A look in to the future 🔮 A lot of time you need to make a system that can send out to yourself or other users , specifically events related to changes in your database. and make this ridiculously easy. notifications based on events Postgres Phoenix By the end of this post you will have: short Setup a Phoenix 1.3 project Setup a broadcast function and trigger in Postgres Used a GenServer to listen for broadcasts from Postgres Used Bamboo to send emails to yourself when users signs up or changes their payment plan. Getting Setup Before you start Please make sure you have the following installed and/or ready to go: Elixir Phoenix PostgreSQL A valid account SendGrid Initialize the project Lets create a new Phoenix 1.3 project called pub_sub_demo mix phx.new pub_sub_demo cd pub_sub_demo mix ecto.create Add Two Additional Dependencies Next we want to add to help with decoding strings sent from the database and to help us send emails. HTTPoison Bamboo To do this in your file add the following to your : mix.exs deps {:httpoison, "~> 1.0"},{:bamboo, "~> 0.8"} Also update the section to include extra_applications :bamboo extra_applications: [:logger, :runtime_tools, :bamboo] Create a model Finally lets create the model we will be using to show off all of this broadcasting goodness. User mix phx.gen.context Accounts User users name:string payment_plan:string Note: We created the _User_ in a new context called _Accounts_ . If you are unfamiliar with contexts they are nothing to be afraid of just a convention phoenix uses to group functionality. They are not special, just a way to bag functions together. Kick it off! Migrate the database, grab your dependencies and lets go! mix ecto.migrate Note: You should now be able to navigate to _localhost:4000_ and see your application running. Though for the purposes of this demo you wont really be viewing any screens. Broadcast Changes with Postgres The whole idea of this is for Postgres to let know when things have changed. To do so we need to set up two things: US A function that takes an action ( , , ) performed on a row for the purpose of broadcasting it outside of the database. INSERT UPDATE DELETE A trigger that calls this function when an action has occurred on a specific table. Create the Ecto Migration mix ecto.gen.migration broadcast_users_table_changes Add the Function and Trigger Update the migration file you created above to include the following If you want to better understand what is occurring here check out this blog post by @kaisersly which largely is the inspiration for what you are reading here: https://medium.com/@kaisersly/postgrex-notifications-759574f5796e Listen for Changes Now that we have our database broadcasting changes that occur on our table we need to be able to listen and act on the same channel. Thankfully Postgrex provides this by default using . users Postgrex.Notifications To use this we must create a responsible for listening to and acting on the messages broadcast. GenServer Postgrex Creating our GenServer Create the file and populate it with the following: lib/pub_sub_demo/pub_sub/listener.ex For now all that this does is listen on a channel provided and log the messages broadcast to that channel. Next lets configure this as a Worker and give it the channel it will listen to. Hook up the listener Update the file so that it starts the we just defined with the appropriate channel. application.ex Listener users_changes See it in Action You should now be able to start your application again by running: mix ecto.migratemix phx.server Then any change you make to the table via Postgres’s CLI should be output to our Applications . users stdout Listening for Specific Actions While it’s nice to be able to see that occurs in the database often we only care about a small subset of these changes. Specifically for this demo: everything User created User subscription updated Luckily Elixir’s pattern matching provides a wonderfully simple way to cut down on all the noise and focus exactly on the shape of data you’re looking for. What we want to do is update to send the payload to a function that will match on the events that matter. handle_info The above only acts on only the exact events we are looking for and outputs a specific message to our log. Anything else is ignored. Link it up to an email service Standard out is nice but in a running application you don’t want to be combing logs for events that your business cares about, you want to be notified in realtime. Lets hook our messages up to an email provider so that we get a notification right in our inbox when a user signs up or upgrades their plan. The Elixir library and service make this far too easy. Bamboo Send Grid Setup Bamboo Add the following to your file config.exs Note: Bamboo offers many more adapters than just Send Grid if you have a different preference. https://github.com/thoughtbot/bamboo#adapters Create a file in your folder mailer.ex pub_sub_demo Sending emails from our Listener Update in to send our log messages to our own email address. handle_user_changes listener.ex Run it for a Final Time Now if you create or update a user in your table you should see emails appear in your SendGrid logs. users Thats it! Conclusion The concept of broadcasting events directly from your database isn’t something new and as a result this type of functionality is available to you in any language and framework. But! The core features and functionality of Elixir and Phoenix make using database events much easier and more reasonable than I have found in any other system. Pattern Matching and OTP principles are both simple and powerful and I encourage anyone to take a deep dive into them when possible. 🧞 This is open source! you can find it here on Github ❤️ I only write about programming and remote work. If you I won’t waste your time. follow me on Twitter
