Background and Objectives

Let's code an entire MVC app. We will create an app to save Medium posts and read them later:

As a user, I can list all posts I saved
As a user, I can add a post I want to read later
As a user, I can read a post I saved
As a user, I can mark a post as read

A demo's worth a thousand words, so this is the app we want to code:

List all the saved posts

------------------------------------
Welcome to your Medium pocket reader
------------------------------------

----------------------------
What do you want to do next?
----------------------------
1. List posts
2. Save post for later
3. Read post
4. Mark post as read
5. Exit
> 1

1. [x] - What’s your goal for learning to code? (Boris Paillard)
2. [ ] - Teaching Programming is Hard (Boris Paillard)

Save a post for later

----------------------------
What do you want to do next?
----------------------------
1. List posts
2. Save post for later
3. Read post
4. Mark post as read
5. Exit
> 2

Path?
> le-wagon/this-is-what-a-developer-looks-like-379c261db24d

1. [x] - What’s your goal for learning to code? (Boris Paillard)
2. [ ] - Teaching Programming is Hard (Boris Paillard)
3. [ ] - This is what a developer looks like (Rebecca Menat)

Read a post

----------------------------
What do you want to do next?
----------------------------
1. List posts
2. Save post for later
3. Read post
4. Mark post as read
5. Exit
> 3

1. [x] - What’s your goal for learning to code? (Boris Paillard)
2. [ ] - Teaching Programming is Hard (Boris Paillard)
3. [ ] - This is what a developer looks like (Rebecca Menat)
Index?
> 2

[...] # this should display the post's entire content with linebreaks between paragraphs!

Mark a post as read

----------------------------
What do you want to do next?
----------------------------
1. List posts
2. Save post for later
3. Read post
4. Mark post as read
5. Exit
> 4

1. [x] - What’s your goal for learning to code? (Boris Paillard)
2. [ ] - Teaching Programming is Hard (Boris Paillard)
3. [ ] - This is what a developer looks like (Rebecca Menat)
What index?
> 2

1. [x] - What’s your goal for learning to code? (Boris Paillard)
2. [x] - Teaching Programming is Hard (Boris Paillard)
3. [ ] - This is what a developer looks like (Rebecca Menat)

Exit gracefully

----------------------------
What do you want to do next?
----------------------------
1. List posts
2. Save post for later
3. Read post
4. Mark post as read
5. Exit
> 5

Bye bye!

As you can see, the user only types the path of the Medium article. The path is the text that comes after the domain name in a url.

For instance, to save this article, the path our users need to enter is everything that is after https://medium.com/ i.e. le-wagon/this-is-what-a-developer-looks-like-379c261db24d.

So how are we going to retrieve the post's author, title and content...?

Obviously, we're going to scrape them!

Question: where are we going to code the scraping part?

You'll find the answer at the end of this README.

Specs

Some specs have already been defined. Check all the specs with the rake command or a singol one with rspec spec/spec_name.rb.

Model

As you know now, you should always start with your model. The model is the Ruby class we need in order to manipulate the data in our program.

Here we want to play around with Medium posts, so let's go ahead and create a Post class. Before coding it, take the time to ask yourself about:

Its state:

• What do we need to store in a post to be able to serve the user stories?

The answer will give you the instance variables.

Its behavior:

• What transformations will we need to perform on a post?
• Which pieces of state will we need to expose to reading? To writing?

The answers will give you the public instance methods.

Don't force too much if you can't find all instance variables and methods, you'll find them later when the need emerges while coding the repo and the controller. When you think you're done, test your class in irb, fix bugs, and move on to the next class.

Repository

We need a repository to store our posts in-memory and on our hard drives. This class needs to be coded right after the model, both classes being part of the same data brick.

Implement a Repository class which will act as a fake database. It should be connected to a posts.csv file to make our app persistent.

Controller

The controller serves the user stories. Let's have a look at them:

As a user, I can list all posts I saved
As a user, I can add a post I want to read later
As a user, I can read a post I saved
As a user, I can mark a post as read

Remember that the controller has a role of pivot in the MVC pattern. Having access to the repo and the view from within every action is a necessity (this should help you define instance variables).

For each user story, you need to code an action (an instance method) in the controller.

This is the process you need to follow for each action:

• Write pseudo-code to breakdown the problem in small steps that you can easily translate in ruby
• Remember that each instruction having to do with the data will be delegated to the repo, and every puts and gets will be handled by the view
• Coding your actions will make you code your View class and its instance methods naturally, when the necessity arises
• Every time there's an emerging need (we need a new method in the repo or in the model), follow the flow and code it right away
• Test regularly your code (every 2 or 3 lines of code)

Router

Try to code the router by yourself! Remember that at the end, we want to call router.run in app.rb and this should launch our app!

Tying it all together

We know that the purpose of the app.rb file is to call router.run. This means you need to instantiate a router which is an instance of our Router class. OK so that's a Router.new(controller). That means we need a controller... Following this train of thoughts will lead you to the whole code.

When you are ready, you can run your program with:

ruby lib/app.rb

By the way...

So where should you code the scraping part of the program? Well, let's re-formulate our question. Our program should be able to instantiate a Post with only a path.

But when we instantiate the post, we want it to be automatically populated with its title, content, and author. A good place to code it could be in the Post's initialize method. But that's not where we're going to code it.

Let's imagine that we add an Author model in the picture, and that we want to scrape info about the post's author when scraping the post. The Post#initialize method wouldn't be a good choice anymore... Leaving it in the controller (where we have access to models and repositories) would be a necessity, so let's code it there!