migrate

Migrate is an exceedingly simple Postgres database migration tool.

The simplicity is manifested in the following principles:

• There are no "down" migrations. Because migrations necessarily mutate state on a live server, you can't have a safe rollback button.
• Migrations are not automatically executed within a transaction. Transactions are expensive, often unnecessary, and prevent certain operations (e.g. create index concurrently). If the migration warrants transactional semantics, simply include begin; ... ; commit; within the source of your migration.
• Migrations are not skipped if they are added out of order with regard to their version number, unlike some alternative tools. This handles the case where a migration is added in a feature branch, and no longer has the highest version number when merged into master.

Install

$ go get -u github.com/johngibb/migrate/cmd/migrate

This will install migrate to your $GOPATH/bin directory.

Usage

Create a migration:

$ migrate create -src <folder> <migration name>:
    Creates a new migration file.
  -src string
      directory containing migration files (default ".")

View pending and applied migrations:

$ migrate status:
    Display a list of pending and applied migrations.
  -conn string
      postgres connection string
  -src string
      directory containing migration files (default ".")

Apply pending migrations:

$ migrate up -src <migrations folder> -conn <connection string> [-quiet]:
    Apply all pending migrations.
  -conn string
      postgres connection string
  -quiet
      only print errors
  -src string
      directory containing migration files (default ".")

Migrations

Migrations are written as plain SQL scripts. All statements should be terminated with a semicolon, as migrate will execute the script one statement at a time.

A simple migration to add a users table might look like:

create table users (id int, name text);

A more complicated migration that uses a transaction to create multiple tables and build an index might look like:

begin;
create table users (id int, name text);
create table groups (id int, name text);
create table users_groups (user_id int, group_id int);
commit;
create index concurrently on users (id);

Development

To run the full integration tests, you'll need to have Docker for Mac installed.

make install  // compiles the entire project
make test     // runs the unit tests on your host machine
make test-all // compiles and runs all tests (including integration
              // tests against a Postgres instance) using Docker