SeaQL/sea-orm · error

Already checked arity

Error message

Already checked arity

What it means

`primary_key_identity` builds the primary key Identity by iterating PrimaryKey columns, after asserting arity via `PrimaryKeyArity::ARITY`. The macro's `.expect("Already checked arity")` (src/entity/base_entity.rs:344) fires if the iterator is exhausted despite the declared ARITY — i.e. the PrimaryKey enum and its ARITY disagree.

Source

Thrown at src/entity/base_entity.rs:344

        let mut keys = Self::PrimaryKey::iter();
        for v in values.into().into_value_tuple() {
            if let Some(key) = keys.next() {
                let col = key.into_column();
                select = select.filter(col.eq(v));
            } else {
                unreachable!("primary key arity mismatch");
            }
        }
        select
    }

    /// Get primary key as Identity
    fn primary_key_identity() -> Identity {
        let mut cols = Self::PrimaryKey::iter();
        macro_rules! next {
            () => {
                cols.next()
                    .expect("Already checked arity")
                    .into_column()
                    .as_column_ref()
                    .1
            };
        }
        match <<Self::PrimaryKey as PrimaryKeyTrait>::ValueType as PrimaryKeyArity>::ARITY {
            1 => {
                let s1 = next!();
                Identity::Unary(s1)
            }
            2 => {
                let s1 = next!();
                let s2 = next!();
                Identity::Binary(s1, s2)
            }
            3 => {
                let s1 = next!();
                let s2 = next!();

View on GitHub (pinned to e29bcd1b41)

Solutions

1. Regenerate entities with sea-orm-cli so derive macros produce consistent PrimaryKey and arity.
2. Remove manual PrimaryKeyTrait impls and rely on DeriveEntityModel.
3. Ensure each `#[sea_orm(primary_key)]` column is kept in sync when altering schemas.
4. Report to SeaORM if reproducible with purely generated code.

// check primary key arity matches the actual primary key column count
let declared = <<Entity::PrimaryKey as PrimaryKeyTrait>::ValueType as PrimaryKeyArity>::ARITY;
assert_eq!(declared as usize, Entity::PrimaryKey::iter().count());

fn primary_key_consistent<E: EntityTrait>() -> bool {
    <<E::PrimaryKey as PrimaryKeyTrait>::ValueType as PrimaryKeyArity>::ARITY as usize
        == E::PrimaryKey::iter().count()
}

When it happens

Trigger: An entity whose PrimaryKey definition's ValueType arity (1 or composite) does not match the number of `#[sea_orm(primary_key)]` columns — typically only via macro/codegen bugs or hand-rolled PrimaryKeyTrait implementations.

Common situations: Manually implementing PrimaryKeyTrait instead of deriving it; editing generated entities to add/remove primary key columns without updating arity; SeaORM version upgrades where generated code differs.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• Already checked arity
• item is a full model
• item is a full model
• Must be valid
• Already checked arity

AI-assisted analysis of SeaQL/sea-orm@e29bcd1b41 (2026-09-10). Data as JSON: /api/errors/899aa77d0c7a5095. Report an issue: GitHub.