dbt-labs/dbt-core · error · InvalidArgument

Table.select: key must be a string or an array of strings: {

Error message

Table.select: key must be a string or an array of strings: {e}

What it means

Thrown by `Table.select()` when the `key` argument cannot be interpreted as a string or an array of strings. The library first tries to read the key as a single string; if that fails and the value cannot be iterated as a list, this InvalidArgument error is raised. Agate's `select` requires column names, so anything else (number, dict, non-string elements path) is rejected.

Source

Thrown at crates/dbt-agate/src/table.rs:1091

                //
                //     :param key:
                //         Either the name of a single column to include or a sequence of such
                //         names.
                //     :returns:
                //         A new :class:`.Table`.
                //     """
                // ```
                let iter = ArgsIter::new("Table.select", &["key"], args);
                let key = iter.next_arg::<&Value>()?;
                iter.finish()?;

                let keys = if let Some(single_key) = key.as_str() {
                    Vec::from([single_key.to_string()])
                } else {
                    let iter = match key.try_iter() {
                        Ok(iter) => iter,
                        Err(e) => {
                            return Err(Error::new(
                                ErrorKind::InvalidArgument,
                                format!(
                                    "Table.select: key must be a string or an array of strings: {e}"
                                ),
                            ));
                        }
                    };
                    let mut keys = Vec::new();
                    for v in iter {
                        if let Some(s) = v.as_str() {
                            keys.push(s.to_string());
                        } else {
                            return Err(Error::new(
                                ErrorKind::InvalidArgument,
                                format!(
                                    "Table.select: key must be a string or an array of strings: {v} found instead"
                                ),
                            ));

View on GitHub (pinned to 0267ce9170)

Solutions

Pass column names as a string: `table.select('col')`
Pass a list of strings: `table.select(['col1', 'col2'])`
Cast non-string keys to strings before calling select
Log/inspect the type of the key value being passed

Example fix

// before
table.select(0)
// after
table.select('column_name')  # or table.select(['a', 'b'])

Defensive patterns

Strategy: type-guard

Validate before calling

def ensure_select_key(key):
    if isinstance(key, str):
        return [key]
    if isinstance(key, (list, tuple)) and all(isinstance(k, str) for k in key):
        return list(key)
    raise ValueError('key must be a string or list of strings')

Type guard

def is_str_or_str_list(v):
    return isinstance(v, str) or (isinstance(v, (list, tuple)) and all(isinstance(k, str) for k in v))

Try / catch

try:
    result = table.select(key)
except Exception as e:
    if 'key must be a string or an array of strings' in str(e):
        result = table.select(ensure_select_key(key))
    else:
        raise

Prevention

Always pass column names as strings, never indices
Normalize keys with a helper before calling select
Add unit tests for dynamically built key lists

When it happens

Trigger: Calling `table.select(key)` where `key` is not a str and `key.try_iter()` fails — e.g. an integer, a non-iterable object, or a malformed value passed as the column selector.

Common situations: Passing a column index instead of a column name, passing a tuple/set from scripting, or programmatically building the key list and accidentally passing a scalar.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of dbt-labs/dbt-core@0267ce9170 (2026-09-07). Data as JSON: /api/errors/07be4fcebeff4b27. Report an issue: GitHub.