Database folder and migrations in Ruby on Rails - Step-by-Step Execution

Concept Flow - Database folder and migrations

Create Migration File

↓

Write Schema Changes

↓

Run Migration Command

↓

Rails Updates Schema

↓

Database Structure Changes

↓

Migration Status Updated

Shows how a migration file is created, written, run, and applied to update the database schema.

Execution Sample

Ruby on Rails

class CreateUsers < ActiveRecord::Migration[7.0]
  def change
    create_table :users do |t|
      t.string :name
      t.timestamps
    end
  end
end

This migration creates a users table with a name column and timestamps.

Execution Table

Step	Action	File/Command	Effect	Database State
1	Generate migration file	rails generate migration CreateUsers	Creates db/migrate/xxxx_create_users.rb	No users table yet
2	Write migration code	db/migrate/xxxx_create_users.rb	Defines users table with name and timestamps	No change yet
3	Run migration	rails db:migrate	Rails runs migration code	Users table created with columns: id, name, created_at, updated_at
4	Update schema.rb	Automatic	Schema file updated to reflect new table	Schema matches database
5	Migration status	rails db:migrate:status	Shows migration as up	Migration applied successfully
6	Exit	-	No more migrations to run	Database schema up to date

💡 All migrations applied, database schema is current

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
users_table	does not exist	migration file created	table created in DB	table exists with columns

Key Moments - 2 Insights

Why doesn't the database change immediately after creating the migration file?

Creating the migration file only prepares the instructions. The database changes only after running 'rails db:migrate' as shown in step 3 of the execution_table.

What does the schema.rb file represent?

schema.rb is an auto-generated file that reflects the current database structure after migrations run, as seen in step 4 of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is the users table actually created in the database?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Check the 'Effect' and 'Database State' columns for when the table appears

According to variable_tracker, what is the state of users_table after step 1?

A Migration file created but table does not exist

B Table exists with columns

C Table created in DB

D No users table yet

💡 Hint

Look at the 'After Step 1' column for users_table

If you skip running 'rails db:migrate', what will happen to the database?

A Database schema updates automatically

B Database remains unchanged

C Schema.rb updates but DB does not

D Migration status shows as up

💡 Hint

Refer to step 3 and the exit_note in execution_table

Concept Snapshot

Database folder holds migration files.
Migrations describe schema changes.
Run 'rails db:migrate' to apply changes.
Schema.rb reflects current DB structure.
Migration status shows applied migrations.

Full Transcript

In Rails, the database folder contains migration files that describe changes to the database structure. First, you generate a migration file which is just a set of instructions. Then you write the schema changes inside it, like creating tables or adding columns. When you run 'rails db:migrate', Rails executes these instructions and updates the actual database. After migration, Rails updates the schema.rb file to reflect the current database structure. You can check migration status to see which migrations have been applied. This process ensures your database matches your app's needs step-by-step.