DDL Postgres Macros

Wed, 29 Jan 2025 00:00:00 GMT

In postgres you may find yourself repeating common operations on all your tables. For example adding an audit log, created times, modified user etc.

This can be tedious to add everywhere. Instead, you can create a postgres “macro” to update your DDL for you

Example

Created

CREATE OR REPLACE FUNCTION public.add_created_columns(
    table_type regclass
) RETURNS void
    LANGUAGE plpgsql
    SET search_path TO ''
AS $_$
declare
    statement text = format($$
        alter table %1$s
            add column created_user int references public."user"(id) not null,
            add column created_at   timestamptz not null default current_timestamp;
        $$,
        $1);
begin
    execute statement;
end;
$_$;

Usage

To use the add_created_columns macro, you simply call it by passing the table name as a parameter. Here’s an example of how to use it:

SELECT public.add_created_columns('public.orders'),
       public.add_created_columns('public.products');

This will modify the specified table by adding the created_user and created_at columns as defined in the macro.

Modified

To add similar columns for tracking modifications, you can create a new macro called add_modified_columns. Here’s an example:

Note: this also adds a trigger to keep the modified at up to date.

   create or replace function update_modified_at()
    returns trigger as $$
begin
    new.modified_at = current_timestamp;
    return new;
end;
$$ language plpgsql;


CREATE OR REPLACE FUNCTION public.add_modified_columns(
table_type regclass
) RETURNS void
LANGUAGE plpgsql
SET search_path TO ''
AS $_$
declare
statement text = format($$
        alter table %1$s
            add column modified_user int references public."user"(id) not null,
            add column modified_at timestamptz not null default current_timestamp;

        create trigger update_modified_at_trigger
            before update on %1$s
            for each row
            execute function update_modified_at();
        $$,
        $1);

begin
execute statement;
end;
$_$;

Usage

To use the add_modified_columns macro, you can call it similarly as follows:

SELECT public.add_modified_columns('public.orders'),
       public.add_modified_columns('public.products');

This will modify the specified table by adding the modified_user and modified_at columns.

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Alias plpgsql variables

Thu, 24 Nov 2022 00:00:00 GMT

Inside plpgsql function you can often get naming conflicts between input parameters and column / table names

My previous modus operandi was to qualify the input param using the function name. For example:

Schema

create table data.user (
  id serial primary key;
  name text not null;
  birth_date date not null;
);

Options

Qualify using function name

create function age( "user" int ) returns int as
$$
  declare
    user_id alias for "user";
    --  user_id alias for $1; -- alternative
  begin
    select age(current_date, birth_date) from data.user where id = age.user ;
  end;
$$ language plpgsql;

ALIAS

But you can also use ALIAS FOR:

create function age( "user" int ) returns int as
$$
  declare
    user_id alias for "user";
    --  user_id alias for $1; -- alternative
  begin
    select age(current_date, birth_date) from data.user where id = user_id ;
  end;
$$ language plpgsql;

Aside: For a function that only does a single select a SQL language function is more appropriate.

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DDL Postgres Macros

Example

Created

Usage

Modified

Usage

Alias plpgsql variables

Schema

Options

Qualify using function name

ALIAS