Class: RuboCop::Cop::Discourse::NoAddReferenceOrAliasesActiveRecordMigration

Inherits:
Base
  • Object
show all
Defined in:
lib/rubocop/cop/discourse/no_add_reference_active_record_migrations.rb

Overview

The methods:

  • add_reference

  • add_belongs_to

  • t.references

  • t.belongs_to

in ActiveRecord migrations are magic, and they all do some unexpected things in the background. For example, by default add_reference adds an index at the same time, but not concurrently, which is a nightmare for large tables.

Instead, inside a disable_ddl_transaction! migration we should create the new column (with any defaults and options required) and the index concurrently using hand-written SQL. This also allows us to handle IF NOT EXISTS cases, which enable re-runnable migrations. Also we can pick a better name for the index at the same time.

# bad def up

add_reference :posts, :image_upload
# or add_belongs_to :posts, :image_upload
# or t.references :image_upload when doing create_table do |t|
# or t.belongs_to :image_upload when doing create_table do |t|

end

# good disable_ddl_transaction! def up

execute "ALTER TABLE posts\nADD COLUMN IF NOT EXISTS image_upload_id bigint\n"

execute "CREATE INDEX CONCURRENTLY IF NOT EXISTS\nindex_posts_on_image_upload_id ON posts USING btree (image_upload_id)\n"

end

Constant Summary collapse

MSG = 
"AR methods add_reference, add_belongs_to, t.references, and t.belongs_to are\nhigh-risk for large tables and have too many background magic operations.\nInstead, write a disable_ddl_transactions! migration and write custom SQL to\nadd the new column and CREATE INDEX CONCURRENTLY. Use the IF NOT EXISTS clause\nto make the migration re-runnable if it fails partway through.\n"

Instance Method Summary collapse

Instance Method Details

#on_send(node) ⇒ Object 



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# File 'lib/rubocop/cop/discourse/no_add_reference_active_record_migrations.rb', line 72

def on_send(node)
  if [
       using_add_reference?(node),
       using_add_belongs_to?(node),
       using_t_references?(node),
       using_t_belongs_to?(node),
     ].none?
    return
  end
  add_offense(node, message: MSG)
end