Enum ConflictTarget 

#[non_exhaustive]
pub enum ConflictTarget {
    PrimaryKey,
    Columns(&'static [&'static str]),
    ColumnsWithPredicate(&'static [&'static str], &'static str),
    PrimaryKeyWithPredicate(&'static str),
}

Conflict target for an upsert. Defaults to the model’s primary key (matching the previous PK-only behavior). Self::Columns / Self::columns let callers upsert on an arbitrary unique tuple — most commonly a natural key that’s distinct from the PK (e.g. (owner_id, provider) on a per-owner-and-provider settings row, or (pairing_id, slot) on a per-slot envelope).

The named columns MUST correspond to a UNIQUE constraint or UNIQUE index on the target table — the database engine enforces this and will surface a clear error if not. The upsert builder additionally requires the input to carry a value for every column in the target tuple, so the conflict probe (SELECT … FOR UPDATE) has something to filter on. A column that IS present but whose value is one of the SqlValue::Null* variants satisfies this requirement — the probe then filters on column = NULL, which never matches any row (three-valued SQL logic), so an upsert keyed on a NULL natural-key column always takes the insert branch. That is deliberate, not merely convenient: it is the same rule a WHERE col IS NOT NULL partial index encodes, so a NULL key naturally falls outside such an index’s uniqueness domain both in Postgres’s own ON CONFLICT inference and in this crate’s conflict probe.

Composite-constraint-by-name (ON CONFLICT ON CONSTRAINT my_unique_idx_v2) is not yet exposed; pass the matching column tuple via Self::Columns instead.

Partial unique indexes (cratestack#741)

Self::where_index attaches an index predicate so an upsert can target a partial unique index (CREATE UNIQUE INDEX ... WHERE <predicate>) — Postgres will not infer a partial index from an unpredicated ON CONFLICT (<cols>), so without this the statement fails at runtime with “there is no unique or exclusion constraint matching the ON CONFLICT specification”. The predicate is kept a &'static str, exactly like the column names: a compile-time constant from the schema/call site, passed through to the database verbatim, with no runtime-value path into the rendered SQL (the same precedent @@index’s using/opclass already set).

The predicate is not just appended to the emitted ON CONFLICT (…) WHERE … clause — every conflict probe this crate’s runtimes issue to decide Inserted vs. Existing/DO UPDATE also applies it. Skipping that half would let the probe match a row the partial index does not cover, handing the caller a wrong verdict even though the emitted SQL looks correct.

Declaring a partial index in the schema DDL (@@unique([...], where: "...")) is a separate concern (cratestack#742): this type only lets an upsert target a partial index that already exists.

Why an enum with four variants, not two plus a predicate field

An earlier draft of this ticket’s fix collapsed this type into a { kind, predicate } struct, which deleted the public PrimaryKey and Columns(&'static [&'static str]) variants direct construction / pattern-matching relied on. A repo-wide grep showed every in-repo call site only ever constructs a ConflictTarget (never pattern- matches one), so that break bought nothing — the maintainer ruled this be reworked additively instead (cratestack#741 finding 3): Self::PrimaryKey and Self::Columns are restored exactly as they were pre-#741, and the predicate rides along on two new, purely additive variants (Self::ColumnsWithPredicate, Self::PrimaryKeyWithPredicate) reached through Self::where_index rather than constructed directly. The invalid PrimaryKey + predicate combination deliberately stays representable (via Self::PrimaryKeyWithPredicate) rather than being ruled out at the type level, so Self::validate can reject it at runtime with a clear CratestackError::Validation instead of the type system silently preventing the chain PrimaryKey.where_index(..) from being written at all.

#[non_exhaustive] (cratestack#741 finding 4 follow-up, maintainer-ruled)

This release already breaks any external crate that pattern-matches ConflictTarget exhaustively without a wildcard arm — the variant count just grew from two to four (see above), and that alone forces such a match to stop compiling. #[non_exhaustive] costs nothing additional on top of a break those callers must already absorb this release, and it means every future variant addition is non-breaking for anyone who updates their match now — deferring it would mean paying a second, separate break later for no extra benefit, so this is the cheapest moment it will ever be. It affects matching only: every existing variant, including the two additive predicate-carrying ones, stays constructible from outside this crate exactly as before — #[non_exhaustive] on an enum blocks exhaustive matches and enum-level struct-update syntax in other crates, not construction of variants that already exist. (Putting #[non_exhaustive] on an individual variant instead would be the opposite mistake — that blocks construction — and is deliberately not done here.)

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.

PrimaryKey

The model’s @id primary key, unpredicated. Default.

Columns(&'static [&'static str])

A caller-supplied tuple of columns forming a unique key on the target table, unpredicated. Chain Self::where_index to target a partial unique index instead of a plain one.

ColumnsWithPredicate(&'static [&'static str], &'static str)

Additive (cratestack#741): Self::Columns with an attached partial-unique-index predicate. Reached via ConflictTarget::columns(&[...]).where_index(<predicate>); not normally constructed directly.

PrimaryKeyWithPredicate(&'static str)

Additive (cratestack#741): Self::PrimaryKey with an attached predicate. This combination can never correspond to a real index — the primary key index is never partial — and Self::validate always rejects it. It stays representable (rather than prevented at the type level) so that rejection is a normal runtime CratestackError, not a call that can’t even be written. Reached via ConflictTarget::PRIMARY_KEY.where_index(<predicate>); not normally constructed directly.

Implementations

impl ConflictTarget

pub const PRIMARY_KEY: Self = Self::PrimaryKey

ConflictTarget::PrimaryKey as an associated const, matching the naming convention Self::columns sets for Columns. Kept alongside the PrimaryKey variant itself (both spellings are used across this codebase’s call sites and tests).

pub const fn columns(cols: &'static [&'static str]) -> Self

Sugar for ConflictTarget::Columns(&[...]).

pub const fn where_index(self, predicate: &'static str) -> Self

Attach a partial-unique-index predicate, e.g. ConflictTarget::columns(&["k"]).where_index("status = 'active'") for an index declared as UNIQUE (k) WHERE status = 'active'.

Only valid when chained onto Self::Columns/Self::columns — the primary key index is never partial, so chaining this onto Self::PrimaryKey/Self::PRIMARY_KEY is rejected by Self::validate rather than silently dropped. This method itself stays infallible (const fn, so it can be used in a const builder chain) — the rejection happens where the target is actually consumed, before any SQL is built.

pub const fn predicate(&self) -> Option<&'static str>

The attached partial-index predicate, if any.

pub const fn is_primary_key(&self) -> bool

true when this target is the model’s primary key.

pub const fn as_columns(&self) -> Option<&'static [&'static str]>

The column tuple, if this target is Self::Columns / Self::columns (predicated or not); None for Self::PrimaryKey/Self::PRIMARY_KEY.

pub fn validate(&self) -> Result<(), CratestackError>

Reject a predicate paired with the primary key target — the PK index is never partial, so that combination can never correspond to a real index. Every runtime entry point that consumes a ConflictTarget calls this before doing any SQL work, so the rejection is a clear CratestackError::Validation, not a silently dropped predicate or a confusing database-side error.

Trait Implementations

impl Clone for ConflictTarget

fn clone(&self) -> ConflictTarget

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for ConflictTarget

impl Debug for ConflictTarget

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

Formats the value using the given formatter.

impl Default for ConflictTarget

fn default() -> ConflictTarget

Returns the “default value” for a type.

impl Eq for ConflictTarget

impl PartialEq for ConflictTarget

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for ConflictTarget