dbt-labs/dbt-core · error

this must be a BaseRelation object

Error message

this must be a BaseRelation object

What it means

The Jinja object being unwrapped exists, but the value stored under its __this__ key does not downcast to RelationObject — i.e. someone constructed a relation-like dict whose payload is not a BaseRelation wrapper, so the inner Arc<dyn BaseRelation> cannot be recovered.

Solutions

1. Ensure the object stored under __this__ is a RelationObject wrapping a BaseRelation
2. Avoid hand-constructing relation-like dicts; use the Relation wrapper API
3. Type-check the __this__ payload before downcasting

When it happens

Trigger: Thrown at crates/dbt-adapter/src/cast_util.rs:29 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of dbt-labs/dbt-core@0267ce9170 (2026-09-07). Data as JSON: /api/errors/b5e1c004b3012283. Report an issue: GitHub.

Appendix: source

Thrown at crates/dbt-adapter/src/cast_util.rs:29

pub fn downcast_value_to_dyn_base_relation(
    value: &minijinja::Value,
) -> Result<Arc<dyn BaseRelation>, minijinja::Error> {
    if let Some(relation_object) = value.downcast_object::<RelationObject>() {
        Ok(relation_object.inner())
    } else if let Some(relation_object) = value
        .as_object()
        .ok_or_else(|| {
            minijinja::Error::new(
                minijinja::ErrorKind::InvalidOperation,
                "relation must be an object",
            )
        })?
        .get_value(&minijinja::Value::from(THIS_RELATION_KEY))
    {
        Ok(relation_object
            .downcast_object::<RelationObject>()
            .ok_or_else(|| {
                minijinja::Error::new(
                    minijinja::ErrorKind::InvalidOperation,
                    "this must be a BaseRelation object",
                )
            })?
            .inner())
    } else {
        Err(minijinja::Error::new(
            minijinja::ErrorKind::InvalidOperation,
            format!(
                "Unsupported relation type ({}) in {}:{}",
                value,
                file!(),
                line!()
            ),
        ))
    }
}

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