Command mode and design of go redis command

itread01 2021-01-22 13:59:39
command mode design redis command

[TOC]#### One 、 What is an order (Command) Pattern command pattern is a kind of behavioral design pattern , The purpose is to encapsulate a request as an object , So that you can parameterize customers with different requests . Compared to another way of combining each command with the object calling the command to form a proprietary class , The advantage of command mode is that it decouples the object calling the operation from the object knowing how to implement the operation , Adding new commands does not require modifying existing classes . The structure of the command mode is as follows :![command]( The participants are :1.Invoker The requester asks the command to execute the request , The caller of the order 2.Command Interface 3.ConcreteCommand Specific interfaces 4.Receiver The actual implementer of the operation related to the receiver's command 5.Client Collaborative process :1.Client Build a ConcreteCommand Object and specify its Receiver thing 2. some Invoker The object stores the ConcreteCommand thing 3. The Invoker By calling Command Of objects Excute Operation to submit a request . If the command is revocable ,ConcreteCommand It's just executing Excute Save the current state before operation to cancel the command 4.ConcreteCommand The object calls its Receiver To perform the request #### Two 、go-redis command Related code ```// commands.go// Invoker Requester interface type Cmdable interface { Pipeline() Pipeliner Pipelined(ctx context.Context, fn func(Pipeliner) error) ([]Cmder, error) TxPipelined(ctx context.Context, fn func(Pipeliner) error) ([]Cmder, error) TxPipeline() Pipeliner Command(ctx context.Context) *CommandsInfoCmd ClientGetName(ctx context.Context) *StringCmd // ... // And all Redis Command related methods }// cmdable Achieved Cmdable Interface type cmdable func(ctx context.Context, cmd Cmder) error func (c cmdable) Echo(ctx context.Context, message interface{}) *StringCmd { cmd := NewStringCmd(ctx, "echo", message) _ = c(ctx, cmd) return cmd}``` What is worth mentioning here is cmdable Is a function type ,func(ctx context.Context, cmd Cmder) error And every one of them cmdable There will be in every way _ = c(ctx, cmd), That's how to call cmd I haven't written it clearly yet. Let's look back redis.go, You'll find this piece of code ```type Client struct { *baseClient cmdable hooks ctx context.Context}func NewClient(opt *Options) *Client { opt.init() c := Client{ baseClient: newBaseClient(opt, newConnPool(opt)), ctx: context.Background(), } c.cmdable = c.Process // scribing return &c}```c.cmdable = c.Process This line specifies how the request calls Command The in ctrl+ Left click to track several layers , Will be in redis.go Find the specific process of the call in ```// redis.go func (c *baseClient) process(ctx context.Context, cmd Cmder) error { ...... err := cn.WithWriter(ctx, c.opt.WriteTimeout, func(wr *proto.Writer) error { eturn writeCmd(wr, cmd) }) err = cn.WithReader(ctx, c.cmdTimeout(cmd), cmd.readReply) ...... ``` And then go to Command, This is clearer , All in command.go in ```// command.go// Command Interface type Cmder interface { Name() string FullName() string Args() []interface{} String() string stringArg(int) string firstKeyPos() int8 setFirstKeyPos(int8) readTimeout() *time.Duration readReply(rd *proto.Reader) error SetErr(error) Err() error}// There are many more Cmder The concrete realization of , Part of the code for one of the implementations is as follows type XPendingExtCmd struct { baseCmd val []XPendingExt}func (cmd *XPendingExtCmd) Val() []XPendingExt { return cmd.val}``` I don't see it here Receiver, Because of every Cmder All the functions are realized by themselves , There's no need for additional recipient objects at all .#### 3、 ... and 、 Summary sometimes you have to submit a request to something , But do not know any information about the requested operation or the recipient of the request . You can use command mode at this time , By turning the request itself into an object, the toolbox object can make a request to an unspecified application object

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