2.0.0-rc.43

Release Notes: SeaORM 2.0.0-rc.43

(since 2.0.0-rc.42)

New Features

BelongsTo relation type (#3118, #3133, #3134)

A dedicated BelongsTo<E> / BelongsTo<Option<E>> type for belongs_to relations,
alongside the existing HasOne. Cardinality lives in the type parameter, so the
foreign-key nullability is expressed — and checked — at compile time:

• BelongsTo<E> — the FK is NOT NULL; the relation cannot be detached (there is
  no way to set it to "none" on the active side), so orphaning a required parent is
  a compile error rather than a runtime constraint violation.
• BelongsTo<Option<E>> — the FK is nullable; the relation can be detached, which
  nulls the FK on save.

The cardinality is validated against the FK columns when the entity is derived:
BelongsTo<Entity> requires every from column to be NOT NULL, and
BelongsTo<Option<Entity>> requires at least one nullable from column — a mismatch
is a compile error. Composite foreign keys with mixed nullability detach by nulling
only their nullable columns.

#[sea_orm(belongs_to, from = "user_id", to = "id")]
pub author: BelongsTo<super::user::Entity>,          // required

#[sea_orm(belongs_to, from = "bakery_id", to = "id")]
pub bakery: BelongsTo<Option<super::bakery::Entity>>, // optional

The active side is ActiveBelongsTo<..>, mirroring ActiveHasOne / ActiveHasMany.

HasOne still works for belongs_to — no migration required (#3133)

Adopting BelongsTo is opt-in. A belongs_to field may keep its existing
HasOne<Entity> type; it continues to compile and behave as before. Use BelongsTo
when you want the compile-time cardinality guarantee; otherwise nothing changes.

Enhancements

CLI lists valid options on generation error (#3131)

sea-orm-cli generate entity now prints the valid choices when an invalid option
value is supplied, instead of only reporting that the value was rejected.

Bug Fixes

has_related with a Condition::any() filter (#3126)

has_related wrapped the caller's condition and then added the mandatory FK/join
condition to it. When the caller passed a Condition::any() (an OR group), the
join condition was folded into that disjunction, so the relation constraint was no
longer guaranteed. The caller's condition is now wrapped in Condition::all() first,
yielding (caller condition) AND (fk join) regardless of any() / all().

Entity codegen for PostgreSQL enum array columns (#3120)

Array-of-enum columns were generated as scalar active-enum fields because the type
resolver unwrapped Array(Enum) to Enum. Array columns now route through the
full type resolver, so enum[] columns generate Vec<Enum> fields.

Compatibility Notes

• belongs_to relations may now be typed BelongsTo<Entity> /
  BelongsTo<Option<Entity>>. This is opt-in — existing HasOne-typed belongs_to
  fields are unchanged and still supported. sea-orm-cli continues to generate the
  HasOne form.
• The compile-time detach guarantee applies only to BelongsTo<Entity> (non-null);
  it is a property of the type, so it costs nothing at runtime.
• A BelongsTo field's type parameter must match its FK nullability (checked when
  the entity is derived). This only affects code that opts into BelongsTo.
• The nested-ActiveModel relation types remain semver-exempt (unstable): rc.43
  drops their PartialEq<Option<..>> impls, so compare an empty relation with
  is_unloaded_or_not_found() / is_not_found() / as_ref() rather than == None
  / == Some(..).