07_test_driving_write_operations.md

Test-driving write operations

This is a Makers Vine. Vines are designed to gradually build up sophisticated skills. They contain a mixture of text and video, and may contain some challenge exercises without proposed solutions. Read more about how to use Makers Vines.

Learn to test-drive "Repository" class methods to INSERT, DELETE and UPDATE.

Demonstration

Here's a video demonstration of designing the create, delete and update methods.

The create method

The process to follow is the same you used for the previous methods — but the operation we want to implement is to insert new records.

Here is a design for the create method of the example class StudentRepository:

Method	Job	Arguments	SQL query	Returns
create	Insert a student	A Student object	INSERT INTO students (name, cohort_name) VALUES ($1, $2);	-

As the INSERT query contains some dynamic parts (the new values to insert), we need to use SQL parameters as well.

INSERT INTO students (name, cohort_name) VALUES ($1, $2);

Here is the expected behaviour for the method:

repository = StudentRepository.new

# Build a new model object
student = Student.new
student.name = 'Alice'
student.cohort_name = 'February 2022'

repository.create(student) # Performs the INSERT query

# Performs a SELECT query to get all records (implemented previously)
all_students = repository.all 

# all_students should contain the student 'Alice' created above.

The delete method

The design of the delete method is similar to the find method previously implemented — taking an ID as an argument. However, it runs a DELETE SQL query to delete a specific row.

Method	Job	Arguments	SQL query	Returns
delete	Delete a student	A (numeric) id	DELETE FROM students WHERE id = $1;	-

Here is the expected behaviour for the method:

repository = StudentRepository.new

# Delete the student with id=1
repository.delete(1)

repository.all # The student with id=1 should now be removed.

Exercise

Work in the project directory music_library you've worked on before.

Test-drive the method .create on the class AlbumRepository from the previous project music_library.

repository = AlbumRepository.new

album = Album.new
album.title = 'Trompe le Monde'
album.release_year = 1991
album.artist_id = 1

repository.create(album)

all_albums = repository.all

# The all_albums array should contain the new Album object

1. Encode the expected behaviour above as a new test for the AlbumRepository class.
2. Implement the .create method to make this test pass.

Example solution

Challenge

This is a process feedback challenge. That means you should record yourself doing it and submit that recording to your coach for feedback. How do I do this?

This is a big one! To work on this challenge, first:

• Setup a new project directory social_network.
• Create a new database social_network.

Then:

1. Design the two tables for the following user stories.

   As a social network user,
   So I can have my information registered,
   I'd like to have a user account with my email address.
   
   As a social network user,
   So I can have my information registered,
   I'd like to have a user account with my username.
   
   As a social network user,
   So I can write on my timeline,
   I'd like to create posts associated with my user account.
   
   As a social network user,
   So I can write on my timeline,
   I'd like each of my posts to have a title and a content.
   
   As a social network user,
   So I can know who reads my posts,
   I'd like each of my posts to have a number of views.
   

2. Test-drive the Model and Repository classes for these two tables.

   • You should end up with two Model classes and two Repository classes.
   • You should test-drive and implement the four methods all, find, create and delete for each Repository class.

3. If you'd like an extra challenge, test-drive as well an update method for both classes, which updates a specific record.

After you're done, submit your recording here.

Next Challenge

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