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Implement arrow_json encoder for Decimal128 & Decimal256 #6606

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merged 5 commits into from
Oct 21, 2024
Merged

Implement arrow_json encoder for Decimal128 & Decimal256 #6606

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9199997
Implement arrow_json encoder for Decimal128 & Decimal256
phillipleblanc Oct 21, 2024
ae0b9f8
fix
phillipleblanc Oct 21, 2024
dfe8edb
Use primitive helper for i128
phillipleblanc Oct 21, 2024
fc86a77
Revert "Use primitive helper for i128"
phillipleblanc Oct 21, 2024
c912fa1
Use ArrayFormatter directly
tustvold Oct 21, 2024
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44 changes: 44 additions & 0 deletions arrow-json/src/writer/encoder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -134,6 +134,16 @@ fn make_encoder_impl<'a>(
};
(Box::new(encoder) as _, array.nulls().cloned())
}
DataType::Decimal128(_, _) => {
let array = array.as_any().downcast_ref::<Decimal128Array>()
.ok_or_else(|| ArrowError::InvalidArgumentError("Expected Decimal128Array".to_string()))?;
(Box::new(Decimal128Encoder::new(array)) as _, array.nulls().cloned())
}
DataType::Decimal256(_, _) => {
let array = array.as_any().downcast_ref::<Decimal256Array>()
.ok_or_else(|| ArrowError::InvalidArgumentError("Expected Decimal256Array".to_string()))?;
(Box::new(Decimal256Encoder::new(array)) as _, array.nulls().cloned())
}
d => match d.is_temporal() {
true => {
// Note: the implementation of Encoder for ArrayFormatter assumes it does not produce
Expand Down Expand Up @@ -545,3 +555,37 @@ where
out.push(b'"');
}
}

struct Decimal128Encoder<'a> {
array: &'a Decimal128Array,
}

impl<'a> Decimal128Encoder<'a> {
fn new(array: &'a Decimal128Array) -> Self {
Self { array }
}
}

impl<'a> Encoder for Decimal128Encoder<'a> {
fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
let formatted = self.array.value_as_string(idx);
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FWIW you can avoid this allocation by using https://docs.rs/arrow-cast/latest/arrow_cast/display/struct.ArrayFormatter.html

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Let me try this

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I tried this, but it encoded them as strings not numbers, and I don't see any option that is relevant.

DataType::Decimal128(_, _) | DataType::Decimal256(_, _)=> {
            let options = FormatOptions::new();
            let formatter = ArrayFormatter::try_new(array, &options)?;
            (Box::new(formatter) as _, array.nulls().cloned())
        }
assertion `left == right` failed
  left: [Some(Object {"decimal": Number(12.34)}), Some(Object {"decimal": Number(56.78)}), Some(Object {"decimal": Number(90.12)}), None]
 right: [Some(Object {"decimal": String("12.34")}), Some(Object {"decimal": String("56.78")}), Some(Object {"decimal": String("90.12")}), None]

I'm not sure why though, it seems to call the same format_decimal method that value_as_string does?

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Yes you will need to keep the custom encoder as a newtype as unlike the implementation for ArrayFormatter above, you don't want to write the quote characters

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I took the liberty of doing this in c912fa1

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Thanks!

out.extend_from_slice(formatted.as_bytes());
}
}

struct Decimal256Encoder<'a> {
array: &'a Decimal256Array,
}

impl<'a> Decimal256Encoder<'a> {
fn new(array: &'a Decimal256Array) -> Self {
Self { array }
}
}

impl<'a> Encoder for Decimal256Encoder<'a> {
fn encode(&mut self, idx: usize, out: &mut Vec<u8>) {
let formatted = self.array.value_as_string(idx);
out.extend_from_slice(formatted.as_bytes());
}
}
78 changes: 77 additions & 1 deletion arrow-json/src/writer/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -405,7 +405,7 @@ mod tests {

use arrow_array::builder::*;
use arrow_array::types::*;
use arrow_buffer::{Buffer, NullBuffer, OffsetBuffer, ToByteSlice};
use arrow_buffer::{i256, Buffer, NullBuffer, OffsetBuffer, ToByteSlice};
use arrow_data::ArrayData;

use crate::reader::*;
Expand Down Expand Up @@ -1833,4 +1833,80 @@ mod tests {
r#"[{"my_dict":"a"},{"my_dict":null},{"my_dict":null}]"#
)
}

#[test]
fn test_decimal128_encoder() {
let array = Decimal128Array::from_iter_values([1234, 5678, 9012])
.with_precision_and_scale(10, 2)
.unwrap();
let field = Arc::new(Field::new("decimal", array.data_type().clone(), true));
let schema = Schema::new(vec![field]);
let batch = RecordBatch::try_new(Arc::new(schema), vec![Arc::new(array)]).unwrap();

let mut buf = Vec::new();
{
let mut writer = LineDelimitedWriter::new(&mut buf);
writer.write_batches(&[&batch]).unwrap();
}

assert_json_eq(
&buf,
r#"{"decimal":12.34}
{"decimal":56.78}
{"decimal":90.12}
"#,
);
}

#[test]
fn test_decimal256_encoder() {
let array = Decimal256Array::from_iter_values([
i256::from(123400),
i256::from(567800),
i256::from(901200),
])
.with_precision_and_scale(10, 4)
.unwrap();
let field = Arc::new(Field::new("decimal", array.data_type().clone(), true));
let schema = Schema::new(vec![field]);
let batch = RecordBatch::try_new(Arc::new(schema), vec![Arc::new(array)]).unwrap();

let mut buf = Vec::new();
{
let mut writer = LineDelimitedWriter::new(&mut buf);
writer.write_batches(&[&batch]).unwrap();
}

assert_json_eq(
&buf,
r#"{"decimal":12.3400}
{"decimal":56.7800}
{"decimal":90.1200}
"#,
);
}

#[test]
fn test_decimal_encoder_with_nulls() {
let array = Decimal128Array::from_iter([Some(1234), None, Some(5678)])
.with_precision_and_scale(10, 2)
.unwrap();
let field = Arc::new(Field::new("decimal", array.data_type().clone(), true));
let schema = Schema::new(vec![field]);
let batch = RecordBatch::try_new(Arc::new(schema), vec![Arc::new(array)]).unwrap();

let mut buf = Vec::new();
{
let mut writer = LineDelimitedWriter::new(&mut buf);
writer.write_batches(&[&batch]).unwrap();
}

assert_json_eq(
&buf,
r#"{"decimal":12.34}
{}
{"decimal":56.78}
"#,
);
}
}
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