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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the License for the
// specific language governing permissions and limitations
// under the License.
//! Utility functions for complex field access
use arrow::datatypes::{DataType, Field};
use datafusion_common::{
plan_datafusion_err, plan_err, DataFusionError, Result, ScalarValue,
};
/// Types of the field access expression of a nested type, such as `Field` or `List`
pub enum GetFieldAccessSchema {
/// Named field, For example `struct["name"]`
NamedStructField { name: ScalarValue },
/// Single list index, for example: `list[i]`
ListIndex { key_dt: DataType },
/// List range, for example `list[i:j]`
ListRange {
start_dt: DataType,
stop_dt: DataType,
},
}
impl GetFieldAccessSchema {
/// Returns the schema [`Field`] from a [`DataType::List`] or
/// [`DataType::Struct`] indexed by this structure
///
/// # Error
/// Errors if
/// * the `data_type` is not a Struct or a List,
/// * the `data_type` of the name/index/start-stop do not match a supported index type
pub fn get_accessed_field(&self, data_type: &DataType) -> Result<Field> {
match self {
Self::NamedStructField{ name } => {
match (data_type, name) {
(DataType::Map(fields, _), _) => {
match fields.data_type() {
DataType::Struct(fields) if fields.len() == 2 => {
// Arrow's MapArray is essentially a ListArray of structs with two columns. They are
// often named "key", and "value", but we don't require any specific naming here;
// instead, we assume that the second columnis the "value" column both here and in
// execution.
let value_field = fields.get(1).expect("fields should have exactly two members");
Ok(Field::new("map", value_field.data_type().clone(), true))
},
_ => plan_err!("Map fields must contain a Struct with exactly 2 fields"),
}
}
(DataType::Struct(fields), ScalarValue::Utf8(Some(s))) => {
if s.is_empty() {
plan_err!(
"Struct based indexed access requires a non empty string"
)
} else {
let field = fields.iter().find(|f| f.name() == s);
field.ok_or(plan_datafusion_err!("Field {s} not found in struct")).map(|f| f.as_ref().clone())
}
}
(DataType::Struct(_), _) => plan_err!(
"Only utf8 strings are valid as an indexed field in a struct"
),
(other, _) => plan_err!("The expression to get an indexed field is only valid for `List`, `Struct`, or `Map` types, got {other}"),
}
}
Self::ListIndex{ key_dt } => {
match (data_type, key_dt) {
(DataType::List(lt), DataType::Int64) => Ok(Field::new("list", lt.data_type().clone(), true)),
(DataType::List(_), _) => plan_err!(
"Only ints are valid as an indexed field in a list"
),
(other, _) => plan_err!("The expression to get an indexed field is only valid for `List` or `Struct` types, got {other}"),
}
}
Self::ListRange{ start_dt, stop_dt } => {
match (data_type, start_dt, stop_dt) {
(DataType::List(_), DataType::Int64, DataType::Int64) => Ok(Field::new("list", data_type.clone(), true)),
(DataType::List(_), _, _) => plan_err!(
"Only ints are valid as an indexed field in a list"
),
(other, _, _) => plan_err!("The expression to get an indexed field is only valid for `List` or `Struct` types, got {other}"),
}
}
}
}
}