Database schema management in Ruby apps

Database schema management

Vsevolod Romashov Qlean

7even

Migrations

• bin/rails generate migration AddPartNumberToProducts

• bundle exec hanami generate migration create_books

class ChangeDifferentThingsInUsers < ActiveRecord!::Migration def up remove_column :users, :phone change_column_null :users, :email, false add_foreign_key :posts, :users, column: :author_id end

def down remove_foreign_key :posts, column: :author_id change_column_null :users, :email, true add_column :users, :phone, null: false end end

DbSchemahttps://github.com/7even/db_schema

# db/schema.rb DbSchema.describe do |db| db.table :users do |t| t.primary_key :id t.varchar :first_name, null: false t.varchar :last_name t.timestamptz :created_at, default: :'now()' end

db.table :posts do |t| t.primary_key :id t.varchar :title, null: false t.integer :user_id, references: :users

t.index :user_id end end

# lib/db_schema.rb DbSchema.configure( adapter: 'postgresql', host: ENV['db_host'], port: ENV['db_port'], database: ENV['db_name'], user: ENV['db_user'], password: ENV['db_password'] )

load 'db/schema.rb'

Columns• All built-in data types (including extensions) +

custom enum types

• NOT NULL

• Default values (strings, numbers, Date, Time, SQL expressions)

• Type-specific attributes

Indexes• "Common" indexes

• Unique indexes

• Multiple indexes

• Partial indexes

• Expression indexes

• GIN, GiST etc.

• Ordered indexes

Foreign Keys

• Single-column

• Multi-column

• ON DELETE

• ON UPDATE

• Check constraints

• Enum types

• Extensions

DSL ReaderChanges

Runner

Desiredschema

Actualschema Operation

✅ ❌ Create

❌ ✅ Drop

✅ ✅ Change (?)

Create Drop Change

Table ✅ ✅ ✅

Primary Key ✅ ✅

Column ✅ ✅ ✅

Index ✅ ✅ ❗

Foreign Key ✅ ✅ ❗

Check Constraint ✅ ✅ ❗

Change Type ✅

Allow Null ✅

Disallow Null ✅

Change Column Default ✅

Make Column a Primary Key ❌

Drop Primary Key Constraint ❌

Change Column

Create Drop Change

Enum ✅ ✅ ❗

Extension ✅ ✅

Change Enum

Add New Value ✅

Drop Existing Value ❌

Reorder Values ❌

Problems

• Renaming tables & columns

• Some datatype changes

• Adding a NOT NULL column pre-filled with data

• Data migrations

db.migrate do |migration| migration.apply_if do |schema| schema.table(:users).has_field?(:first_name) end

migration.run do |migrator| migrator.create_column :users, :name, :varchar

User.find_each do |user| name = [user.first_name, user.last_name].compact.join(' ') user.update(name: name) end

migrator.drop_column :users, :first_name migrator.drop_column :users, :last_name

migrator.disallow_null :users, :name end end

Roadmap• full-fledged primary keys support

• MySQL/SQLite support

• schema dumper

• model annotations

Questions?