Rails CheatSheet

Migrations

1. Generate a Migration

rails generate migration CreateUsers
# or
rails g migration CreateUsers

2. Create a Table

create_table :products do |t|
  t.string :name
  t.float :price

  t.timestamps
end

Supported column types: :boolean :date :datetime :float :integer :string :text :time

Common Methods for Changing Tables

add_column :table_name, :column_name, :type, options_hash
remove_column :table_name, :column_name
rename_column :table_name, :old_column_name, :new_column_name
rename_table :old_table_name, :new_table_name
add_index :table_name, %i[column1 column2], options_hash
change_column :table_name, :column_name, :type, options_hash

Additional Table Examples

# Make the id a UUID
create_table :places, id: :uuid do |t|
  t.string :name, null: false
  t.string :address, null: false
  t.string :city, null: false

  t.timestamps
end

# Use references for a foreign key

# Using decimals, for a decimal value, set a scale (num of digits after period) and precision (total numbers)

create_table :internet_speeds, id: :uuid do |t|
  t.references :place, null: false, foreign_key: true, index: true, type: :uuid
  t.decimal :download_speed, null: false, scale: 2, precision: 10
  t.string :download_units, null: false

  t.timestamps
end

3. Create a table by running your migration

Edit a migration by running a new migration to make changes to your table. Don’t edit after migration.

rails db:migrate

Models

Associations

Example of has_many, belongs_to, and has_many_through:

class Physician < ApplicationRecord
  has_many(
    :appointments,
    class_name: 'Appointment',
    foreign_key: :physician_id,
    primary_key: :id
  )

  has_many :patients, through: :appointments, source: :patient
end

class Appointment < ApplicationRecord
  belongs_to(
    :physician,
    class_name: 'Physician',
    foreign_key: :physician_id,
    primary_key: :id
  )

  belongs_to(
    :patient,
    class_name: 'Patient',
    foreign_key: :patient_id,
    primary_key: :id
  )
end

class Patient < ApplicationRecord
  has_many(
    :appointments
    class_name: 'Appointment',
    foreign_key: :patient_id,
    primary_key: :id
  )

  has_many :physicians, through: :appointments, source: :physician
end

Ensure that a belongs_to is deleted when its has_many is destroyed with dependent: :destroy

class Patient < ApplicationRecord
  has_many(
    :appointments
    class_name: 'Appointment',
    foreign_key: :patient_id,
    primary_key: :id,
    dependent: :destroy
  )

Validation

Validations are defined inside models. Constraints are defined inside migrations.

Common validations:

presence: true
uniqueness: true

Restrict validation with scope:

class Holiday < ApplicationRecord
  # no two Holidays with the same name for a single year
  validates :name,
            uniqueness: {
              scope: :year,
              message: "should happen once per year"
            }
end

Validate that a value is one of allowed possible values:

validates :status,
          inclusion: {
            in: "PENDING APPROVED DENIED",
            message: "%<value>% is not a valid status"
          }

Zach Grammon