Function cast_dictionary_column

datafusion/common/src/nested_struct.rs:267–307

(
    source_col: &ArrayRef,
    source_key_type: &DataType,
    target_key_type: &DataType,
    target_value_type: &DataType,
    cast_options: &CastOptions,
)

}

fn cast_dictionary_column(
    source_col: &ArrayRef,
    source_key_type: &DataType,
    target_key_type: &DataType,
    target_value_type: &DataType,
    cast_options: &CastOptions,
) -> Result<ArrayRef> {
    // Dispatch on source key type to access keys/values, then recursively
    // cast values. Rebuild with the source key type first.
    macro_rules! cast_dict_values {
        ($t:ty) => {{
            let source_dict = source_col
                .as_any()
                .downcast_ref::<DictionaryArray<$t>>()
                .expect("downcast must succeed");
            let cast_values =
                cast_column(source_dict.values(), target_value_type, cast_options)?;
            Ok(Arc::new(DictionaryArray::<$t>::new(
                source_dict.keys().clone(),
                cast_values,
            )) as ArrayRef)
        }};
    }

    let result: Result<ArrayRef> = downcast_integer! {
        source_key_type => (cast_dict_values),
        k => _plan_err!("Unsupported dictionary key type: {k}")
    };
    let result = result?;

    // If key types differ, delegate key casting to Arrow.
    if source_key_type != target_key_type {
        let target_dict_type = DataType::Dictionary(
            Box::new(target_key_type.clone()),
            Box::new(target_value_type.clone()),
        );
        Ok(cast_with_options(&result, &target_dict_type, cast_options)?)
    } else {
        Ok(result)
    }
}

/// Validates compatibility between source and target struct fields for casting operations.
///