Struct ConstraintMap 

pub struct ConstraintMap { /* private fields */ }

Consumer-registered map from DB UNIQUE-constraint violations to field-level validation errors. Construct per call site (cheap; no global state).

First-match semantics

Entries are matched in registration order. The first entry whose Postgres constraint name or SQLite table.column key matches the violation wins. Register the most specific entries first when multiple UNIQUE constraints exist on one table.

Postgres vs SQLite identity

• Postgres: matched by constraint name via the DatabaseError::constraint() trait method (protocol field 'n'). No message-string parsing.
• SQLite: matched by table.column extracted from the error message ("UNIQUE constraint failed: table.column"). SQLite does not expose structured constraint names so the message token is the reliable identifier.

A single registration can cover both backends by chaining .sqlite("t.c") after .on(...).

Implementations

impl ConstraintMap

pub fn new() -> Self

Create an empty ConstraintMap.

pub fn on( self, pg_constraint: impl Into<String>, field: impl Into<String>, message: impl Into<String>, ) -> Self

Register a UNIQUE constraint name → field/message mapping.

pg_constraint is the Postgres constraint name (the structured value in the DB error protocol, e.g. "pages_slug_unique"). It is also used as the logical entry key when chaining .sqlite(...).

Optionally chain .sqlite("table.column") immediately after to add a SQLite discriminator to the same entry so one registration covers both backends.

Example

ConstraintMap::new()
    .on("pages_slug_unique", "slug", "has already been taken")
    .sqlite("pages.slug");

pub fn sqlite(self, table_col: impl Into<String>) -> Self

Add a SQLite table.column discriminator to the LAST registered entry.

Must be chained immediately after .on(...). No-op when called without a prior .on() call on this map.

SQLite does not expose structured constraint names; the table.column token parsed from the error message is the reliable identifier for SQLite backends (dev/CI environments).

pub fn try_map(&self, err: DbErr) -> Result<ValidationError, DbErr>

Map a DB UNIQUE-constraint violation to a field-level ValidationError.

Returns Ok(ValidationError) when err is a UNIQUE violation that matches a registered entry. Returns Err(err) unchanged (by move) when:

• err is not a UNIQUE violation, or
• err is a UNIQUE violation but no registered entry matches.

The returned ValidationError carries the entry’s field and message and composes with .with_old_input(&data).into_action_error(url) exactly like a Phase 190 async-rule failure.

Safety contract (SC2)

This method NEVER swallows a DbErr. A non-matching error is returned unchanged so the caller’s ? reaches From<DbErr> for ActionError.

Trait Implementations

impl Clone for ConstraintMap

fn clone(&self) -> ConstraintMap

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Default for ConstraintMap

fn default() -> ConstraintMap

Returns the “default value” for a type.