Database.Schema.Migrations.Store

This module provides an abstraction for a migration store, a facility in which Migrations can be stored and from which they can be loaded. This module also provides functions for taking Migrations from a store and converting them into the appropriate intermediate types for use with the rest of this library.

Documentation

data MigrationStore

The type of migration storage facilities. A MigrationStore is a facility in which new migrations can be created, and from which existing migrations can be loaded.

Constructors

MigrationStore

Fields

loadMigration :: String -> IO (Either String Migration)

Load a migration from the store.

saveMigration :: Migration -> IO ()

Save a migration to the store.

getMigrations :: IO [String]

Return a list of all available migrations' names.

fullMigrationName :: String -> IO String

Return the full representation of a given migration name; mostly for filesystem stores, where the full representation includes the store path.

data MapValidationError

A type for types of validation errors for migration maps.

Constructors

DependencyReferenceError String String

A migration claims a dependency on a migration that does not exist.

DependencyGraphError String

An error was encountered when constructing the dependency graph for this store.

InvalidMigration String

The specified migration is invalid.

Instances

Eq MapValidationError

Show MapValidationError

data StoreData

Constructors

StoreData

Fields

storeDataMapping :: MigrationMap

storeDataGraph :: DependencyGraph Migration

type MigrationMap = Map String Migration

A mapping from migration name to Migration. This is exported for testing purposes, but you'll want to interface with this through the encapsulating StoreData type.

High-level Store API

loadMigrations :: MigrationStore -> IO (Either [MapValidationError] StoreData)

Load migrations from the specified MigrationStore, validate the loaded migrations, and return errors or a MigrationMap on success. Generally speaking, this will be the first thing you should call once you have constructed a MigrationStore.

storeMigrations :: StoreData -> [Migration]

A convenience function for extracting the list of Migrations extant in the specified StoreData.

storeLookup :: StoreData -> String -> Maybe Migration

A convenience function for looking up a Migration by name in the specified StoreData.

Miscellaneous Functions

depGraphFromMapping :: MigrationMap -> Either String (DependencyGraph Migration)

Create a DependencyGraph from a MigrationMap; returns Left if the dependency graph cannot be constructed (e.g., due to a dependency cycle) or Right on success. Generally speaking, you won't want to use this directly; use loadMigrations instead.

validateMigrationMap :: MigrationMap -> [MapValidationError]

Validate a migration map. Returns zero or more validation errors.

validateSingleMigration :: MigrationMap -> Migration -> [MapValidationError]

Validate a single migration. Looks up the migration's dependencies in the specified MigrationMap and returns a MapValidationError for each one that does not exist in the map.

leafMigrations :: StoreData -> [String]

Finds migrations that no other migration depends on (effectively finds all vertices with in-degree equal to zero).