Database.PostgreSQL.Simple.Queue.Migrate

Documentation

migrate :: String -> Connection -> IO ()

This function creates a table and enumeration type that is appriopiate for the queue. The following sql is used.

CREATE TYPE state_t AS ENUM (enqueued, locked, dequeued);

CREATE TABLE payloads
( id uuid PRIMARY KEY
, value jsonb NOT NULL
, state state_t NOT NULL DEFAULT enqueued
, created_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT clock_timestamp()
, modified_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT clock_timestamp()
);

CREATE INDEX state_idx ON payloads (state);

CREATE OR REPLACE FUNCTION update_row_modified_function_()
RETURNS TRIGGER
AS
$$
BEGIN
    -- ASSUMES the table has a column named exactly "modified_at".
    -- Fetch date-time of actual current moment from clock,
    -- rather than start of statement or start of transaction.
    NEW.modified_at = clock_timestamp();
    RETURN NEW;
END;
$$
language plpgsql;