datafusion_physical_expr/expressions/

try_cast.rs

// 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.

use std::fmt;
use std::hash::Hash;
use std::sync::Arc;

use crate::PhysicalExpr;
use arrow::compute;
use arrow::compute::CastOptions;
use arrow::datatypes::{DataType, FieldRef, Schema};
use arrow::record_batch::RecordBatch;
use compute::can_cast_types;
use datafusion_common::format::DEFAULT_FORMAT_OPTIONS;
use datafusion_common::{Result, not_impl_err};
use datafusion_expr::ColumnarValue;

/// TRY_CAST expression casts an expression to a specific data type and returns NULL on invalid cast
#[derive(Debug, Eq)]
pub struct TryCastExpr {
    /// The expression to cast
    expr: Arc<dyn PhysicalExpr>,
    /// The data type to cast to
    cast_type: DataType,
}

// Manually derive PartialEq and Hash to work around https://github.com/rust-lang/rust/issues/78808
impl PartialEq for TryCastExpr {
    fn eq(&self, other: &Self) -> bool {
        self.expr.eq(&other.expr) && self.cast_type == other.cast_type
    }
}

impl Hash for TryCastExpr {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.expr.hash(state);
        self.cast_type.hash(state);
    }
}

impl TryCastExpr {
    /// Create a new CastExpr
    pub fn new(expr: Arc<dyn PhysicalExpr>, cast_type: DataType) -> Self {
        Self { expr, cast_type }
    }

    /// The expression to cast
    pub fn expr(&self) -> &Arc<dyn PhysicalExpr> {
        &self.expr
    }

    /// The data type to cast to
    pub fn cast_type(&self) -> &DataType {
        &self.cast_type
    }
}

impl fmt::Display for TryCastExpr {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "TRY_CAST({} AS {})", self.expr, self.cast_type)
    }
}

impl PhysicalExpr for TryCastExpr {
    fn data_type(&self, _input_schema: &Schema) -> Result<DataType> {
        Ok(self.cast_type.clone())
    }

    fn nullable(&self, _input_schema: &Schema) -> Result<bool> {
        Ok(true)
    }

    fn evaluate(&self, batch: &RecordBatch) -> Result<ColumnarValue> {
        let value = self.expr.evaluate(batch)?;
        let options = CastOptions {
            safe: true,
            format_options: DEFAULT_FORMAT_OPTIONS,
        };
        value.cast_to(&self.cast_type, Some(&options))
    }

    fn return_field(&self, input_schema: &Schema) -> Result<FieldRef> {
        self.expr
            .return_field(input_schema)
            .map(|f| f.as_ref().clone().with_data_type(self.cast_type.clone()))
            .map(Arc::new)
    }

    fn children(&self) -> Vec<&Arc<dyn PhysicalExpr>> {
        vec![&self.expr]
    }

    fn with_new_children(
        self: Arc<Self>,
        children: Vec<Arc<dyn PhysicalExpr>>,
    ) -> Result<Arc<dyn PhysicalExpr>> {
        Ok(Arc::new(TryCastExpr::new(
            Arc::clone(&children[0]),
            self.cast_type.clone(),
        )))
    }

    fn fmt_sql(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "TRY_CAST(")?;
        self.expr.fmt_sql(f)?;
        write!(f, " AS {:?})", self.cast_type)
    }
}

/// Return a PhysicalExpression representing `expr` casted to
/// `cast_type`, if any casting is needed.
///
/// Note that such casts may lose type information
pub fn try_cast(
    expr: Arc<dyn PhysicalExpr>,
    input_schema: &Schema,
    cast_type: DataType,
) -> Result<Arc<dyn PhysicalExpr>> {
    let expr_type = expr.data_type(input_schema)?;
    if expr_type == cast_type {
        Ok(Arc::clone(&expr))
    } else if can_cast_types(&expr_type, &cast_type) {
        Ok(Arc::new(TryCastExpr::new(expr, cast_type)))
    } else {
        not_impl_err!("Unsupported TRY_CAST from {expr_type} to {cast_type}")
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::expressions::col;
    use arrow::array::{
        Decimal128Array, Decimal128Builder, StringArray, Time64NanosecondArray,
    };
    use arrow::{
        array::{
            Array, Float32Array, Float64Array, Int8Array, Int16Array, Int32Array,
            Int64Array, TimestampNanosecondArray, UInt32Array,
        },
        datatypes::*,
    };
    use datafusion_physical_expr_common::physical_expr::fmt_sql;

