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Migrate a rails project to use uuids
# Inspired by
task id_to_uuid: :environment do
puts "[START] Convert id to uuid"
ActiveRecord::Base.connection.enable_extension 'uuid-ossp' unless ActiveRecord::Base.connection.extensions.include? 'uuid-ossp'
ActiveRecord::Base.connection.enable_extension 'pgcrypto' unless ActiveRecord::Base.connection.extensions.include? 'pgcrypto'
table_names = ActiveRecord::Base.connection.tables - ["schema_migrations", "ar_internal_metadata", "migration_validators"]
table_names.each do |table_name|
puts "[CREATE] uuid column for #{table_name}"
#Make sure the column is a uuid if not delete it and then create it
if ActiveRecord::Migration.column_exists? table_name, :uuid
column_type = ActiveRecord::Migration.columns(table_name).select{|c| == "uuid"}.try(:first).try(:sql_type_metadata).try(:type)
if column_type && column_type != :uuid
ActiveRecord::Migration.remove_column(table_name, :uuid)
# Create it if it doesn't exist
if !ActiveRecord::Migration.column_exists? table_name, :uuid
ActiveRecord::Migration.add_column table_name, :uuid, :uuid, default: "uuid_generate_v4()", null: false
# The strategy here has three steps.
# For each association:
# 1) write the association's uuid to a temporary foreign key _uuid column,
# 2) For each association set the value of the _uuid column
# 3) remove the _id column and
# 4) rename the _uuid column to _id, effectively migrating our foreign keys to UUIDs while sticking with the _id convention.
table_names.each do |table_name|
puts "[UPDATE] change id to uuid #{table_name}"
model = table_name.singularize.camelize.constantize
id_columns ={|c| c.end_with?("_id")}
# write the association's uuid to a temporary foreign key _uuid column
# eg. Message.room_id => Message.room_uuid
model.reflections.each do|k, v|
association_id_col = v.foreign_key
# Error checking
# Make sure the relationship actually currently exists
next unless id_columns.include?(association_id_col)
# Check that there is at
# 1) Create temporary _uuid column set to nulll,
tmp_uuid_column_name = column_name_to_uuid(association_id_col)
unless ActiveRecord::Migration.column_exists?(table_name, tmp_uuid_column_name)
puts "[CREATE] #{table_name}.#{tmp_uuid_column_name}"
ActiveRecord::Migration.add_column(table_name, tmp_uuid_column_name, :uuid)
# 2) For each association set the value of the _uuid column
# For example. Assume the following example
# message.room_id = 1
# room = Room.find(1)
# room.uuid = 0x123
# message.room_uuid = 0x123
association_klass = v.klass
model.unscoped.all.each do |inst|
next unless inst.present?
association = association_klass.find_by(id: inst.try(association_id_col.try(:to_sym)))
next unless association.present?
inst.update_column(tmp_uuid_column_name, association.try(:uuid))
# 3) Remove id column
ActiveRecord::Migration.remove_column table_name, association_id_col if ActiveRecord::Migration.column_exists?(table_name, association_id_col)
# 4) Rename uuid_col_name to id
ActiveRecord::Migration.rename_column table_name, tmp_uuid_column_name, association_id_col
rescue => e
puts "Error: #{e} continuing"
# Make each temp _uuid column linked up
# eg. Message.find(1).room_uuid = Message.find(1).room.uuid
puts "[UPDATE] #{model}.uuid to association uuid"
## Migrate primary keys to uuids
table_names.each do |table_name|
if ActiveRecord::Migration.column_exists?(table_name, :id) && ActiveRecord::Migration.column_exists?(table_name, :uuid)
ActiveRecord::Base.connection.execute %Q{ALTER TABLE #{table_name} DROP CONSTRAINT #{table_name}_pkey CASCADE} rescue nil
ActiveRecord::Migration.remove_column(table_name, :id)
ActiveRecord::Migration.rename_column( table_name, :uuid, :id) if ActiveRecord::Migration.column_exists?(table_name, :uuid)
ActiveRecord::Base.connection.execute "ALTER TABLE #{table_name} ADD PRIMARY KEY (id)"
ActiveRecord::Base.connection.execute %Q{DROP SEQUENCE IF EXISTS #{table_name}_id_seq CASCADE} rescue nil
# Add uuid to the id
# EG. column_name_to_uuid("room_id") => "room_uuid"
# EG. column_name_to_uuid("room_ids") => "room_uuids"
def column_name_to_uuid(column_name)
*a, b = column_name.split("_id", -1)
a.join("_id") + "_uuid" + b
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