Implement SingleOrNil (#21)

Author: dfava

querysql/querysql.go

@@ -6,6 +6,7 @@ package querysql
 import (
 	"context"
 	"database/sql"
+	"errors"
 	"fmt"
 	"io"
 	"strings"
@@ -312,6 +313,14 @@ func MustSingle[T any](ctx context.Context, querier CtxQuerier, qry string, args
 	return must(Single[T](ctx, querier, qry, args...))
 }
 
+func SingleOrNil[T any](ctx context.Context, querier CtxQuerier, qry string, args ...any) (*T, error) {
+	v, err := Single[T](ctx, querier, qry, args...)
+	if err != nil && errors.Is(err, sql.ErrNoRows) {
+		return nil, nil
+	}
+	return &v, err
+}
+
 func Slice[T any](ctx context.Context, querier CtxQuerier, qry string, args ...any) ([]T, error) {
 	return NextResult(New(ctx, querier, qry, args...).EnsureDoneAfterNext(), SliceOf[T])
 }

querysql/querysql_test.go

@@ -730,3 +730,24 @@ func Test_TypeThatImplementsScan(t *testing.T) {
 	_, err := Single[MyType](ctx, sqldb, qry, "world")
 	assert.NoError(t, err)
 }
+
+func Test_SingleOrNil(t *testing.T) {
+	// No easy way to do this as a table driven test because
+	// we are calling funcs (Single and SingleOrNil) with different signatures
+	ctx := context.Background()
+
+	// query returns no result set; gives error when queried with Single
+	_, err := Single[int](ctx, sqldb, `select 1 where 0 = 1;`, "world")
+	require.Error(t, err)
+	require.True(t, errors.Is(err, sql.ErrNoRows))
+
+	// query returns no result set; gives no error when queried with SingleOrNil
+	vptr, err := SingleOrNil[int](ctx, sqldb, `select 1 where 0 = 1;`, "world")
+	require.NoError(t, err)
+	require.Nil(t, vptr)
+
+	// query returns an error; gives error when queried with SingleOrNil
+	vptr, err = SingleOrNil[int](ctx, sqldb, `throw 55002, 'Here is an error', 1;`, "world")
+	require.Error(t, err)
+	require.False(t, errors.Is(err, sql.ErrNoRows))
+}