    // runs an end-to-end test of physical type cast
    // 1. construct a record batch with a column "a" of type A
    // 2. construct a physical expression of TRY_CAST(a AS B)
    // 3. evaluate the expression
    // 4. verify that the resulting expression is of type B
    // 5. verify that the resulting values are downcastable and correct
    macro_rules! generic_decimal_to_other_test_cast {
        ($DECIMAL_ARRAY:ident, $A_TYPE:expr, $TYPEARRAY:ident, $TYPE:expr, $VEC:expr) => {{
            let schema = Schema::new(vec![Field::new("a", $A_TYPE, true)]);
            let batch = RecordBatch::try_new(
                Arc::new(schema.clone()),
                vec![Arc::new($DECIMAL_ARRAY)],
            )?;
            // verify that we can construct the expression
            let expression = try_cast(col("a", &schema)?, &schema, $TYPE)?;

            // verify that its display is correct
            assert_eq!(
                format!("TRY_CAST(a@0 AS {})", $TYPE),
                format!("{}", expression)
            );

            // verify that the expression's type is correct
            assert_eq!(expression.data_type(&schema)?, $TYPE);

            // compute
            let result = expression
                .evaluate(&batch)?
                .into_array(batch.num_rows())
                .expect("Failed to convert to array");

            // verify that the array's data_type is correct
            assert_eq!(*result.data_type(), $TYPE);

            // verify that the data itself is downcastable
            let result = result
                .as_any()
                .downcast_ref::<$TYPEARRAY>()
                .expect("failed to downcast");

            // verify that the result itself is correct
            for (i, x) in $VEC.iter().enumerate() {
                match x {
                    Some(x) => assert_eq!(result.value(i), *x),
                    None => assert!(result.is_null(i)),
                }
            }
        }};
    }

    // runs an end-to-end test of physical type cast
    // 1. construct a record batch with a column "a" of type A
    // 2. construct a physical expression of TRY_CAST(a AS B)
    // 3. evaluate the expression
    // 4. verify that the resulting expression is of type B
    // 5. verify that the resulting values are downcastable and correct
    macro_rules! generic_test_cast {
        ($A_ARRAY:ident, $A_TYPE:expr, $A_VEC:expr, $TYPEARRAY:ident, $TYPE:expr, $VEC:expr) => {{
            let schema = Schema::new(vec![Field::new("a", $A_TYPE, true)]);
            let a_vec_len = $A_VEC.len();
            let a = $A_ARRAY::from($A_VEC);
            let batch =
                RecordBatch::try_new(Arc::new(schema.clone()), vec![Arc::new(a)])?;

            // verify that we can construct the expression
            let expression = try_cast(col("a", &schema)?, &schema, $TYPE)?;

            // verify that its display is correct
            assert_eq!(
                format!("TRY_CAST(a@0 AS {})", $TYPE),
                format!("{}", expression)
            );

            // verify that the expression's type is correct
            assert_eq!(expression.data_type(&schema)?, $TYPE);

            // compute
            let result = expression
                .evaluate(&batch)?
                .into_array(batch.num_rows())
                .expect("Failed to convert to array");

            // verify that the array's data_type is correct
            assert_eq!(*result.data_type(), $TYPE);

            // verify that the len is correct
            assert_eq!(result.len(), a_vec_len);

            // verify that the data itself is downcastable
            let result = result
                .as_any()
                .downcast_ref::<$TYPEARRAY>()
                .expect("failed to downcast");

            // verify that the result itself is correct
            for (i, x) in $VEC.iter().enumerate() {
                match x {
                    Some(x) => assert_eq!(result.value(i), *x),
                    None => assert!(result.is_null(i)),
                }
            }
        }};
    }

    #[test]
    fn test_try_cast_decimal_to_decimal() -> Result<()> {
        // try cast one decimal data type to another decimal data type
        let array: Vec<i128> = vec![1234, 2222, 3, 4000, 5000];
        let decimal_array = create_decimal_array(&array, 10, 3);
        generic_decimal_to_other_test_cast!(
            decimal_array,
            DataType::Decimal128(10, 3),
            Decimal128Array,
            DataType::Decimal128(20, 6),
            [
                Some(1_234_000),
                Some(2_222_000),
                Some(3_000),
                Some(4_000_000),
                Some(5_000_000),
                None
            ]
        );

        let decimal_array = create_decimal_array(&array, 10, 3);
        generic_decimal_to_other_test_cast!(
            decimal_array,
            DataType::Decimal128(10, 3),
            Decimal128Array,
            DataType::Decimal128(10, 2),
            [Some(123), Some(222), Some(0), Some(400), Some(500), None]
        );

