up

Documentation

Overview

Package up provides the common aspects among all upwards database schema migrators. This package may be imported by its sub-packages in order to provide the Migrator[S, U] generic interface for them.

Index

• type Migrator

Types

type Migrator

type Migrator[S any, U any] interface {
	// Settler returns a settler object (with S type) without performing
	// any migration action (so, no error condition may arise). Returned
	// settler object may be employed to persist the migration results.
	Settler() S

	// MigrateUp migrates from current major version to the next major
	// version by creating relevant views in a schema such as migN
	// based on the views in a schema such as migM where N=M+1
	// considering the latest supported minor versions of those N and M
	// major versions. It may be necessary to create tables and
	// materialize data items or load them in the Golang process memory
	// in more complex scenarios, but using views is preferred as it
	// postpones the actual data copying till the last schema and
	// the settlement phase.
	// It then creates another upwards migrator object (with U type)
	// which can be used for continuing the upwards migration from
	// the next major version similarly.
	MigrateUp(ctx context.Context) (U, error)
}

Migrator of S and U is a generic interface which presents expectations from a version-dependent database schema upwards migrator object. Each upwards migrator needs a MigrateUp method which is responsible to migrate one major version upwards (staying at the latest supported minor version). The U type parameter indicates the next upwards migrator type and S type parameter indicates the settler object type. After reaching to the target major version, Settler method can be used to obtain the corresponding settler object with type S and persist the migration results.

This generic interface must be implemented by all upmigN.Migrator types. It is useful for causing compile-time errors and catching programming errors when an old upmigN package is copied, but its methods are not updated properly in order to reflect the new version.