Enum NarrowingStrategy 

#[non_exhaustive]
pub enum NarrowingStrategy {
    Truncate,
    Delete,
    SetToValue {
        value: String,
    },
}

How an existing row that violates the new (narrowed) column type should be transformed before the ALTER COLUMN TYPE statement runs.

The wire format uses an internally tagged JSON representation ({"kind": "..."}) so future variants stay backwards compatible. The enum is #[non_exhaustive] — downstream match expressions must include a wildcard arm.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Truncate

Trim the violating value to fit the new type. The row is preserved; only the column value loses its overflowing tail.

Applicable to string-like narrowings (varchar(N), char(N), text -> varchar(N)) via LEFT(col, N) / substr(col, 1, N), and to NUMERIC scale narrowing via ROUND(col, new_scale).

Not applicable to integer / float / timezone narrowings — truncation has no natural definition there. The CLI revision UI hides this option for those cases.

Delete

Delete the entire row containing a violating value. Other columns of that row are lost along with it.

Universally applicable across every narrowing kind. Watch for FK cascade behaviour — deleting a parent row with ON DELETE CASCADE can propagate into child tables.

SetToValue

Replace the violating value with a fixed sentinel that fits the new type. The row is preserved; only the violating column is rewritten.

The value field is emitted verbatim into the generated SQL (UPDATE ... SET col = <value>), so callers must quote string literals themselves (e.g. "'TRUNCATED'", not "TRUNCATED") and must ensure the value itself fits the new type — otherwise the migration will fail in a different way.

Universally applicable across every narrowing kind, including integer overflow (e.g. value: "0") and timezone loss (e.g. value: "(now() AT TIME ZONE 'UTC')").

Fields

value: String

SQL fragment substituted for violating values. Strings must be pre-quoted by the caller. The CLI revision prompt wraps user input with single quotes automatically when the new type is a string-like type.

Implementations

impl NarrowingStrategy

pub fn kind_label(&self) -> &'static str

Tag name used in JSON wire format and CLI output (truncate, delete, set_to_value). #[non_exhaustive] is enforced at downstream-crate boundaries; this in-crate match is exhaustive.

Trait Implementations

impl Clone for NarrowingStrategy

fn clone(&self) -> NarrowingStrategy

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for NarrowingStrategy

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for NarrowingStrategy

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Eq for NarrowingStrategy

impl JsonSchema for NarrowingStrategy

fn schema_name() -> Cow<'static, str>

The name of the generated JSON Schema.

fn schema_id() -> Cow<'static, str>

Returns a string that uniquely identifies the schema produced by this type.

fn json_schema(generator: &mut SchemaGenerator) -> Schema

Generates a JSON Schema for this type.

fn inline_schema() -> bool

Whether JSON Schemas generated for this type should be included directly in parent schemas, rather than being re-used where possible using the $ref keyword.

impl PartialEq for NarrowingStrategy

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for NarrowingStrategy

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for NarrowingStrategy