        Ok(())
    }

    #[test]
    fn test_try_cast_decimal_to_numeric() -> Result<()> {
        // TODO we should add function to create Decimal128Array with value and metadata
        // https://github.com/apache/arrow-rs/issues/1009
        let array: Vec<i128> = vec![1, 2, 3, 4, 5];
        let decimal_array = create_decimal_array(&array, 10, 0);
        // decimal to i8
        generic_decimal_to_other_test_cast!(
            decimal_array,
            DataType::Decimal128(10, 0),
            Int8Array,
            DataType::Int8,
            [
                Some(1_i8),
                Some(2_i8),
                Some(3_i8),
                Some(4_i8),
                Some(5_i8),
                None
            ]
        );

        // decimal to i16
        let decimal_array = create_decimal_array(&array, 10, 0);
        generic_decimal_to_other_test_cast!(
            decimal_array,
            DataType::Decimal128(10, 0),
            Int16Array,
            DataType::Int16,
            [
                Some(1_i16),
                Some(2_i16),
                Some(3_i16),
                Some(4_i16),
                Some(5_i16),
                None
            ]
        );

        // decimal to i32
        let decimal_array = create_decimal_array(&array, 10, 0);
        generic_decimal_to_other_test_cast!(
            decimal_array,
            DataType::Decimal128(10, 0),
            Int32Array,
            DataType::Int32,
            [
                Some(1_i32),
                Some(2_i32),
                Some(3_i32),
                Some(4_i32),
                Some(5_i32),
                None
            ]
        );

        // decimal to i64
        let decimal_array = create_decimal_array(&array, 10, 0);
        generic_decimal_to_other_test_cast!(
            decimal_array,
            DataType::Decimal128(10, 0),
            Int64Array,
            DataType::Int64,
            [
                Some(1_i64),
                Some(2_i64),
                Some(3_i64),
                Some(4_i64),
                Some(5_i64),
                None
            ]
        );

        // decimal to float32
        let array: Vec<i128> = vec![1234, 2222, 3, 4000, 5000];
        let decimal_array = create_decimal_array(&array, 10, 3);
        generic_decimal_to_other_test_cast!(
            decimal_array,
            DataType::Decimal128(10, 3),
            Float32Array,
            DataType::Float32,
            [
                Some(1.234_f32),
                Some(2.222_f32),
                Some(0.003_f32),
                Some(4.0_f32),
                Some(5.0_f32),
                None
            ]
        );
        // decimal to float64
        let decimal_array = create_decimal_array(&array, 20, 6);
        generic_decimal_to_other_test_cast!(
            decimal_array,
            DataType::Decimal128(20, 6),
            Float64Array,
            DataType::Float64,
            [
                Some(0.001234_f64),
                Some(0.002222_f64),
                Some(0.000003_f64),
                Some(0.004_f64),
                Some(0.005_f64),
                None
            ]
        );

        Ok(())
    }

    #[test]
    fn test_try_cast_numeric_to_decimal() -> Result<()> {
        // int8
        generic_test_cast!(
            Int8Array,
            DataType::Int8,
            vec![1, 2, 3, 4, 5],
            Decimal128Array,
            DataType::Decimal128(3, 0),
            [Some(1), Some(2), Some(3), Some(4), Some(5)]
        );

        // int16
        generic_test_cast!(
            Int16Array,
            DataType::Int16,
            vec![1, 2, 3, 4, 5],
            Decimal128Array,
            DataType::Decimal128(5, 0),
            [Some(1), Some(2), Some(3), Some(4), Some(5)]
        );

        // int32
        generic_test_cast!(
            Int32Array,
            DataType::Int32,
            vec![1, 2, 3, 4, 5],
            Decimal128Array,
            DataType::Decimal128(10, 0),
            [Some(1), Some(2), Some(3), Some(4), Some(5)]
        );

        // int64
        generic_test_cast!(
            Int64Array,
            DataType::Int64,
            vec![1, 2, 3, 4, 5],
            Decimal128Array,
            DataType::Decimal128(20, 0),
            [Some(1), Some(2), Some(3), Some(4), Some(5)]
        );

