improve function creation process

lib/iron_trail/db_functions.rb

@@ -36,14 +36,27 @@ def collect_tracked_table_names
       connection.execute(stmt).map { |row| row['table'] }
     end
 
-    def collect_all_tables(table_schema: 'public')
+    def function_present?(function: 'irontrail_log_row', schema: 'public')
+      stmt = <<~SQL
+        SELECT 1 FROM "pg_proc" p
+        INNER JOIN "pg_namespace" ns
+        ON (ns.oid = p.pronamespace)
+        WHERE p."proname"=#{connection.quote(function)}
+          AND ns."nspname"=#{connection.quote(schema)}
+        LIMIT 1;
+      SQL
+
+      connection.execute(stmt).to_a.count > 0
+    end
+
+    def collect_all_tables(schema: 'public')
       # query pg_class rather than information schema because this way
       # we can get only regular tables and ignore partitions.
       stmt = <<~SQL
         SELECT c.relname AS "table"
         FROM "pg_class" c INNER JOIN "pg_namespace" ns
         ON (ns.oid = c.relnamespace)
-        WHERE ns.nspname=#{connection.quote(table_schema)}
+        WHERE ns.nspname=#{connection.quote(schema)}
           AND c.relkind IN ('r', 'p')
           AND NOT c.relispartition
         ORDER BY "table" ASC;

lib/iron_trail/migration.rb

@@ -25,7 +25,12 @@ def method_missing(method, *args)
         return result
       end
 
-      IronTrail::DbFunctions.new(connection).enable_tracking_for_table(table_name)
+      db_fun = IronTrail::DbFunctions.new(connection)
+      if db_fun.function_present?
+        db_fun.enable_tracking_for_table(table_name)
+      else
+        Rails.logger.warn("IronTrail will not create trigger for table #{table_name} because the trigger function does not exist in the database.")
+      end
 
       result
     end

spec/dummy_app/db/migrate/20241112090542_setup_test_db.rb

@@ -2,8 +2,6 @@
 
 class SetupTestDb < ::ActiveRecord::Migration::Current
   def up
-    IronTrail::DbFunctions.new(connection).install_functions
-
     create_table :people, id: :bigserial, force: true do |t|
       t.string :first_name, null: false
       t.string :last_name, null: false