Hasql.Queue.Migrate

Functions for migrating the database to create the necessary functions for the package.

Users can use these functions or copy and paste the tables to create these tables through a standalone migration system.

Documentation

migrationQueryString

Arguments

:: String

value column type, e.g. int4 or jsonb.

-> String

The DDL statements to create the schema given a value type.

migrate

Arguments

:: Connection

-> String

The type of the value column

-> IO ()

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

DO $$
 CREATE OR REPLACE FUNCTION notify_on(channel text) RETURNs VOID AS $$
   BEGIN
     EXECUTE (format(E'NOTIFY %I', channel));
   END;
 $$ LANGUAGE plpgsql;

 CREATE OR REPLACE FUNCTION listen_on(channel text) RETURNS VOID AS $$
   BEGIN
     EXECUTE (format(E'LISTEN %I', channel));
   END;
 $$ LANGUAGE plpgsql;

 CREATE OR REPLACE FUNCTION unlisten_on(channel text) RETURNS VOID AS $$
   BEGIN
     EXECUTE (format(E'UNLISTEN %I', channel));
   END;
 $$ LANGUAGE plpgsql;

   DO $$
 BEGIN
   IF NOT EXISTS (SELECT 1 FROM pg_type WHERE typname = state_t) THEN
     CREATE TYPE state_t AS ENUM (enqueued, failed);
   END IF;
 END$$;

 CREATE SEQUENCE IF NOT EXISTS modified_index START 1;

 CREATE TABLE IF NOT EXISTS payloads
 ( id BIGSERIAL PRIMARY KEY
 , attempts int NOT NULL DEFAULT 0
 , state state_t NOT NULL DEFAULT enqueued
 , modified_at int8 NOT NULL DEFAULT nextval(modified_index)
 , value ${VALUE_TYPE} NOT NULL
 );

 CREATE INDEX IF NOT EXISTS active_modified_at_idx ON payloads USING btree (modified_at, state)
   WHERE (state = enqueued);

The VALUE_TYPE needs to passed in through the second argument.

teardown :: Connection -> IO ()

Drop everything created by migrate