Auditing Data Changes with Triggers

-- Create an audit-specific schema and revoke all non-superuser privileges
DROP SCHEMA IF EXISTS audit CASCADE;
CREATE SCHEMA IF NOT EXISTS audit;
REVOKE CREATE ON SCHEMA audit FROM PUBLIC;

-- Audit table
CREATE TABLE audit.action_log (
  schema_name   TEXT                     NOT NULL,
  table_name    TEXT                     NOT NULL,
  user_name     TEXT,
  time          TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT CURRENT_TIMESTAMP,
  action        TEXT                     NOT NULL CHECK (action IN ('I', 'D', 'U')),
  original_data TEXT,
  new_data      TEXT,
  query         TEXT
) WITH (FILLFACTOR = 100
);

-- Audit table permissions
REVOKE ALL ON audit.action_log FROM PUBLIC;
GRANT SELECT ON audit.action_log TO PUBLIC;


-- Indexes
CREATE INDEX logged_actions_schema_table_idx
  ON audit.action_log (((schema_name || '.' || table_name) :: TEXT));

CREATE INDEX logged_actions_time_idx
  ON audit.action_log (time);

CREATE INDEX logged_actions_action_idx
  ON audit.action_log (action);
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-- Create audit trigger function
---------------------------------------------------------------
CREATE OR REPLACE FUNCTION audit.logger()
  RETURNS TRIGGER AS $body$
DECLARE
  v_old_data TEXT;
  v_new_data TEXT;
BEGIN
  IF (TG_OP = 'UPDATE')
  THEN
    v_old_data := ROW (OLD.*);
    v_new_data := ROW (NEW.*);
    INSERT INTO audit.action_log (schema_name, table_name, user_name, action, original_data, new_data, query)
    VALUES (TG_TABLE_SCHEMA :: TEXT, TG_TABLE_NAME :: TEXT, session_user :: TEXT, substring(TG_OP, 1, 1), v_old_data,
            v_new_data, current_query());
    RETURN NEW;
  ELSIF (TG_OP = 'DELETE')
    THEN
      v_old_data := ROW (OLD.*);
      INSERT INTO audit.action_log (schema_name, table_name, user_name, action, original_data, query)
      VALUES (TG_TABLE_SCHEMA :: TEXT, TG_TABLE_NAME :: TEXT, session_user :: TEXT, substring(TG_OP, 1, 1), v_old_data,
              current_query());
      RETURN OLD;
  ELSIF (TG_OP = 'INSERT')
    THEN
      v_new_data := ROW (NEW.*);
      INSERT INTO audit.action_log (schema_name, table_name, user_name, action, new_data, query)
      VALUES (TG_TABLE_SCHEMA :: TEXT, TG_TABLE_NAME :: TEXT, session_user :: TEXT, substring(TG_OP, 1, 1), v_new_data,
              current_query());
      RETURN NEW;
  ELSE
    RAISE WARNING '[AUDIT.IF_MODIFIED_FUNC] - Other action occurred: %, at %', TG_OP, now();
    RETURN NULL;
  END IF;

  EXCEPTION
  WHEN data_exception
    THEN
      RAISE WARNING '[AUDIT.IF_MODIFIED_FUNC] - UDF ERROR [DATA EXCEPTION] - SQLSTATE: %, SQLERRM: %', SQLSTATE, SQLERRM;
      RETURN NULL;
  WHEN unique_violation
    THEN
      RAISE WARNING '[AUDIT.IF_MODIFIED_FUNC] - UDF ERROR [UNIQUE] - SQLSTATE: %, SQLERRM: %', SQLSTATE, SQLERRM;
      RETURN NULL;
  WHEN OTHERS
    THEN
      RAISE WARNING '[AUDIT.IF_MODIFIED_FUNC] - UDF ERROR [OTHER] - SQLSTATE: %, SQLERRM: %', SQLSTATE, SQLERRM;
      RETURN NULL;
END;
$body$
LANGUAGE plpgsql
SECURITY DEFINER
SET search_path = pg_catalog, audit;

COMMENT ON FUNCTION audit.logger() IS 'Records insert, update, delete operations on specific tables';
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---------------------------------------------------------------
-- Last modification time audit trigger function
---------------------------------------------------------------
-- Records modification time before record changes
CREATE OR REPLACE FUNCTION audit.update_mtime()
  RETURNS TRIGGER AS $$
BEGIN
  NEW.mtime = now();
  RETURN NEW;
END;
$$ LANGUAGE 'plpgsql';

COMMENT ON FUNCTION audit.update_mtime() IS 'Updates record mtime';
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---------------------------------------------------------------
-- Metadata change event trigger function
-- Sends table name to 'change' channel for data changes
---------------------------------------------------------------
CREATE OR REPLACE FUNCTION audit.notify_change()
  RETURNS TRIGGER AS $$
BEGIN
  PERFORM pg_notify('change', TG_RELNAME);
  RETURN NULL;
END;
$$ LANGUAGE 'plpgsql';

COMMENT ON FUNCTION audit.notify_change() IS 'Data change event trigger function, sends table name to `change` channel for data changes';
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