Enum MigrationStep 

pub enum MigrationStep {
    Sql(Cow<'static, str>),
    Run(Box<dyn Fn(&Connection) -> Result<(), DbError> + Sync + Send>),
}

How a migration applies its change to the synced schema.

Variants

Sql(Cow<'static, str>)

A DDL batch (CREATE / ALTER / CREATE INDEX), e.g. include_str! of a .sql file.

Run(Box<dyn Fn(&Connection) -> Result<(), DbError> + Sync + Send>)

Table rebuilds and backfills that DDL alone cannot express. Invoked at most once (only when its version is above the on-disk one). All pending steps share the open transaction, so a failed step or routing validation rolls the full ladder back with user_version.