# Database migration

[Detailed information about this](http://ian-shafer.github.io/2016/02/02/db-migrations/)

## Setup

#### Configuration
The credentials for each environment that could be updated is stored in the
`env/` directory.

***Example***

`env/default.conf` could look like this:
```
#!/bin/bash
export PSQL_OPTS="-h HOST_NAME -U USER_NAME"
export DB_NAME=DATABASE_NAME
```

Create one file for each environment you'd be able to migrate.

When `db-upgrade` is issued, it takes the first part of any name as argument and
performs the migration on selected environment.

`$ ./db-upgrade localhost` would for example find a file named `localhost.conf`
and use the credentials inside for the migration.

To avoid having to enter password for selected user on each run, just use a
[.pgpass](http://www.postgresql.org/docs/9.3/static/libpq-pgpass.html) file.

`db-upgrade` assumes the `default` environment should be used if it's argument
is omitted. So, start by creating an initial `default.conf` with credentials for your localhost or some non-critical environment.

#### Migration files
The files in the /migrations directory are changes to the scheme, not the full
scheme.

The naming convention for migration files are:
- 000.000.sql
- 000.001.sql
- 000.002.sql
- 000.003.sql
- 000.004.sql
- ...and so on

**Example**
The first file, `migrations/000.000.sql` may look like this:
```
create table users (
  name varchar(32) not null,
  primary key (name)
);
```

The second file, `migrations/000.001.sql` may look like this:
```
alter table users
add email varchar(256) not null;
```

To do the actual migration, then just run:
```
# ./db-upgrade [ENVIRONMENT NAME]
```

**Example docker-compose.yml for postgres**

Execute this first:
```bash
mkdir data
chmod o+rwx data
```

```yml
version: '3.7'

services:
  db:
    image: postgres:13
    restart: always
    environment:
      POSTGRES_PASSWORD: postgres
      TZ: 'Europe/Stockholm'
      PGTZ: 'Europe/Stockholm'
    ports:
      - "5432:5432"
    volumes:
      - ./data:/var/lib/postgresql/data
      - /var/run/postgresql:/var/run/postgresql

networks:
  default:
    external: true
    name: postgres
```