Adding and removing columns in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What command do you use to add a new column to an existing table in Rails?

You create a migration with rails generate migration AddColumnNameToTableName column_name:data_type and then run rails db:migrate.

beginner

How do you remove a column from a table in Rails migrations?

Use remove_column :table_name, :column_name inside a migration and then run rails db:migrate.

beginner

What is the purpose of the change method in a Rails migration?

The change method defines what changes to make to the database schema. Rails can automatically reverse these changes when rolling back.

intermediate

Why should you avoid adding columns directly in the database without migrations in Rails?

Because migrations keep your schema consistent and track changes, making it easier to share and rollback changes safely.

beginner

What data types can you specify when adding a column in Rails migrations?

Common types include :string, :text, :integer, :boolean, :datetime, and :float.

Which Rails command generates a migration to add a column?

A rails generate migration AddAgeToUsers age:integer

B rails add column age to users

C rails db:add_column age users

D rails create column age users

The correct syntax is to generate a migration with the name describing the change, like AddAgeToUsers, and specify the column and type.

How do you remove a column named 'email' from the 'customers' table in a migration?

A remove :customers, :email

B remove_column :customers, :email

C delete_column :customers, :email

D drop_column :customers, :email

The correct method is remove_column with the table name and column name as arguments.

What happens if you run rails db:rollback after adding a column with a migration?

A The migration file is deleted

B Nothing happens

C The entire table is deleted

D The added column is removed from the table

Rollback reverses the last migration, so the added column will be removed.

Which method inside a migration allows Rails to automatically reverse changes?

A down

B up

C change

D migrate

The change method lets Rails know how to apply and reverse the migration automatically.

Why is it important to use migrations for schema changes in Rails?

A To keep schema changes tracked and reversible

B To speed up the app

C To avoid writing Ruby code

D To prevent database backups

Migrations track changes and allow safe rollbacks, keeping the database schema consistent.

Explain the steps to add a new column to an existing table in Rails using migrations.

Think about how Rails tracks database changes safely.

Describe how Rails migrations help manage database schema changes like adding or removing columns.

Consider why direct database edits can be risky.