field_util.rs

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//! Utility functions for complex field access

use arrow::datatypes::{DataType, Field};

use crate::error::{DataFusionError, Result};
use crate::scalar::ScalarValue;

/// Returns the field access indexed by `key` from a [`DataType::List`]
/// # Error
/// Errors if
/// * the `data_type` is not a Struct or,
/// * there is no field key is not of the required index type
pub fn get_indexed_field(data_type: &DataType, key: &ScalarValue) -> Result<Field> {
    match (data_type, key) {
        (DataType::List(lt), ScalarValue::Int64(Some(i))) => {
            if *i < 0 {
                Err(DataFusionError::Plan(format!(
                    "List based indexed access requires a positive int, was {0}",
                    i
                )))
            } else {
                Ok(Field::new(&i.to_string(), lt.data_type().clone(), false))
            }
        }
        (DataType::List(_), _) => Err(DataFusionError::Plan(
            "Only ints are valid as an indexed field in a list".to_string(),
        )),
        _ => Err(DataFusionError::Plan(
            "The expression to get an indexed field is only valid for `List` types"
                .to_string(),
        )),
    }
}