FIX: `TableMigrationHelper` didn't clean up after itself.

lib/table_migration_helper.rb

@@ -1,7 +1,7 @@
 class TableMigrationHelper
   def self.read_only_table(table_name)
     ActiveRecord::Base.exec_sql <<-SQL
-    CREATE OR REPLACE FUNCTION raise_read_only() RETURNS trigger AS $rro$
+    CREATE OR REPLACE FUNCTION #{readonly_function_name(table_name)} RETURNS trigger AS $rro$
       BEGIN
         RAISE EXCEPTION 'Discourse: Table is read only';
         RETURN null;
@@ -10,22 +10,21 @@ class TableMigrationHelper
     SQL
 
     ActiveRecord::Base.exec_sql <<-SQL
-    CREATE TRIGGER #{table_name}_read_only
+    CREATE TRIGGER #{readonly_trigger_name(table_name)}
     BEFORE INSERT OR UPDATE OR DELETE OR TRUNCATE
     ON #{table_name}
     FOR EACH STATEMENT
-    EXECUTE PROCEDURE raise_read_only();
+    EXECUTE PROCEDURE #{readonly_function_name(table_name)};
     SQL
   end
 
   def self.delayed_drop(old_name:, new_name:, after_migration:, delay: nil, on_drop: nil)
-    delay ||= Rails.env.production? ? 300 : 0
+    delay ||= Rails.env.production? ? 3600 : 0
 
-   sql = <<SQL
+   sql = <<~SQL
     SELECT 1
     FROM INFORMATION_SCHEMA.TABLES
     WHERE table_schema = 'public' AND
-          table_name = :old_name AND
           EXISTS (
             SELECT 1
             FROM schema_migration_details
@@ -39,15 +38,30 @@ class TableMigrationHelper
             table_name = :new_name
           )
     LIMIT 1
-SQL
+    SQL
 
     if ActiveRecord::Base.exec_sql(sql, old_name: old_name,
                                         new_name: new_name,
                                         delay: "#{delay.to_i || 0} seconds",
                                         after_migration: after_migration).to_a.length > 0
-      on_drop&.call
 
-        ActiveRecord::Base.exec_sql("DROP TABLE #{old_name}")
+      on_drop&.call
+      ActiveRecord::Base.exec_sql("DROP TABLE IF EXISTS #{old_name}")
+
+      ActiveRecord::Base.exec_sql <<~SQL
+      DROP TRIGGER IF EXISTS #{readonly_trigger_name(old_name)} ON #{old_name};
+      DROP FUNCTION IF EXISTS #{readonly_function_name(old_name)} CASCADE;
+      SQL
     end
   end
+
+  private
+
+    def self.readonly_function_name(table_name)
+      "public.raise_#{table_name}_read_only()"
+    end
+
+    def self.readonly_trigger_name(table_name)
+      "#{table_name}_read_only"
+    end
 end