file index.html.heex, let's begin by rearranging the headers:
Next, we'll add an icon in the first cell that shows whether the task is done or not.
Here we use :let={reminder} to expose the reminder variable to the inside of the :col slot. If the user clicks the icon, it calls the toggle_reminder event.
Let's create the event handler for "toggle_reminder". Add this event handler to the index.ex file:
Now our checkbox is in sync. Live view works so fast that you can barely notice it's not a Single Page App. However, this won't always be the case once if someone is a long way from the server and has some latency.
With LiveView you can simulate latency. If you look in app.js you'll find a comment with a command to run the in the browser console. This will add 1 second of latency: liveSocket.enableLatencySim(1000). Run this in your browser console to see the lag.
LiveView adds classes when it's performing some kind of communication with the server. Phoenix helpfully adds a plugin to your tailwind.config.js file that allows you to target these classes:
Let's make use of this and add a spinner while waiting to hear back from the server.
With that working correctly, we can disable the latency in the browser console: liveSocket.disableLatencySim().
Now that our table is working nicely, let's add the layout back in.
And do the same with show.html.heex. The problem now is the sidebar menu doesn't show a link to the reminders page. Let's change that.
Each menu item has a function that looks like this:
From these function definitions, we can construct menus. There are two core menus - the main menu, which appears on this side panel, and also the user menu, which is in this dropdown.
Since we want to modify the sidebar, we want to change the main menu for a signed-in user. Let's replace :dashboard, :orgs and :subscribe with :reminders
Lets also rename :dashboard with :reminders in the user menu:
However, this won't work yet as we still need to write a definition function for :reminders. Scroll down the file until you see the get_link/2 function for :dashboard. Let's overwrite this function and replace it with our reminders menu item:
Next, we want this new route to be our kind of "home" route for signed-in users (eg. redirect here after being signed in, or when you click the logo in a layout). To set this, go to helpers.ex and look for the home_path/2 function:
Here we can simply add the path of the new menu item:
Now refresh the page and we can see the sidebar has been updated!
We've found that at some point in building a web application, you need to implement some kind of logging functionality. You or your client will want to see some stats on how your users are using your web application.
Petal Pro puts logging at the forefront and encourages you to log as much as you can. By default, it will store logs in your Postgres database, but there's no reason why you can't shoot them off to a 3rd party provider.
To showcase Petal Pro logging, we'll create a log every time a user creates a reminder and toggles it to "done". If you look in the file log.ex, you will see we have a list of actions that can be logged. Let's add our new log actions:
Now we can do the actual logging. Go to form_component.ex and add a log in the create action.
You will see we're adding some metadata. It is up to you whether or not for new tables like "reminders" you create a migration and add a foreign key to the logs table (log.reminder_id). To keep it simple we can make use of a JSONB column on the logs table called metadata (JSONB is better than a JSON column as it allows for faster searching and even indexing). In this column, we can store any kind of map we want. We'll store the ID and label of the reminder here so we can track it if need be.
Now create a new reminder and we'll check that our logs have been updated. Logs are in the admin section. But to be able to see them you need to be admin.
When we seeded the project we added an admin user. You can sign out then sign back in with these credentials:
Email: admin@example.com
Password: password
Once signed in as admin try clicking the user menu (your avatar up the top right), and select "Admin".
Then click logs on the sidebar menu. Here you should see a new log for creating a reminder.
Let's do another log for when we complete a reminder. We'll need to modify our toggle_reminder function in index.ex.
Now, when we toggle a reminder to "done", a new log will appear.
You might have noticed a toggle for "Live logs" on the logs screen. If you turn this on, you will actually get a live feed of what's happening in your web app. You can try it out by opening two browser windows side by side: one on logs with "Live logs" checked, and one on the reminders screen. If you toggle the reminder on and off, you will see the logs appearing on the admin screen in real-time:
Note that if it isn't working you might have to restart your server.
Next, we need to implement an email reminder that gets sent the day a reminder is overdue. If we head to "Dev", and then click on "Email templates" we can see a list of our transactional emails.
We want to create a new one and show it here so we can visualise it while we develop it. Before we do, let's do a quick overview of how emails work in Petal Pro. Open up notifications/email.ex and you will see a list of functions that generate Swoosh email structs. Eg:
If I run this function in IEX I can see the Swoosh struct:
A Swoosh.Email struct can be delivered to an email address by a Swoosh mailer (see mailer.ex). Eg:
So email.ex creates the Swoosh structs and the functions for actually delivering emails like the previous code example are in user_notifier.ex. Think of email.ex functions like view templates, and user_notifer.ex functions like controller actions.
