# `HephaestusEcto.Migration`
[🔗](https://github.com/lucas-stellet/hephaestus_ecto/blob/v0.3.0/lib/hephaestus_ecto/migration.ex#L1)

Migrations create and modify the database tables HephaestusEcto needs to function.

The migration API is versioned. `up/1` and `down/1` delegate to
`HephaestusEcto.Migrations.Postgres`, which applies incremental migration modules
(`V01`, `V02`, and so on) and records the applied schema version in the
`workflow_instances` table comment.

## Usage

To use migrations in your application you'll need to generate an `Ecto.Migration` that wraps
calls to `HephaestusEcto.Migration`:

    mix hephaestus_ecto.gen.migration

Or manually create a migration:

    defmodule MyApp.Repo.Migrations.AddHephaestus do
      use Ecto.Migration

      def up, do: HephaestusEcto.Migration.up()
      def down, do: HephaestusEcto.Migration.down()
    end

This original zero-argument API is still supported and migrates to the latest available
version.

## Isolation with Prefixes

HephaestusEcto supports namespacing through PostgreSQL schemas (prefixes):

    def up, do: HephaestusEcto.Migration.up(prefix: "private")
    def down, do: HephaestusEcto.Migration.down(prefix: "private")

## Versioning

Migrations are versioned and tracked via PostgreSQL table comments. Running `up/1`
only applies versions that haven't been run yet.

To upgrade incrementally to a specific version:

    def up, do: HephaestusEcto.Migration.up(version: 2)

To migrate down to a specific version:

    def down, do: HephaestusEcto.Migration.down(version: 1)

To inspect the currently applied version:

    HephaestusEcto.Migration.migrated_version()

# `down`

Run the `down` changes from the current version to the target version.

## Options

  * `:version` — target version to migrate down to (defaults to initial version)
  * `:prefix` — PostgreSQL schema prefix (defaults to `"public"`)

# `migrated_version`

Check the latest version the database is migrated to.

Returns `0` when the `workflow_instances` table hasn't been created yet.

## Options

  * `:prefix` — PostgreSQL schema prefix (defaults to `"public"`)

# `up`

Run the `up` changes for all migrations between the initial version and the current version.

The default call `up()` keeps the pre-0.2.0 API intact by migrating to the latest version.

## Options

  * `:version` — target version (defaults to latest)
  * `:prefix` — PostgreSQL schema prefix (defaults to `"public"`)

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*Consult [api-reference.md](api-reference.md) for complete listing*