Add NullDecimal to shopspring-numeric

The shopspring/decimal package provides a NullDecimal struct intended
for use with nullable SQL NUMERICs and numbers. It has Scanner and
Valuer implementations already, but adding it to this package allows
it to be used with the binary encoding as well.

The implementation is very straightforward, but the tests have been made
slightly more complicated. The previous version wasn't testing the
decimal.Decimal cases, and this change adds those as well as new
NullDecimal cases. I've added some logic to the test harness to catch
these as you need to use the Equals method to properly compare Decimals.

ext/shopspring-numeric/decimal.go

@@ -34,6 +34,12 @@ func (dst *Numeric) Set(src interface{}) error {
 	switch value := src.(type) {
 	case decimal.Decimal:
 		*dst = Numeric{Decimal: value, Status: pgtype.Present}
+	case decimal.NullDecimal:
+		if value.Valid {
+			*dst = Numeric{Decimal: value.Decimal, Status: pgtype.Present}
+		} else {
+			*dst = Numeric{Status: pgtype.Null}
+		}
 	case float32:
 		*dst = Numeric{Decimal: decimal.NewFromFloat(float64(value)), Status: pgtype.Present}
 	case float64:
@@ -113,6 +119,9 @@ func (src *Numeric) AssignTo(dst interface{}) error {
 		switch v := dst.(type) {
 		case *decimal.Decimal:
 			*v = src.Decimal
+		case *decimal.NullDecimal:
+			(*v).Valid = true
+			(*v).Decimal = src.Decimal
 		case *float32:
 			f, _ := src.Decimal.Float64()
 			*v = float32(f)
@@ -216,7 +225,11 @@ func (src *Numeric) AssignTo(dst interface{}) error {
 			return fmt.Errorf("unable to assign to %T", dst)
 		}
 	case pgtype.Null:
-		return pgtype.NullAssignTo(dst)
+		if v, ok := dst.(*decimal.NullDecimal); ok {
+			(*v).Valid = false
+		} else {
+			return pgtype.NullAssignTo(dst)
+		}
 	}
 
 	return nil

ext/shopspring-numeric/decimal_test.go

@@ -153,6 +153,9 @@ func TestNumericSet(t *testing.T) {
 		source interface{}
 		result *shopspring.Numeric
 	}{
+		{source: decimal.New(1, 0), result: &shopspring.Numeric{Decimal: mustParseDecimal(t, "1"), Status: pgtype.Present}},
+		{source: decimal.NullDecimal{Valid: true, Decimal: decimal.New(1, 0)}, result: &shopspring.Numeric{Decimal: mustParseDecimal(t, "1"), Status: pgtype.Present}},
+		{source: decimal.NullDecimal{Valid: false}, result: &shopspring.Numeric{Status: pgtype.Null}},
 		{source: float32(1), result: &shopspring.Numeric{Decimal: mustParseDecimal(t, "1"), Status: pgtype.Present}},
 		{source: float64(1), result: &shopspring.Numeric{Decimal: mustParseDecimal(t, "1"), Status: pgtype.Present}},
 		{source: int8(1), result: &shopspring.Numeric{Decimal: mustParseDecimal(t, "1"), Status: pgtype.Present}},
@@ -208,6 +211,8 @@ func TestNumericAssignTo(t *testing.T) {
 	var f64 float64
 	var pf32 *float32
 	var pf64 *float64
+	var d decimal.Decimal
+	var nd decimal.NullDecimal
 
 	simpleTests := []struct {
 		src      *shopspring.Numeric
@@ -231,16 +236,42 @@ func TestNumericAssignTo(t *testing.T) {
 		{src: &shopspring.Numeric{Decimal: mustParseDecimal(t, "42"), Status: pgtype.Present}, dst: &_i8, expected: _int8(42)},
 		{src: &shopspring.Numeric{Status: pgtype.Null}, dst: &pi8, expected: ((*int8)(nil))},
 		{src: &shopspring.Numeric{Status: pgtype.Null}, dst: &_pi8, expected: ((*_int8)(nil))},
+		{src: &shopspring.Numeric{Decimal: mustParseDecimal(t, "42"), Status: pgtype.Present}, dst: &d, expected: decimal.New(42, 0)},
+		{src: &shopspring.Numeric{Decimal: mustParseDecimal(t, "42000"), Status: pgtype.Present}, dst: &d, expected: decimal.New(42, 3)},
+		{src: &shopspring.Numeric{Decimal: mustParseDecimal(t, "0.042"), Status: pgtype.Present}, dst: &d, expected: decimal.New(42, -3)},
+		{src: &shopspring.Numeric{Decimal: mustParseDecimal(t, "42"), Status: pgtype.Present}, dst: &nd, expected: decimal.NullDecimal{Valid: true, Decimal: decimal.New(42, 0)}},
+		{src: &shopspring.Numeric{Status: pgtype.Null}, dst: &nd, expected: decimal.NullDecimal{Valid: false}},
 	}
 
 	for i, tt := range simpleTests {
+		// Zero out the destination variable
+		reflect.ValueOf(tt.dst).Elem().Set(reflect.Zero(reflect.TypeOf(tt.dst).Elem()))
+
 		err := tt.src.AssignTo(tt.dst)
 		if err != nil {
 			t.Errorf("%d: %v", i, err)
 		}
 
-		if dst := reflect.ValueOf(tt.dst).Elem().Interface(); dst != tt.expected {
+		// Need to specially handle Decimal or NullDecimal methods so we can use their Equal method. Without this
-			t.Errorf("%d: expected %v to assign %v, but result was %v", i, tt.src, tt.expected, dst)
+		// we end up checking reference equality on the *big.Int they contain.
+		switch dst := tt.dst.(type) {
+		case *decimal.Decimal:
+			if !dst.Equal(tt.expected.(decimal.Decimal)) {
+				t.Errorf("%d: expected %v to assign %v, but result was %v", i, tt.src, tt.expected, d)
+			}
+		case *decimal.NullDecimal:
+			expected := tt.expected.(decimal.NullDecimal)
+
+			if dst.Valid != expected.Valid {
+				t.Errorf("%d: expected %v to assign NullDecimal.Valid = %v, but result was NullDecimal.Valid = %v", i, tt.src, expected.Valid, dst.Valid)
+			}
+			if !dst.Decimal.Equal(expected.Decimal) {
+				t.Errorf("%d: expected %v to assign NullDecimal.Decimal = %v, but result was NullDecimal.Decimal = %v", i, tt.src, expected.Decimal, dst.Decimal)
+			}
+		default:
+			if dst := reflect.ValueOf(tt.dst).Elem().Interface(); dst != tt.expected {
+				t.Errorf("%d: expected %v to assign %v, but result was %v", i, tt.src, tt.expected, dst)
+			}
 		}
 	}