(Rails5) Use Scoped Uniqueness Validations

Consider this: we have an aggregation app, that receives data from other apps.

class Event < ApplicationRecord
  # Scheme  
  # t.integer :origin_app, null: false, default: 0, index: true
  # t.integer :origin_type, null: false, default: 0, index: true
  # t.integer  :origin_id, null: false, index: true  

  enum origin_app: { old_app: 0, new_app: 1 }
  enum origin_type: { good: 0, bad: 1 }

  validates :origin_app, :origin_type, :origin_id, presence: true
end

We want to validate :origin_id uniqueness within an app and type.

1. DB Level

Add a compound uniqueness index in migration.

# add_index :<table>, [:<validatable field>, :<scope_field_1>, .. , :<scope_field_n>], unique: true

# e.g.
add_index :admin_events, [:origin_id, :origin_app, :origin_type], unique: true

# NB, sometimes these compound indice names can get too long, use
add_index :admin_events, [:origin_id, :origin_app, :origin_type], unique: true, name: "idx_admin_event_origin_origin_app_origin_type"

# The logic would be:

# index becomes idx
# singular table name
# no joining words
# no _id
# alphabetical order

2. App Level

Add a uniqueness validation with scope option.

class Event < ApplicationRecord  
  # ...
  validates :origin_id, uniqueness: {scope: [:origin_app, :origin_type]}  
end

Troubleshooting

Consult the docs.

job

Written on May 26, 2016