So our steps will be:
Create the function to generate a Swoosh struct in email.ex
Ensure it looks good by creating a new action in email_testing_controller.ex that simply renders the html_body value of the struct
Create a new user_notifier.ex function for use in our application
Create a CRON job that runs once a day that finds overdue reminders and emails the user using the user_notifier.ex function
In email.ex, let's create a function for our new email:
Now it expects a template reminder.html.heex. Let's add one to the /lib/remindly_web/templates/email folder:
Emails are notoriously hard to code and work across the myriad of email providers, so we created a template and included some components to help with the basics like a centered button or gap. See email_components.ex for these.
Now we can try seeing how it looks. Open up email_testing_controller.ex and do two things:
Append "reminder" to the end of @email_templates
Create a new generate_email/2 function for our new email
Now if you refresh the "Email templates" page you can see your new email design:
I recommend uploading your logo in png format to some kind of image hosting you like. We personally like Cloudinary so let's chuck our logo up there and then paste the URL into our config file.
Great, now that the email is ready to go we can implement the user_mailer.ex function that accepts a reminder Ecto struct as a parameter and sends the reminder email for us:
Now we can test a sent email in IEX:
Click on "Sent emails" in the sidebar to see that it worked properly. If we cmd-click the button it should take us to the right reminder.
We create a worker Remindly.Workers.ReminderWorker, which has a function perform/1 that will find overdue reminders and send the reminder emails
We tell Oban to run this worker once per day
Petal Pro comes with an example worker you can check out (example_worker.ex). In the same folder, let's create reminder_worker.ex:
And then enter this code snippet:
Now we have a skeleton worker we can work with. Try testing it out in IEX:
Now we need to find all the overdue reminders. This is a job for the context file reminders.ex. In there we can add the following function:
Normally we'd write a test for this, but for brevity, we'll assume it works correctly (or you can test it in IEX if you like).
Back to the worker, let's finish it off:
We can test it by setting one of our reminders in the past (making sure it's unchecked) and then running the worker in IEX again.
You can double-check by also looking at the "Sent emails" page again.
Now that we know our worker works, we want to schedule it to run every day. This is a simple task thanks to Oban - just modify config.exs:
And that's it! Our job will now run daily.
To deploy your new app to Fly.io, use the following guide:
You've just gone from nothing to production. Obviously, this app needs some touching up, but it gives you an idea of how to do things. We look forward to seeing what people create with Petal Pro.
Access to Petal Pro (you can purchase it on )
Elixir & Erlang installed (you can follow our to get up and running)
PostgreSQL running: works well for Mac or we have a docker-compose.yaml file that will run Postgres for you
An account on
An with (SES) for emails (you can replace with another service if you like - it just won't be covered in this guide)
Head over to the and create a new project, then download v2.2.0. You can unzip it in your terminal with the command unzip petal_pro_2.2.0.zip.
While this changes the folder name, we still need to change the name of all the files and module names (eg. petal_pro_web.ex should be remindly_web.ex, etc). We have created a library to do this called .
You don't need to change anything in this file, but rather it's asking you to update the logos with your own. For this tutorial, I went into Figma and just wrote "Remindly" in an interesting font. You can duplicate and replace it with your logo if you like.
You can pick any two colors from . Or if you want to go custom, you can try out .
Note that we are using the . You can dig into how this component works by opening it in your editor with:
In Petal Pro we try to keep our menu items all following the same data structure (name, label, path, and icon, which refers to a ). Menu items can be constructed on the fly, but if it's commonly used we can store them in menus.ex. This file is like a small database for menu items. It also can omit menu items if a user doesn't have the right privileges (eg. admin menu items).
The icon is passed directly to the .
You can browse and when you've found the one you like, just prefix it with "hero". For example, the icon "bookmark-alt" would be "hero-bookmark-alt"
With an email ready to be sent to people who have been lazy, let's create a CRON job to send off the emails. We use for jobs, which supports a CRON schedule (CRON just means a time schedule). Here's what we'll do:
To keep it simple we'll use the @daily code for scheduling. If you want to fine tune it to the exact minute, you can use the usual CRON syntax (you might need to help you generate it).
Congratulations!
If you have any feedback, head to see how to get in touch.
