Enum Down 

pub enum Down {
    Statements(Vec<String>),
    Irreversible(String),
}

How a migration undoes itself.

An enum rather than a possibly-empty Vec, because “this cannot be undone” and “nobody wrote a down step” are different facts and only one of them is a bug. A rollback refuses on Irreversible and prints the reason, instead of doing nothing and reporting success.

Variants

Statements(Vec<String>)

The statements that undo this migration, in the order they should run.

Irreversible(String)

Deliberately not reversible, and why.

A migration that drops a column or rewrites data cannot restore what it destroyed. Saying so is more useful than a down that runs cleanly and leaves the database subtly wrong.

Implementations

impl Down

pub fn statements(statements: impl IntoIterator<Item = String>) -> Self

Undone by these statements.

pub fn irreversible(reason: impl Into<String>) -> Self

Not reversible, for the stated reason.

pub fn sql(&self, migration: &str) -> Result<&[String]>

The statements, or an error naming the migration and why it has none.

pub fn is_reversible(&self) -> bool

Whether this migration can be rolled back.

Trait Implementations

impl Clone for Down

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Down

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for Down

impl PartialEq for Down

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Down