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