        // int64 to different scale
        generic_test_cast!(
            Int64Array,
            DataType::Int64,
            vec![1, 2, 3, 4, 5],
            Decimal128Array,
            DataType::Decimal128(20, 2),
            [Some(100), Some(200), Some(300), Some(400), Some(500)]
        );

        // float32
        generic_test_cast!(
            Float32Array,
            DataType::Float32,
            vec![1.5, 2.5, 3.0, 1.123_456_8, 5.50],
            Decimal128Array,
            DataType::Decimal128(10, 2),
            [Some(150), Some(250), Some(300), Some(112), Some(550)]
        );

        // float64
        generic_test_cast!(
            Float64Array,
            DataType::Float64,
            vec![1.5, 2.5, 3.0, 1.123_456_8, 5.50],
            Decimal128Array,
            DataType::Decimal128(20, 4),
            [
                Some(15000),
                Some(25000),
                Some(30000),
                Some(11235),
                Some(55000)
            ]
        );
        Ok(())
    }

    #[test]
    fn test_cast_i32_u32() -> Result<()> {
        generic_test_cast!(
            Int32Array,
            DataType::Int32,
            vec![1, 2, 3, 4, 5],
            UInt32Array,
            DataType::UInt32,
            [
                Some(1_u32),
                Some(2_u32),
                Some(3_u32),
                Some(4_u32),
                Some(5_u32)
            ]
        );
        Ok(())
    }

    #[test]
    fn test_cast_i32_utf8() -> Result<()> {
        generic_test_cast!(
            Int32Array,
            DataType::Int32,
            vec![1, 2, 3, 4, 5],
            StringArray,
            DataType::Utf8,
            [Some("1"), Some("2"), Some("3"), Some("4"), Some("5")]
        );
        Ok(())
    }

    #[test]
    fn test_try_cast_utf8_i32() -> Result<()> {
        generic_test_cast!(
            StringArray,
            DataType::Utf8,
            vec!["a", "2", "3", "b", "5"],
            Int32Array,
            DataType::Int32,
            [None, Some(2), Some(3), None, Some(5)]
        );
        Ok(())
    }

    #[test]
    fn test_cast_i64_t64() -> Result<()> {
        let original = vec![1, 2, 3, 4, 5];
        let expected: Vec<Option<i64>> = original
            .iter()
            .map(|i| Some(Time64NanosecondArray::from(vec![*i]).value(0)))
            .collect();
        generic_test_cast!(
            Int64Array,
            DataType::Int64,
            original,
            TimestampNanosecondArray,
            DataType::Timestamp(TimeUnit::Nanosecond, None),
            expected
        );
        Ok(())
    }

    #[test]
    fn invalid_cast() {
        // Ensure a useful error happens at plan time if invalid casts are used
        let schema = Schema::new(vec![Field::new("a", DataType::Int32, false)]);

        let result = try_cast(
            col("a", &schema).unwrap(),
            &schema,
            DataType::Interval(IntervalUnit::MonthDayNano),
        );
        result.expect_err("expected Invalid TRY_CAST");
    }

    // create decimal array with the specified precision and scale
    fn create_decimal_array(array: &[i128], precision: u8, scale: i8) -> Decimal128Array {
        let mut decimal_builder = Decimal128Builder::with_capacity(array.len());
        for value in array {
            decimal_builder.append_value(*value);
        }
        decimal_builder.append_null();
        decimal_builder
            .finish()
            .with_precision_and_scale(precision, scale)
            .unwrap()
    }

    #[test]
    fn test_fmt_sql() -> Result<()> {
        let schema = Schema::new(vec![Field::new("a", DataType::Int32, true)]);

        // Test numeric casting
        let expr = try_cast(col("a", &schema)?, &schema, DataType::Int64)?;
        let display_string = expr.to_string();
        assert_eq!(display_string, "TRY_CAST(a@0 AS Int64)");
        let sql_string = fmt_sql(expr.as_ref()).to_string();
        assert_eq!(sql_string, "TRY_CAST(a AS Int64)");

        // Test string casting
        let schema = Schema::new(vec![Field::new("b", DataType::Utf8, true)]);
        let expr = try_cast(col("b", &schema)?, &schema, DataType::Int32)?;
        let display_string = expr.to_string();
        assert_eq!(display_string, "TRY_CAST(b@0 AS Int32)");
        let sql_string = fmt_sql(expr.as_ref()).to_string();
        assert_eq!(sql_string, "TRY_CAST(b AS Int32)");

        Ok(())
    }
}