Contributing Code
=================

## Database Modifications

### Adding/Updating tables

Database schemas are managed by a series of migrations defined in go code. We use a customized version of the Goose migrations tool to handle these migrations.

Note: Once committed to the Kolide repo, table migrations should be considered immutable. Any changes to an existing table should take place in a new migration executing ALTERs.

  * From the project root run the following shell commands:

  ``` bash
  go get github.com/kolide/goose
  cd server/datastore/mysql/migrations/tables
  goose create AddColumnFooToUsers
  ```

  * Find the file you created in the migrations directory and edit it

  ``` go
  package migration

  import (
  	"database/sql"

  	"github.com/kolide/goose"
  )

  func init() {
  	goose.AddMigration(Up_20161118212656, Down_20161118212656)
  }

  func Up_20161118212656(tx *sql.Tx) error {
  	_, err := tx.Exec("ALTER TABLE `users` ADD COLUMN `foo` varchar(10) NOT NULL;")
  	return err
  }

  func Down_20161118212656(tx *sql.Tx) error {
  	_, err := tx.Exec("ALTER TABLE `users` DROP COLUMN `foo`;")
  	return err
  }
  ```

  * Update the database by running the following shell commands:

  ``` bash
  make build
  build/kolide prepare db
  ```

### Populating the database with default data

Populating built in data is also performed through migrations. All table migrations are performed before any data migrations.

Note: Data migrations can be mutable. If tables are altered in a way that would render a data migration invalid (columns changed/removed), data migrations should be updated to comply with the new schema. Data migrations will not be re-run when they have already been run against a database, but they must be updated to maintain compatibility with a fresh DB.

  * From the project root run the following shell commands:

  ``` bash
  go get github.com/kolide/goose
  cd server/datastore/mysql/migrations/data
  goose create PopulateFoo
  ```

  * Proceed as for table migrations, editing and running the newly created migration file.