Use DB option in NewFailoverClusterClient (#3342)

sentinel.go

@@ -815,6 +815,22 @@ func NewFailoverClusterClient(failoverOpt *FailoverOptions) *ClusterClient {
 	}
 
 	opt := failoverOpt.clusterOptions()
+	if failoverOpt.DB != 0 {
+		onConnect := opt.OnConnect
+
+		opt.OnConnect = func(ctx context.Context, cn *Conn) error {
+			if err := cn.Select(ctx, failoverOpt.DB).Err(); err != nil {
+				return err
+			}
+
+			if onConnect != nil {
+				return onConnect(ctx, cn)
+			}
+
+			return nil
+		}
+	}
+
 	opt.ClusterSlots = func(ctx context.Context) ([]ClusterSlot, error) {
 		masterAddr, err := failover.MasterAddr(ctx)
 		if err != nil {

sentinel_test.go

@@ -200,6 +200,7 @@ var _ = Describe("NewFailoverClusterClient", func() {
 			SentinelAddrs: sentinelAddrs,
 
 			RouteRandomly: true,
+			DB:            1,
 		})
 		Expect(client.FlushDB(ctx).Err()).NotTo(HaveOccurred())
 
@@ -289,6 +290,20 @@ var _ = Describe("NewFailoverClusterClient", func() {
 		})
 	})
 
+	It("should sentinel cluster client db", func() {
+		err := client.ForEachShard(ctx, func(ctx context.Context, c *redis.Client) error {
+			return c.Ping(ctx).Err()
+		})
+		Expect(err).NotTo(HaveOccurred())
+
+		_ = client.ForEachShard(ctx, func(ctx context.Context, c *redis.Client) error {
+			clientInfo, err := c.ClientInfo(ctx).Result()
+			Expect(err).NotTo(HaveOccurred())
+			Expect(clientInfo.DB).To(Equal(1))
+			return nil
+		})
+	})
+
 	It("should sentinel cluster PROTO 3", func() {
 		_ = client.ForEachShard(ctx, func(ctx context.Context, c *redis.Client) error {
 			val, err := client.Do(ctx, "HELLO").Result()