1. Understand why programmers need to work with APIs
2. Learn some of the basic ways in which programmers work with APIs

An API, or application programming interface, is a manner in which companies and organizations, like Twitter or the New York City government, expose their data and/or functionality to the public (i.e. talented programmers like yourself) for use. APIs allow us to add important data and functionality to the applications we build. Here's just a few examples of some of the cool things you can do by using APIs:

• Create an app that allows users to sign up/sign in via Facebook/Google/Twitter/Github/etc.
• Use the NYC Open Data API to get and map data––everything from Health Department restaurant ratings to public park locations and hours to New York City Public Housing repair issues to noise complaints to public school construction, you name it!
• Use the Yelp API to find and deliver popular local spots to your users.
• Use the Weather Underground API to give your users up-to-date weather alerts.
• Use the Ticket Master API to inform your users if their favorite musician has an upcoming show.
• So much more!

This is just a small sample of what working with APIs allows us to do as developers. Throughout the course of your programming life, you'll likely be exposed to working with many different APIs. You'll even learn how to build your own API later on in this course. This reading seeks to introduce the topic, emphasize some of the benefits of getting comfortable working with APIs and offer a brief intro into some of the common methods of working with APIs.

Different APIs expose their data and functionalities in different ways. However, there are commonalities among them and there are common approaches that we'll discuss here. Generally speaking, there are two main uses for APIs––getting data and adding functionality (i.e. signing in with Facebook or posting to Instagram). We'll be discussing the "getting data" part of working with APIs here.

Many APIs are built on what is referred to as a REST-ful framework. That means that the "endpoints", or URLs to which we can send a request for data, follow certain conventions. These URLs should allow you to request information, send information, update information and delete information. Let's focus on the "getting information" request.

For this walk-through, we'll be working with the NYC Open Data API. Let's say we've been hired by the city to create an app that will help parents sign their children up for after-school activities. To connect parents to after-school clubs around the city, we need a data set of such clubs. Luckily for us, the city has collected that information and allows the public to access it via their Open Data API. Let's check out the documentation for their after-school club data set.

Take a few minutes and familiarize yourself with resource linked to above. Learning how to read API documentation is an important skill. It's okay if you don't understand everything in the above document. For now, just look it over briefly.

As you read through, you'll see that the documentation lists the API endpoint. Endpoint refers to the URL we can submit a request to and that will return to us the desired data.

Open up a new tab in your browser and paste in the following URL: http://data.cityofnewyork.us/resource/uvks-tn5n.json

The page brings you to is the desired set of data! Notice that the data is laid out in what looks like a big array of nested hashes. This is actually a JSON object, which behaves just like a Ruby hash. Working with the JSON data returned to you by requests to an API is one of the reasons why we spent so much time in previous lessons learning how to manipulate and operate on nested hashes.

Top Tip: Once you find the right URL for retrieving your data, test it out directly in your browser before you try to request the data from inside your program. If pasting the URL into your browser brings you to the right data, you can move on. This cuts down on debugging time. This way, once you try to request the data from within your program, if it doesn't work, at least you'll know it's something wrong with your code, as opposed to something wrong with the API.

Now that we understand what an API is and have even dealt with a URL that takes us to a real API endpoint, let's use that same URL to send a request for data from a Ruby program. Fork and clone this repo locally.

Open up lib/nyc_api.rb. Let's take a look at the code here:

require 'net/http'
require 'open-uri'
require 'json'

class GetPrograms

  URL = "http://data.cityofnewyork.us/resource/uvks-tn5n.json"

  def get_programs
    uri = URI.parse(URL)
    response = Net::HTTP.get_response(uri)
    response.body
  end

end

programs = GetPrograms.new.get_programs
puts programs

We stored our API endpoint URL in a constant at the top of our class. Then, we have a get_programs method that uses the NET::HTTP library to send an HTTP request from our program. NET::HTTP is a Ruby library that allows your program or application to send HTTP requests. We require it at the top of our file with the require statement. We also require the URI library which helps Ruby to handle URIs.

Both NET::HTTP and URI are classes built into Ruby. Check out the links at the bottom of this lesson to read more about their usage. Don't worry too much about NET::HTTP and URI right now, though. Just focus on getting a basic understanding of and exposure to the tools we can use inside our applications to request data from an API.

A Note on Requirements: We can use require statements to include libraries of code in our own programs. We can require libraries like NET::HTTP, or we can require gems, like Pry.

Now, in your terminal in the directory of this lab, run ruby lib/nyc_api.rb. It should output the JSON response from the NYC Open Data API!

Now that we have all of our data back from the API, we need to be able to collect and present it within the context of our app. Since we are basically pros at manipulating nested hashes, we shouldn't have too much trouble. Let's write a method, program_school, that just returns a list of the schools or organizations that are running our after school programs.

Copy and paste the following code into our GetPrograms class:

def program_school
# we use the JSON library to parse the API response into nicely formatted JSON
  programs = JSON.parse(self.get_programs)
  programs.collect do |program|
    program["agency"]  
  end
end

At the bottom of the file, comment out:

programs = GetPrograms.new.get_programs
puts programs

Let's puts out a unique list of the schools. Paste in the following two lines right underneath where you commented out the above two lines:

programs = GetPrograms.new
puts programs.program_school.uniq

Now, run the program with ruby lib/nyc_api.rb in your terminal. You should see something like this:

Rockaway Artist Alliance, Inc.
CAMBA  
Sports and Arts In Schools Foundation, Inc.
New York Junior Tennis League
Arthur Ashe Institute for Urban Health, Inc
Citizens Advice Bureau, Inc.
United Activities Unlimited, Inc.
Kips Bay Boys & Girls Club
National Society For Hebrew Day Schools
School Settlement
The Door - A Center of Alternatives
Community Counseling and Mediation
Dream Yard Project, Inc.
The Childrens Aid Society
Just Us, Inc.
Bushwick Community Action Association, Inc.
Greater Ridgewood Youth Council, Inc.
Brooklyn Bureau of Community Services
...

So far we've used the NET::HTTP and URI to send a request for data to an API endpoint, a URL. We've operated on the data that was returned to us, making sure it was formatted properly as JSON and iterating over that JSON to retrieve the name of the school hosting each after-school program. That was a lot of work! I wonder if there is an easier way to work with popular APIs...

Many popular APIs have wrappers, i.e. gems that are code libraries that do a lot of the heavy lifting for you. In fact, we'll use a gem to interact with the Twitter API in the next lab.

To recap: APIs generally either provide a user with data or added functionality. We can use APIs that serve data to get information for our own applications and projects. To get this data, we need to send a request to the URL of the API and know how to work with the response we receive. Many APIs serve data in JSON format, which needs to be parsed before we can use it. Once parsed, it becomes a hash we can work with and extract data from.

In our example, we were able to retrieve remote information from an API using the built-in Ruby classes NET::HTTP and URI. By putting this implementation inside a class, we can develop highly reuseable code that lets us access all sorts of information remotely.

The GetPrograms class used a hard-coded URL, stored as a class constant, and included an instance method called get_programs:

URL = "http://data.cityofnewyork.us/resource/uvks-tn5n.json"

def get_programs
  uri = URI.parse(URL)
  response = Net::HTTP.get_response(uri)
  response.body
end

But we could easily adapt this code to be flexible and accept any URL we pass in using an initialize method and an instance variable. The get_programs method is really just getting the response body from the requested URL, so we could name this get_response_body to be more accurate. We could replace the custom program_school method with a general parse_json method, as well. Instead of a specific class, we would instead have a class that retrieves JSON from any provided URL!

• NET::HTTP
• Open URI