BoundaryML/baml · error

Class {} does not have a field: {}

Error message

Class {} does not have a field: {}

What it means

After the class resolves, find_existing_class_field looks up the field on the ClassWalker; if find_field returns None it bails with 'Class {} does not have a field: {}'. The referenced field name is absent from an otherwise valid class.

Source

Thrown at engine/baml-lib/jsonish/src/helpers/mod.rs:80

        .enums(enums)
        .classes(classes)
        .recursive_classes(recursive_classes)
        .structural_recursive_aliases(structural_recursive_aliases)
        .build())
}

fn find_existing_class_field(
    class_name: &str,
    field_name: &str,
    class_walker: &Result<ClassWalker<'_>>,
    env_values: &EvaluationContext<'_>,
) -> Result<(Name, TypeIR, Option<String>, bool)> {
    let Ok(class_walker) = class_walker else {
        anyhow::bail!("Class {} does not exist", class_name);
    };

    let Some(field_walker) = class_walker.find_field(field_name) else {
        anyhow::bail!("Class {} does not have a field: {}", class_name, field_name);
    };

    let name = Name::new_with_alias(field_name.to_string(), field_walker.alias(env_values)?);
    let desc = field_walker.description(env_values)?;
    let r#type = field_walker.r#type();
    let streaming_needed = field_walker.item.attributes.streaming_behavior().needed;
    Ok((name, r#type.clone(), desc, streaming_needed))
}

fn find_enum_value(
    enum_name: &str,
    value_name: &str,
    enum_walker: &Result<EnumWalker<'_>>,
    env_values: &EvaluationContext<'_>,
) -> Result<Option<(Name, Option<String>)>> {
    if enum_walker.is_err() {
        anyhow::bail!("Enum {} does not exist", enum_name);
    }

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Correct the field name in the template/helper call to exactly match the class definition.
2. Check field case-sensitivity against the .baml class declaration.
3. Regenerate clients and search templates for the old field name after renames.
4. Consider adding an alias in the schema if the external name must differ.

Example fix

// before
class UserInfo { userName string }
{{ class_userinfo.username }}
// after
{{ class_userinfo.userName }}

// confirm the field exists before template use
let field_names: Vec<_> = class_walker.find_field_list().iter().map(|f| f.name()).collect();
if !field_names.contains(&field_name.to_string()) {
    return Err(anyhow::anyhow!("field '{}' not in class '{}'; available: {:?}", field_name, class_name, field_names));
}

fn field_exists(w: &ClassWalker, name: &str) -> bool { w.find_field(name).is_some() }

match find_existing_class_field(class_name, field_name, &class_walker, &env) {
    Ok(v) => use_field(v),
    Err(err) => return Err(err.context("fix field name in template to match class definition")),
}

When it happens

Trigger: A template/helper references class.field where the class exists but declares no field with that name (case-sensitive), e.g. accessing ctx or description helpers with a stale field name.

Common situations: Renamed or removed class fields while prompts/templates still use the old name; typos in field names; case sensitivity (e.g. 'userName' vs 'username'); dynamic field access built from strings that drifted from the schema.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• Class {} does not exist
• Enum {} does not exist
• Failed to get template '{}': {}
• Expected a statically defined string, not expression
• Expected a statically defined string, not a template_string

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/1d730c5a99e20460. Report an issue: GitHub.