ralli / dbmigrate

experiment to implement database migrations

Database Migrations

This project implements an experimental database migration tool. Experimental means it is work in progress and not useful for any particular use case other than playing around.

It implements two different types of migrations:

1. classical migrations, known from tools like liquibase and flyway
2. script migrations for database objects like views and stored procedures which may be executed multiple times but only if the view / procedure actually changed.

Classical migrations

Classical migrations work like expected. Migrations are written in SQL-Format and are executed in sorted order. 202206061113_create_table_person.sql will be executed before 202206061115_create_table_address.sql.

An example migration:

create table person
(
    person_id  int,
    first_name varchar(40),
    last_name  varchar(40)
);

create index ix_person_1 on person(person_id);

-- optional rollback statement 
-- rollback: drop table person;

Script migrations

Some database changes made do not need to be executed once only. If views and stored procedures are changed, they may be recreated without deleting existing data - as in the case of database tables.

• Develop like in classical software projects: Views and stored procedures are developed like classical software. Stored procedures and views will be developed in classical database tools.
• Only modified artifacts will be deployed: When it comes to packaging, only artifacts which have been modified will be deployed to the database.
• The deployment script will keep track of all script changes deployed to the database.

Dependency graph

Dependencies in scripts are currently managed by annotation comments.

The following example shows a view with dependency on views declared in files named stg__person.sql and stg__email.sql. The migrations will be executed in topological order. stg__person.sql and stg__email.sql will be executed before person_details.sql.

-- 
-- depends: stg__person, stg__email
--
create or replace view person_details as
(
    select stg__person.id,
           stg__person.first_name,
           stg__person.last_name,
           stg__email.email
    from stg__person
             join stg__email on stg__email.person_id = stg__person.person_id
)