Create Model Class and Migrate Database

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Task

• Generate a new model class, Person (as per the class diagram below), and initialize the database for saving Person objects.

Steps

Pre-Task Steps

Inspect model files and folders:

• app/models/ - folder where model classes go (currently empty).
• app/models/application_record.rb - a base class inherited by all model classes.

Inspect database tables:

psql --command="\dt" app_development

• Lists only two default tables, ar_internal_metadata and schema_migrations.
• ⚠️ Press Q key to quit if command locks terminal.

Task Steps

Generate model class Person and database migration script:

rails generate model Person first_name:string last_name:string height_inches:integer weight_lbs:integer

Run migration to configure database:

rails db:migrate:reset

Post-Task Steps

Inspect the database tables:

psql --command="\dt" app_development

• Now includes people table.
• Table name is plural snake_case form of class name (Person class → people table).
• ⚠️ Press Q key to quit if command locks terminal.

Inspect schema of people table:

psql --command="\d people" app_development

• Includes attribute columns, first_name and last_name.
• Includes id, a unique ID number for each row.
• Includes created_at and updated_at, automatically generated timestamps.
• ⚠️ Press Q key to quit if command locks terminal.

Inspect rows of people table:

psql --command="SELECT * FROM people" app_development

• Currently has 0 rows.
• ⚠️ Press Q key to quit if command locks terminal.

Inspect generated migration:

• db/migrate/20240203174351_create_people.rb - migration script for setting up database.
  • Contains call to create_table for adding new table to database.
  • Numbers in file name are timestamp indicating when file was generated.

Inspect generated model class:

• app/models/person.rb - code file to open in VS Code.
  • Class Person definition empty because Rails automatically generates attributes based on db/schema.rb.
  • Annotate-generated comments list attributes.

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