From 83352c475681f596e0f1e811f8c2056aef6179b2 Mon Sep 17 00:00:00 2001
From: Alvaro Viebrantz <aviebrantz@google.com>
Date: Tue, 29 Oct 2024 17:12:26 -0400
Subject: [PATCH] fix(bigquery): parse negative NUMERIC from arrow (#11052)

The `big.Int.SetBytes` method interprets input as an unsigned number, so we lose sign information when parsing using. So Arrow decimal parsing code is simplified by just relying on `big.Rat.SetString` method for parsing.

Towards internal b/376149769
---
 bigquery/arrow.go            | 12 ++++--------
 bigquery/integration_test.go |  8 ++++++++
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/bigquery/arrow.go b/bigquery/arrow.go
index 825256dec0b4..041edf8d96a3 100644
--- a/bigquery/arrow.go
+++ b/bigquery/arrow.go
@@ -241,18 +241,14 @@ func convertArrowValue(col arrow.Array, i int, ft arrow.DataType, fs *FieldSchem
 	case *arrow.Decimal128Type:
 		dft := ft.(*arrow.Decimal128Type)
 		v := col.(*array.Decimal128).Value(i)
-		rat := big.NewRat(1, 1)
-		rat.Num().SetBytes(v.BigInt().Bytes())
-		d := rat.Denom()
-		d.Exp(big.NewInt(10), big.NewInt(int64(dft.Scale)), nil)
+		rat := new(big.Rat)
+		rat.SetString(v.ToString(dft.Scale))
 		return Value(rat), nil
 	case *arrow.Decimal256Type:
 		dft := ft.(*arrow.Decimal256Type)
 		v := col.(*array.Decimal256).Value(i)
-		rat := big.NewRat(1, 1)
-		rat.Num().SetBytes(v.BigInt().Bytes())
-		d := rat.Denom()
-		d.Exp(big.NewInt(10), big.NewInt(int64(dft.Scale)), nil)
+		rat := new(big.Rat)
+		rat.SetString(v.ToString(dft.Scale))
 		return Value(rat), nil
 	case *arrow.ListType:
 		arr := col.(*array.List)
diff --git a/bigquery/integration_test.go b/bigquery/integration_test.go
index df26585fa6f8..649790b2814f 100644
--- a/bigquery/integration_test.go
+++ b/bigquery/integration_test.go
@@ -2167,6 +2167,7 @@ func initQueryParameterTestCases() {
 	dtm := civil.DateTime{Date: d, Time: tm}
 	ts := time.Date(2016, 3, 20, 15, 04, 05, 0, time.UTC)
 	rat := big.NewRat(13, 10)
+	nrat := big.NewRat(-13, 10)
 	bigRat := big.NewRat(12345, 10e10)
 	rangeTimestamp1 := &RangeValue{
 		Start: time.Date(2016, 3, 20, 15, 04, 05, 0, time.UTC),
@@ -2208,6 +2209,13 @@ func initQueryParameterTestCases() {
 			[]Value{rat},
 			rat,
 		},
+		{
+			"NegativeBigRatParam",
+			"SELECT @val",
+			[]QueryParameter{{Name: "val", Value: nrat}},
+			[]Value{nrat},
+			nrat,
+		},
 		{
 			"BoolParam",
 			"SELECT @val",