Add missing error checks and support for MGET in Scan()

Author: knadh

command.go

@@ -375,9 +375,21 @@ func (cmd *SliceCmd) String() string {
 // Scan scans the results from the map into a destination struct. The map keys
 // are matched in the Redis struct fields by the `redis:"field"` tag.
 func (cmd *SliceCmd) Scan(dest interface{}) error {
-	// Pass the list of keys and values. Skip the first to args (command, key),
-	// eg: HMGET map.
-	return hscan.Scan(cmd.args[2:], cmd.val, dest)
+	if cmd.err != nil {
+		return cmd.err
+	}
+
+	// Pass the list of keys and values.
+	// Skip the first two args for: HMGET key
+	var args []interface{}
+	if cmd.args[0] == "hmget" {
+		args = cmd.args[2:]
+	} else {
+		// Otherwise, it's: MGET field field ...
+		args = cmd.args[1:]
+	}
+
+	return hscan.Scan(args, cmd.val, dest)
 }
 
 func (cmd *SliceCmd) readReply(rd *proto.Reader) error {
@@ -929,6 +941,10 @@ func (cmd *StringStringMapCmd) String() string {
 // Scan scans the results from the map into a destination struct. The map keys
 // are matched in the Redis struct fields by the `redis:"field"` tag.
 func (cmd *StringStringMapCmd) Scan(dest interface{}) error {
+	if cmd.err != nil {
+		return cmd.err
+	}
+
 	// Pass the list of keys and values. Skip the first to args (command, key),
 	// eg: HGETALL map.
 	var (

example_test.go

@@ -310,6 +310,39 @@ func ExampleStringStringMapCmd_Scan() {
 	// Output: {hello 123 true}
 }
 
+// ExampleSliceCmd_Scan shows how to scan the results of a multi key fetch
+// into a struct.
+func ExampleSliceCmd_Scan() {
+	rdb.FlushDB(ctx)
+	err := rdb.MSet(ctx,
+		"name", "hello",
+		"count", 123,
+		"correct", true).Err()
+	if err != nil {
+		panic(err)
+	}
+
+	res := rdb.MGet(ctx, "name", "count", "empty", "correct")
+	if res.Err() != nil {
+		panic(err)
+	}
+
+	type data struct {
+		Name    string `redis:"name"`
+		Count   int    `redis:"count"`
+		Correct bool   `redis:"correct"`
+	}
+
+	// Scan the results into the struct.
+	var d data
+	if err := res.Scan(&d); err != nil {
+		panic(err)
+	}
+
+	fmt.Println(d)
+	// Output: {hello 123 true}
+}
+
 func ExampleClient_Pipelined() {
 	var incr *redis.IntCmd
 	_, err := rdb.Pipelined(ctx, func(pipe redis.Pipeliner) error {