Added check for add_exclusion_constraint - closes #191

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## 1.4.0 (unreleased)
 
+- Added check for `add_exclusion_constraint`
 - Added support for `RACK_ENV`
 - Fixed error when `Rails` defined without `Rails.env`
 - Fixed error with `change_column_null` when table does not exist

README.md

@@ -74,6 +74,7 @@ Postgres-specific checks:
 - [adding an index non-concurrently](#adding-an-index-non-concurrently)
 - [adding a reference](#adding-a-reference)
 - [adding a foreign key](#adding-a-foreign-key)
+- [adding an exclusion constraint](#adding-an-exclusion-constraint) [unreleased]
 - [adding a json column](#adding-a-json-column)
 - [setting NOT NULL on an existing column](#setting-not-null-on-an-existing-column)
 
@@ -488,6 +489,24 @@ class ValidateForeignKeyOnUsers < ActiveRecord::Migration[7.0]
 end
 ```
 
+### Adding an exclusion constraint
+
+#### Bad
+
+In Postgres, adding an exclusion constraint blocks reads and writes while every row is checked.
+
+```ruby
+class AddExclusionContraint < ActiveRecord::Migration[7.1]
+  def change
+    add_exclusion_constraint :users, "number WITH =", using: :gist
+  end
+end
+```
+
+#### Good
+
+[Let us know](https://github.com/ankane/strong_migrations/issues/new) if you have a safe way to do this (exclusion constraints cannot be marked `NOT VALID`).
+
 ### Adding a json column
 
 #### Bad

lib/strong_migrations/checker.rb

@@ -36,6 +36,8 @@ def perform(method, *args)
           check_add_check_constraint(*args)
         when :add_column
           check_add_column(*args)
+        when :add_exclusion_constraint
+          check_add_exclusion_constraint(*args)
         when :add_foreign_key
           check_add_foreign_key(*args)
         when :add_index

lib/strong_migrations/checks.rb

@@ -73,6 +73,14 @@ def check_add_column(*args)
       end
     end
 
+    def check_add_exclusion_constraint(*args)
+      table = args[0]
+
+      unless new_table?(table)
+        raise_error :add_exclusion_constraint
+      end
+    end
+
     # unlike add_index, we don't make an exception here for new tables
     #
     # with add_index, it's fine to lock a new table even after inserting data

lib/strong_migrations/error_messages.rb

@@ -231,7 +231,10 @@ def change
 
     validate_check_constraint:
 "Validating a check constraint while writes are blocked is dangerous.
-Use disable_ddl_transaction! or a separate migration."
+Use disable_ddl_transaction! or a separate migration.",
+
+    add_exclusion_constraint:
+"Adding an exclusion constraint blocks reads and writes while every row is checked."
   }
   self.enabled_checks = (error_messages.keys - [:remove_index]).map { |k| [k, {}] }.to_h
 end

test/add_exclusion_contraint_test.rb

@@ -0,0 +1,16 @@
+require_relative "test_helper"
+
+class AddExclusionConstraintTest < Minitest::Test
+  def setup
+    skip unless ActiveRecord::VERSION::STRING.to_f >= 7.1
+    super
+  end
+
+  def test_basic
+    assert_unsafe AddExclusionConstraint
+  end
+
+  def test_new_table
+    assert_safe AddExclusionConstraintNewTable
+  end
+end

test/migrations/add_exclusion_constraint.rb

@@ -0,0 +1,15 @@
+class AddExclusionConstraint < TestMigration
+  def change
+    add_exclusion_constraint :users, "credit_score WITH =", using: :gist
+  end
+end
+
+class AddExclusionConstraintNewTable < TestMigration
+  def change
+    create_table :new_users do |t|
+      t.decimal :credit_score, precision: 10, scale: 5
+    end
+
+    add_exclusion_constraint :new_users, "credit_score WITH =", using: :gist
+  end
+end

test/test_helper.rb

@@ -40,6 +40,9 @@ def schema_migration
 ActiveRecord::Schema.define do
   enable_extension "citext" if $adapter == "postgresql"
 
+  # for exclusion constraints
+  enable_extension "btree_gist" if $adapter == "postgresql"
+
   # for gen_random_uuid() in Postgres < 13
   enable_extension "pgcrypto" if $adapter == "postgresql"