(reversible) rename_constraint helper

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    activerecord-pg-extensions (0.7.0)
+    activerecord-pg-extensions (0.7.1)
       activerecord (>= 7.2, < 8.2)
       railties (>= 7.2, < 8.2)
 

Gemfile.rails-7.2.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    activerecord-pg-extensions (0.7.0)
+    activerecord-pg-extensions (0.7.1)
       activerecord (>= 7.2, < 8.2)
       railties (>= 7.2, < 8.2)
 

Gemfile.rails-8.0.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    activerecord-pg-extensions (0.7.0)
+    activerecord-pg-extensions (0.7.1)
       activerecord (>= 7.2, < 8.2)
       railties (>= 7.2, < 8.2)
 

lib/active_record/pg_extensions/command_recorder.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module PGExtensions
+    # adds support for reverting migration methods added by this gem
+    module CommandRecorder
+      def rename_constraint(table_name, old_name, new_name, **options)
+        record(:rename_constraint, [table_name, old_name, new_name, options])
+      end
+
+      def invert_rename_constraint(args)
+        table_name, old_name, new_name, options = args
+        options ||= {}
+        # flag the trailing hash as keyword arguments so it's replayed as
+        # `rename_constraint(..., if_exists:)` rather than a positional hash
+        [:rename_constraint, [table_name, new_name, old_name, Hash.ruby2_keywords_hash(options)]]
+      end
+    end
+  end
+end

lib/active_record/pg_extensions/postgresql_adapter.rb

@@ -27,6 +27,17 @@ def defer_constraints(*constraints)
         set_constraints(:immediate, *constraints)
       end
 
+      # renames a constraint on a table
+      # see https://www.postgresql.org/docs/current/sql-altertable.html
+      def rename_constraint(table_name, old_name, new_name, if_exists: false)
+        return if if_exists && !constraint_exists?(table_name, name: old_name)
+
+        execute(<<~SQL.squish)
+          ALTER TABLE #{quote_table_name(table_name)}
+          RENAME CONSTRAINT #{quote_column_name(old_name)} TO #{quote_column_name(new_name)}
+        SQL
+      end
+
       # see https://www.postgresql.org/docs/current/sql-altertable.html#SQL-CREATETABLE-REPLICA-IDENTITY
       def set_replica_identity(table, identity = :default)
         identity_clause = case identity
@@ -285,6 +296,19 @@ def initialize_type_map(map = type_map)
         super
       end
 
+      def constraint_exists?(table_name, name:)
+        scope = quoted_scope(name)
+        table = quoted_scope(table_name)
+        select_value(<<~SQL, "SCHEMA") == 1
+          SELECT 1 FROM pg_constraint
+          INNER JOIN pg_class ON pg_class.oid = pg_constraint.conrelid
+          INNER JOIN pg_namespace ON pg_namespace.oid = pg_constraint.connamespace
+          WHERE pg_constraint.conname = #{scope[:name]}
+            AND pg_class.relname = #{table[:name]}
+            AND pg_namespace.nspname = #{scope[:schema]}
+        SQL
+      end
+
       def pre_pg10_wal_function_name(func)
         return func if postgresql_version >= 100_000
 

lib/active_record/pg_extensions/railtie.rb

@@ -10,9 +10,11 @@ class Railtie < Rails::Railtie
         ActiveSupport.on_load(:active_record) do
           require "active_record/pg_extensions/errors"
           require "active_record/pg_extensions/postgresql_adapter"
+          require "active_record/pg_extensions/command_recorder"
           require "active_record/pg_extensions/transaction"
 
           ::ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.prepend(PostgreSQLAdapter)
+          ::ActiveRecord::Migration::CommandRecorder.include(CommandRecorder)
           ::ActiveRecord::ConnectionAdapters::NullTransaction.prepend(NullTransaction)
           ::ActiveRecord::ConnectionAdapters::Transaction.prepend(Transaction)
           # if they've already require 'all', then inject now

lib/active_record/pg_extensions/version.rb

@@ -2,6 +2,6 @@
 
 module ActiveRecord
   module PGExtensions
-    VERSION = "0.7.0"
+    VERSION = "0.7.1"
   end
 end

spec/postgresql_adapter_spec.rb

@@ -436,4 +436,43 @@
       )
     end
   end
+
+  describe "#rename_constraint" do
+    around do |example|
+      connection.dont_execute(&example)
+    end
+
+    it "renames the constraint" do
+      connection.rename_constraint(:users, :old_chk, :new_chk)
+      expect(connection.executed_statements).to eq(
+        ['ALTER TABLE "users" RENAME CONSTRAINT "old_chk" TO "new_chk"']
+      )
+    end
+
+    context "with if_exists" do
+      it "skips when the constraint does not exist" do
+        allow(connection).to receive(:constraint_exists?).and_return(false)
+        connection.rename_constraint(:users, :old_chk, :new_chk, if_exists: true)
+        expect(connection.executed_statements).to be_empty
+      end
+
+      it "renames when the constraint exists" do
+        allow(connection).to receive(:constraint_exists?).and_return(true)
+        connection.rename_constraint(:users, :old_chk, :new_chk, if_exists: true)
+        expect(connection.executed_statements).to eq(
+          ['ALTER TABLE "users" RENAME CONSTRAINT "old_chk" TO "new_chk"']
+        )
+      end
+    end
+
+    it "is reversible" do
+      recorder = ActiveRecord::Migration::CommandRecorder.new(connection)
+      recorder.revert do
+        recorder.rename_constraint(:users, :old_chk, :new_chk, if_exists: true)
+      end
+      expect(recorder.commands).to eq(
+        [[:rename_constraint, [:users, :new_chk, :old_chk, { if_exists: true }]]]
+      )
+    end
+  end
 end