feat: support structs in queries (#282)

cloud.google.com/go/spanner supports passing structs as arguments to
queries.

Fixes #281

driver.go

@@ -20,6 +20,7 @@ import (
 	"database/sql/driver"
 	"fmt"
 	"math/big"
+	"reflect"
 	"regexp"
 	"strconv"
 	"strings"
@@ -36,6 +37,8 @@ import (
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/reflect/protoreflect"
 )
 
 const userAgent = "go-sql-spanner/1.0.2"
@@ -748,6 +751,10 @@ func (c *conn) IsValid() bool {
 func checkIsValidType(v driver.Value) bool {
 	switch v.(type) {
 	default:
+		// google-cloud-go/spanner knows how to deal with these
+		if isStructOrArrayOfStructValue(v) || isAnArrayOfProtoColumn(v) {
+			return true
+		}
 		return false
 	case nil:
 	case sql.NullInt64:
@@ -1052,3 +1059,32 @@ func (c *conn) createPartitionedDmlQueryOptions() spanner.QueryOptions {
 	defer func() { c.excludeTxnFromChangeStreams = false }()
 	return spanner.QueryOptions{ExcludeTxnFromChangeStreams: c.excludeTxnFromChangeStreams}
 }
+
+/* The following is the same implementation as in google-cloud-go/spanner */
+
+func isStructOrArrayOfStructValue(v interface{}) bool {
+	typ := reflect.TypeOf(v)
+	if typ.Kind() == reflect.Slice {
+		typ = typ.Elem()
+	}
+	if typ.Kind() == reflect.Ptr {
+		typ = typ.Elem()
+	}
+	return typ.Kind() == reflect.Struct
+}
+
+func isAnArrayOfProtoColumn(v interface{}) bool {
+	typ := reflect.TypeOf(v)
+	if typ.Kind() == reflect.Ptr {
+		typ = typ.Elem()
+	}
+	if typ.Kind() == reflect.Slice {
+		typ = typ.Elem()
+	}
+	return typ.Implements(protoMsgReflectType) || typ.Implements(protoEnumReflectType)
+}
+
+var (
+	protoMsgReflectType  = reflect.TypeOf((*proto.Message)(nil)).Elem()
+	protoEnumReflectType = reflect.TypeOf((*protoreflect.Enum)(nil)).Elem()
+)

examples/struct-types/main.go

@@ -0,0 +1,71 @@
+// Copyright 2024 Google LLC
+//
+// Licensed 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
+//
+//     https://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.
+
+package main
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	_ "github.com/googleapis/go-sql-spanner"
+	"github.com/googleapis/go-sql-spanner/examples"
+)
+
+// Example for executing a query with struct arguments described in:
+//
+// * https://cloud.google.com/spanner/docs/structs
+// * https://pkg.go.dev/cloud.google.com/go/spanner#hdr-Structs
+func structTypes(projectId, instanceId, databaseId string) error {
+	ctx := context.Background()
+	db, err := sql.Open("spanner", fmt.Sprintf("projects/%s/instances/%s/databases/%s", projectId, instanceId, databaseId))
+	if err != nil {
+		return fmt.Errorf("failed to open database connection: %v\n", err)
+	}
+	defer db.Close()
+
+	type Entry struct {
+		ID   int64
+		Name string
+	}
+
+	entries := []Entry{
+		{ID: 0, Name: "Hello"},
+		{ID: 1, Name: "World"},
+	}
+
+	rows, err := db.QueryContext(ctx, "SELECT id, name FROM UNNEST(@entries)", entries)
+	if err != nil {
+		return fmt.Errorf("failed to execute query: %v", err)
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var id int64
+		var name string
+
+		if err := rows.Scan(&id, &name); err != nil {
+			return fmt.Errorf("failed to scan row values: %v", err)
+		}
+		fmt.Printf("%v %v\n", id, name)
+	}
+	if err := rows.Err(); err != nil {
+		return fmt.Errorf("failed to execute query: %v", err)
+	}
+	return nil
+}
+
+func main() {
+	examples.RunSampleOnEmulator(structTypes)
+}