Vent

Vent is a Microblogging (twitter-like) application. The purpose of this tutorial is to learn the basics of Clojure, with some guidance from a tutor.

Table of Contents

• Start the project
• Application Structure
  • Vent
  • User
• Challenges
  • Fetch database vents
  • Implement Add Vent
  • Implement favorites list
  • Add author to vents
  • Implement Following page
  • Implement Followers page
  • Implement (un)Follow Button
  • Implement toggle favorite button

Start the project

1. Clone edge and go into the tutorial

   $ git clone https://github.com/juxt/edge.git
   $ cd edge/examples/tutorial.vent

2. Start a REPL

   $ ../bin/rebel --cljs -A:dev:build:dev/build

3. Start the server

   dev=> (go)

There is a front-end you can browse at http://localhost:3000.

Application Structure

In src/tutorial/vent/lib.clj there are a number of functions which haven’t yet been implemented. The majority of challenges require:

1. Fetching information from a "db" (A file on disk)

2. Manipulating that data

3. Writing new data to the db

There are 3 operations for the database:

(db/reset)

This will reset the database to a known good state

(db/store new-db)

Save a new version of the database

(db/read)

Fetch the current version of the database

These are available in your REPL.

Vent

Vents are stored in the database as a sequence. Each Vent has these keys:

:id	A globally unique id for this message, a number works.
:text	The text of the actual vent
:username	The username of the author, a string.
:favorite?	(Optional) Either true or false, dictates where the tweet is a favorite.
:author	(Optional) The data of the User (see below) who created it. This should be added after reading from the database, it should not be stored in the database.

An example Vent in the database

{:id 2
 :text "Lord but I dislike poetry. How can anyone remember words that aren't put to music?"
 :username "arl_the_bard"
 :favorite? true}

An example Vent with an author attached

{:id 2
 :text "Lord but I dislike poetry. How can anyone remember words that aren't put to music?"
 :author {:name "Arliden"
          :following? true}
 :username "arl_the_bard"
 :favorite? true}

How Vents look in the database

{:vents [{:id 1 :text "Text" :username "foo"} …]}

User

Users are stored in the database as a map. This is like a dictionary or hash map in other languages. The keys are usernames, and the values are Users.

Users look like so:

:name	A full name
:follows	A list of usernames this user follows
:following?	(Optional) true or false, defaults to false. Whether or not the user is being followed

An example user

{:name "John Smith"
 :follows ["janesmith" "arl_the_bard"]
 :following? false}

How users are stored in the database

{:users {"jsmith" {:name "John Smith"
                   :follows ["janesmith" "arl_the_bard"]
		   :following? true}
         "arl_the_bard" {:name "Arliden"
	                 :follows ["janesmith"]}}}

Challenges

These can all be achieved by modifying files in src/tutorial/vent/lib.clj.

Fetch database vents

Currently, the vents from all are hard-coded. It would be great if all would return all the vents from the database.

Tip	Use (db/read) and get the :vents key out of it.

Implement Add Vent

Add the ability to create a new vent.

Tip	update the :vents in the database with conj. Use the generate-id function to create an id for the vent.

Implement favorites list

Take the list of vents in the database, and filter them to show only the favorites on the favorites page.

Tip	Use filter and anonymous functions to filter the list of vents.

Add author to vents

Depends on Fetch database vents.

Now that vents are being fetched from the database, the user details are missing! Fetch the user information from the database based on the :username key in the vent, and add it to the vents as the :author key.

Tip	Use map to modify each of the vents with assoc, and get-in to get the corresponding user from the database.

Implement Following page

Add the ability to see who you follow.

Tip	select-keys over users in your :follows key.

Implement Followers page

Add the ability to see who your followers are.

Tip	select-keys on users, based on a keep on the :users which have username in their :follows.

Implement (un)Follow Button

You will need to complete Implement Followers page to see this working.

Make it so that Follow/Unfollow buttons toggle the current state.

Tip	update-in the database and conj in the new username.

Implement toggle favorite button

You won’t be able to see this working until you’ve done Implement favorites list.

Add the ability for the user to make a vent a favorite.

Tip	Use map and check using = if the current vent is the one you’re supposed to update. You might want to https://clojuredocs.org/clojure.core/not the current value.