A Migration is a four level monad stack consisting of:

• WriterT [Text] representing a log of errors in the migrations.
• WriterT CautiousMigration representing a list of migrations to run, along with whether or not they are safe.
• ReaderT SqlBackend, aka the SqlPersistT transformer for database interop.
• IO for arbitrary IO.

A list of SQL operations, marked with a safety flag. If the Bool is True, then the operation is *unsafe* - it might be destructive, or otherwise not idempotent. If the Bool is False, then the operation is *safe*, and can be run repeatedly without issues.

Convert a Migration to a list of Text values corresponding to their Sql statements.

Given a Migration, this parses it and returns either a list of errors associated with the migration or a list of migrations to do.

Like parseMigration, but instead of returning the value in an Either value, it calls error on the error values.

Prints a migration.

Return all of the Sql values associated with the given migration. Calls error if there's a parse error on any migration.

Runs a migration. If the migration fails to parse or if any of the migrations are unsafe, then this throws a PersistUnsafeMigrationException.

Same as runMigration, but does not report the individual migrations on stderr. Instead it returns a list of the executed SQL commands.

This is a safer/more robust alternative to runMigrationSilent, but may be less silent for some persistent implementations, most notably persistent-postgresql

Since: 2.10.2

Same as runMigration, but returns a list of the SQL commands executed instead of printing them to stderr.

This function silences the migration by remapping stderr. As a result, it is not thread-safe and can clobber output from other parts of the program. This implementation method was chosen to also silence postgresql migration output on stderr, but is not recommended!

Like runMigration, but this will perform the unsafe database migrations instead of erroring out.

Same as runMigrationUnsafe, but returns a list of the SQL commands executed instead of printing them to stderr.

Since: 2.10.2

Given a list of old entity definitions and a new EntityDef in val, this creates a Migration to update the old list of definitions with the new one.

Report multiple errors in a Migration.

Since: 2.9.2

Report a single error in a Migration.

Since: 2.9.2

Add a CautiousMigration (aka a [(Bool, Text)]) to the migration plan.

Since: 2.9.2

Add a migration to the migration plan.

Since: 2.9.2

Run an action against the database during a migration. Can be useful for eg creating Postgres extensions:

runSqlCommand $ rawExecute "CREATE EXTENSION IF NOT EXISTS "uuid-ossp";" []

Since: 2.13.0.0

An exception indicating that Persistent refused to run some unsafe migrations. Contains a list of pairs where the Bool tracks whether the migration was unsafe (True means unsafe), and the Sql is the sql statement for the migration.

Since: 2.11.1.0