db/schema/0010_audit_and_soft_delete.sql

create type public.audit_kind as enum
  ( 'modify'
  , 'delete'
  , 'create'
  );

create type audited_column as (column_ text, type_ text);

create function audit(schema text, table_ text, tracked_columns audited_column[], soft_delete boolean)
  returns void
  language plpgsql as $$
  begin
    if soft_delete then
      perform setup_audit_and_soft_delete(schema, table_, tracked_columns);
    else
      perform setup_audit_and_hard_delete(schema, table_, tracked_columns);
    end if;
  end;
$$;

create function setup_audit_and_soft_delete( schema text
                                           , table_ text
                                           , tracked_columns audited_column[]
                                           )
  returns void
  language plpgsql as $$
  declare
    col audited_column;
    audit_table text := concat(schema, '.', table_, '_audit');
    do_table_audit text := concat(schema, '.do_', table_, '_audit');
    do_table_soft_delete text := concat(schema, '.do_', table_, '_soft_delete');
    create_audit_table text := '';
    create_do_table_audit text := '';
    create_do_table_soft_delete text := '';
    create_trigger_table_audit text := '';
    create_trigger_table_soft_delete text := '';
  begin
   -- create table X_audit() >>>
   create_audit_table := concat( create_audit_table
                               , 'create table ', audit_table, E'\n'
                               , '  ( ', table_, ' int not null references ', table_, '(id)', E'\n'
                               , '  , kind public.audit_kind not null', E'\n'
                               , '  , actor int not null references public.usr (id)', E'\n'
                               );

   foreach col in array tracked_columns loop
     create_audit_table := concat( create_audit_table
                                 , E'  , prev_', (col.column_), ' ', (col.type_), E' null\n'
                                 );
   end loop;

   create_audit_table := concat( create_audit_table
                               , '  );'
                               );
   -- <<< create table X_audit()

   -- create function do_X_soft_delete() >>>
   create_do_table_soft_delete := concat( create_do_table_soft_delete
                                  , 'create function ', do_table_soft_delete, E'() returns trigger language plpgsql as \$\$\n'
                                  , E'begin\n'
                                  , E'  insert into ', audit_table, E'\n'
                                  , E'    (', table_, E', kind, actor)\n'
                                  , E'  values\n'
                                  , E'    (OLD.id, \'delete\', (select (public.get_acting_usr()).id));\n'
                                  , E'\n'
                                  , E'  update ', schema, '.', table_, E'\n'
                                  , E'  set deleted = true\n'
                                  , E'  where id = OLD.id;\n'
                                  , E'\n'
                                  , E'  return null;\n'
                                  , E'end;\n'
                                  , E'\$\$;'
                                  );
   -- <<< create function do_X_soft_delete()

   -- create function do_X_audit() >>>
   create_do_table_audit := concat( create_do_table_audit
                                  , 'create function ', do_table_audit, E'() returns trigger language plpgsql as \$\$\n'
                                  , E'declare\n'
                                  , E'  audit_kind public.audit_kind;\n'
                                  , E'  id int;\n'
                                  );

   foreach col in array tracked_columns loop
     create_do_table_audit := concat( create_do_table_audit
                                    , 'prev_', (col.column_), ' ', (col.type_), E';\n'
                                    );
   end loop;

   create_do_table_audit := concat( create_do_table_audit
                                  , E'begin\n'
                                  , E'  if (TG_OP = \'INSERT\') then\n'
                                  , E'    id := NEW.id;\n'
                                  , E'    audit_kind := \'create\';\n'
                                  , E'  elsif (TG_OP = \'UPDATE\') then\n'
                                  , E'    id := OLD.id;\n'
                                  , E'    audit_kind := \'modify\';\n'
                                  );

   foreach col in array tracked_columns loop
     create_do_table_audit := concat( create_do_table_audit
                                    , '    prev_', (col.column_), ' := OLD.', (col.column_), E';\n'
                                    );
   end loop;

   create_do_table_audit := concat( create_do_table_audit
                                  , E'  end if;\n'
                                  , E'  insert into ', audit_table, E'\n'
                                  , '    (kind, ', table_, ', actor'
                                  );

   foreach col in array tracked_columns loop
     create_do_table_audit := concat( create_do_table_audit
                                    , ', prev_', (col.column_)
                                    );
   end loop;

   create_do_table_audit := concat( create_do_table_audit
                                  , E'  )\n'
                                  , E'  values\n'
                                  , E'    (audit_kind, id, (public.get_acting_usr()).id'
                                  );

   foreach col in array tracked_columns loop
     create_do_table_audit := concat( create_do_table_audit
                                    , ', prev_', (col.column_)
                                    );
   end loop;

   create_do_table_audit := concat( create_do_table_audit
                                  , E');\n'
                                  , E'  return NEW;\n'
                                  , E'end;\n'
                                  , E'\$\$;'
                                  );
   -- <<< create function do_X_audit()

