Iteration 0 - Initial Structure

For our first iteration, we’re going to build out a complete “slice” of project functionality across several of our data files. For this iteration, the slice we’ll be focusing on deals with Enrollment data by district.

To complete the iteration, we’ll need to achieve the following:

1. Provide a top-level interface to query for information by District name
2. Create basic domain objects for the District and Enrollment data
3. Construct appropriate relationships between Districts and underlying Enrollment data
4. Use these domain objects to answer some basic analytical questions about enrollment by district.

Data Access Layer

DistrictRepository

The DistrictRepository is responsible for holding and searching our District instances. It offers the following methods:

• #find_by_name - returns either nil or an instance of District having done a case insensitive search
• #find_all_matching - returns either [] or one or more matches which contain the supplied name fragment, case insensitive

There is no one data file that contains just the districts. The data must be extracted from one of the other files. Let’s use Kindergartners in full-day program.csv so the instance is created and used like this:

dr = DistrictRepository.new
dr.load_data({
  :enrollment => {
    :kindergarten => "./data/Kindergartners in full-day program.csv"
  }
})
district = dr.find_by_name("ACADEMY 20")
# => <District>

District

The District is the key concept in our data hierarchy. It starts with just one method:

• #name - returns the upcased string name of the district

We create an instance like this:

d = District.new({:name => "ACADEMY 20"})

EnrollmentRepository

The EnrollmentRepository is responsible for holding and searching our Enrollment instances. It offers the following methods:

• #find_by_name - returns either nil or an instance of Enrollment having done a case insensitive search

For iteration 0, the instance of this object represents one line of data from the file Kindergartners in full-day program.csv. It’s initialized and used like this:

er = EnrollmentRepository.new
er.load_data({
  :enrollment => {
    :kindergarten => "./data/Kindergartners in full-day program.csv"
  }
})
enrollment = er.find_by_name("ACADEMY 20")
# => <Enrollment>

Enrollment

An Enrollment instance holds the enrollment data for a single district. We create an instance like this:

e = Enrollment.new({:name => "ACADEMY 20", :kindergarten_participation => {2010 => 0.3915, 2011 => 0.35356, 2012 => 0.2677}})

An instance of this class offers the following methods:

#kindergarten_participation_by_year

This method returns a hash with years as keys and a truncated three-digit floating point number representing a percentage for all years present in the dataset.

Example:

enrollment.kindergarten_participation_by_year
=> { 2010 => 0.391,
     2011 => 0.353,
     2012 => 0.267,
   }

#kindergarten_participation_in_year(year)

This method takes one parameter:

• year as an integer for any year reported in the data

A call to this method with any unknown year should return nil.

The method returns a truncated three-digit floating point number representing a percentage.

Example:

enrollment.kindergarten_participation_in_year(2010) # => 0.391