| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Database.Schema.Migrations.Backend
- class Monad m => Backend b m where
- getBootstrapMigration :: b -> m Migration
- isBootstrapped :: b -> m Bool
- applyMigration :: b -> Migration -> m ()
- revertMigration :: b -> Migration -> m ()
- getMigrations :: b -> m [String]
- rootMigrationName :: String
Documentation
class Monad m => Backend b m where Source
A Backend represents a database engine backend such as MySQL or SQLite. A Backend supplies relatively low-level functions for inspecting the backend's state, applying migrations, and reverting migrations. A Backend also supplies the migration necessary to "bootstrap" a backend so that it can track which migrations are installed.
Methods
getBootstrapMigration :: b -> m Migration Source
The migration necessary to bootstrap a database with this connection interface. This might differ slightly from one backend to another.
isBootstrapped :: b -> m Bool Source
Returns whether the backend has been bootstrapped. A backend has been bootstrapped if is capable of tracking which migrations have been installed; the "bootstrap migration" provided by getBootstrapMigration should suffice to bootstrap the backend.
applyMigration :: b -> Migration -> m () Source
Apply the specified migration on the backend. applyMigration does NOT assume control of the transaction, since it expects the transaction to (possibly) cover more than one applyMigration operation. The caller is expected to call commit at the appropriate time. If the application fails, the underlying SqlError is raised and a manual rollback may be necessary; for this, see withTransaction from HDBC.
revertMigration :: b -> Migration -> m () Source
Revert the specified migration from the backend and record this action in the table which tracks installed migrations. revertMigration does NOT assume control of the transaction, since it expects the transaction to (possibly) cover more than one revertMigration operation. The caller is expected to call commit at the appropriate time. If the revert fails, the underlying SqlError is raised and a manual rollback may be necessary; for this, see withTransaction from HDBC. If the specified migration does not supply a revert instruction, this has no effect other than bookkeeping.
getMigrations :: b -> m [String] Source
Returns a list of installed migration names from the backend.
Instances
| IConnection conn => Backend conn IO | General Backend instance for all IO-driven HDBC connection implementations. You can provide a connection-specific instance if need be; this implementation is provided with the hope that you won't have to do that. |
rootMigrationName :: String Source
Backend instances should use this as the name of the migration returned by getBootstrapMigration; this migration is special because it cannot be reverted.