   create_trigger_table_audit := concat( 'create trigger trigger_', table_, E'_audit\n'
                                       , 'after insert or update on ', schema, '.', table_, E'\n'
                                       , 'for each row execute function ', do_table_audit, '();'
                                       );
   create_trigger_table_soft_delete := concat( 'create trigger trigger_', table_, E'_soft_delete\n'
                                             , 'before delete on ', schema, '.', table_, E'\n'
                                             , 'for each row execute function ', do_table_soft_delete, '();'
                                             );
   execute create_audit_table;
   execute create_do_table_audit;
   execute create_do_table_soft_delete;
   execute create_trigger_table_audit;
   execute create_trigger_table_soft_delete;
  end;
$$;

create function setup_audit_and_hard_delete( schema text
                                           , table_ text
                                           , tracked_columns audited_column[]
                                           )
  returns void
  language plpgsql as $$
  declare
    col audited_column;
    audit_table text := concat(schema, '.', table_, '_audit');
    do_table_audit text := concat(schema, '.do_', table_, '_audit');
    do_table_soft_delete text := concat(schema, '.do_', table_, '_soft_delete');
    create_audit_table text := '';
    create_do_table_audit text := '';
    create_do_table_soft_delete text := '';
    create_trigger_table_audit text := '';
    create_trigger_table_soft_delete text := '';
  begin
   -- create table X_audit() >>>
   create_audit_table := concat( create_audit_table
                               , 'create table ', audit_table, E'\n'
                               , '  ( ', table_, ' int not null references ', table_, '(id)', E'\n'
                               , '  , kind public.audit_kind not null', E'\n'
                               , '  , actor int not null references public.usr (id)', E'\n'
                               );

   foreach col in array tracked_columns loop
     create_audit_table := concat( create_audit_table
                                 , E'  , prev_', (col.column_), ' ', (col.type_), E' null\n'
                                 );
   end loop;

   create_audit_table := concat( create_audit_table
                               , '  );'
                               );
   -- <<< create table X_audit()

   -- create function do_X_audit() >>>
   create_do_table_audit := concat( create_do_table_audit
                                  , 'create function ', do_table_audit, E'() returns trigger language plpgsql as \$\$\n'
                                  , E'declare\n'
                                  , E'  audit_kind public.audit_kind;\n'
                                  , E'  id int;\n'
                                  );

   foreach col in array tracked_columns loop
     create_do_table_audit := concat( create_do_table_audit
                                    , 'prev_', (col.column_), ' ', (col.type_), E';\n'
                                    );
   end loop;

   create_do_table_audit := concat( create_do_table_audit
                                  , E'begin\n'
                                  , E'  if (TG_OP = \'INSERT\') then\n'
                                  , E'    id := NEW.id;\n'
                                  , E'    audit_kind := \'create\';\n'
                                  , E'  elsif (TG_OP = \'DELETE\') then\n'
                                  , E'    id := OLD.id;\n'
                                  , E'    audit_kind := \'delete\';\n'
                                  , E'  elsif (TG_OP = \'UPDATE\') then\n'
                                  , E'    id := OLD.id;\n'
                                  , E'    audit_kind := \'modify\';\n'
                                  );

   foreach col in array tracked_columns loop
     create_do_table_audit := concat( create_do_table_audit
                                    , '    prev_', (col.column_), ' := OLD.', (col.column_), E';\n'
                                    );
   end loop;

   create_do_table_audit := concat( create_do_table_audit
                                  , E'  end if;\n'
                                  , E'  insert into ', audit_table, E'\n'
                                  , '    (kind, ', table_, ', actor'
                                  );

   foreach col in array tracked_columns loop
     create_do_table_audit := concat( create_do_table_audit
                                    , ', prev_', (col.column_)
                                    );
   end loop;

   create_do_table_audit := concat( create_do_table_audit
                                  , E'  )\n'
                                  , E'  values\n'
                                  , E'    (audit_kind, id, (public.get_acting_usr()).id'
                                  );

   foreach col in array tracked_columns loop
     create_do_table_audit := concat( create_do_table_audit
                                    , ', prev_', (col.column_)
                                    );
   end loop;

   create_do_table_audit := concat( create_do_table_audit
                                  , E');\n'
                                  , E'  return NEW;\n'
                                  , E'end;\n'
                                  , E'\$\$;'
                                  );
   -- <<< create function do_X_audit()

   create_trigger_table_audit := concat( 'create trigger trigger_', table_, E'_audit\n'
                                       , 'after insert or update or delete on ', schema, '.', table_, E'\n'
                                       , 'for each row execute function ', do_table_audit, '();'
                                       );
   execute create_audit_table;
   execute create_do_table_audit;
   execute create_do_table_soft_delete;
   execute create_trigger_table_audit;
   execute create_trigger_table_soft_delete;
  end;
$$;