dbt-labs/dbt-core · error · InvalidOperation

local_md5's argument must be a string

Error message

local_md5's argument must be a string

What it means

`local_md5` hashes strings only; when its single argument is not a string (e.g. a number, boolean, list, or undefined value) the `as_str()` conversion fails and this error is raised. It exists to fail fast rather than hashing a Debug representation that would differ from dbt's expected output.

Solutions

1. Convert to string before hashing: `local_md5(value | string)`
2. Guard undefined variables with a default: `local_md5(var | default(""))`
3. Ensure the source column/variable is a string type upstream

Example fix

// before
{% set h = local_md5(user_id) %}
// after
{% set h = local_md5(user_id | string) %}

{% if value is not string %}{% set value = value | string %}{% endif %}

{% macro as_str(v) %}{% if v is string %}{{ v }}{% else %}{{ v | string }}{% endif %}{% endmacro %}

When it happens

Trigger: Calling `{{ local_md5(123) }}`, `{{ local_md5(my_list) }}`, or `{{ local_md5(undefined_var) }}` — any non-string value, including values rendered from YAML that arrive as ints/bools.

Common situations: Hashing a numeric ID directly from the warehouse, an undefined variable due to a missing config key, or a column value that dbt typed as a number.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• argument 'name' to has_var() has incompatible type; value…
• argument 'name' to var() has incompatible type; value is…
• local_md5 requires exactly 1 argument
• zip_strict requires all arguments to be iterable
• adapter not found in context

AI-assisted analysis of dbt-labs/dbt-core@0267ce9170 (2026-09-07). Data as JSON: /api/errors/8e5ceb6443d224cc. Report an issue: GitHub.

Appendix: source

Thrown at crates/dbt-jinja-utils/src/functions/base.rs:1042

/// Args:
///     value: String to hash
///
/// Example:
/// ```jinja
/// {% set hash = local_md5("hello") %}
/// -- Returns "5d41402abc4b2a76b9719d911017c592"
/// ```
pub fn local_md5_fn() -> impl Fn(&[Value], Kwargs) -> Result<Value, Error> {
    move |args: &[Value], _kwargs: Kwargs| -> Result<Value, Error> {
        if args.len() != 1 {
            return Err(Error::new(
                ErrorKind::InvalidOperation,
                "local_md5 requires exactly 1 argument",
            ));
        }

        let value = args[0].as_str().ok_or_else(|| {
            Error::new(
                ErrorKind::InvalidOperation,
                "local_md5's argument must be a string",
            )
        })?;
        // Create MD5 hasher
        let result = format!("{:x}", md5::compute(value.as_bytes()));
        Ok(Value::from(result))
    }
}

/// Parse a dictionary of lists into a BTreeMap<String, Vec<String>>
fn parse_dict_of_lists(dict: &Value) -> Result<IndexMap<String, Vec<String>>, Error> {
    let mut result = IndexMap::new();

    // Iterate over the keys in the dictionary
    for key in dict.try_iter()? {
        // Get the value associated with the key
        let value = dict.get_item(&key)?;

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