This paper briefly

Hello, students ！ This article mainly introduces HTTP Idempotency .HTTP The idempotence of a method means that a resource should have the same side effects when it is requested once or multiple times .

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One 、HTTP Request method

Two 、 Idempotency

2.1、HTTP GET Method

2.2、HTTP POST Method

2.3、HTTP PUT Method

2.4、HTTP PATCH Method

2.5、HTTP DELETE Method

3、 ... and 、 How to design high-quality products that conform to idempotence RESTful API

3.1、GET  vs POST

3.2、POST vs PUT

3.3、PUT vs PATCH

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One 、HTTP Request method

according to HTTP standard ,HTTP Requests can be made in a variety of ways .
GET POST HEAD OPTIONS PUT PATCH DELETE TRACE CONNECT.

index	method	description
1	GET	Request specific page information , And return the entity body
2	HEAD	Be similar to GET request , But there is no specific content in the response returned , For getting headers
3	POST	Submit data to the specified resource for processing request （ For example, submit a form or upload a file ）. Data is contained in the request body .POST Requests may lead to the creation of new resources and / Or modification of existing resources .
4	PUT	The data transmitted from the client to the server replaces the content of the specified document .（ Replace all ）
5	PATCH	The data transmitted from the client to the server replaces the content of the specified document .（ To partially replace ）
6	DELETE	Request the server to delete the specified page .
7	CONNECT	HTTP/1.1 The protocol is reserved for the proxy server that can change the connection to pipeline mode .
8	OPTIONS	Allow clients to view the performance of the server .
9	TRACE	Echo requests received by server , Mainly used for testing or diagnosis .

That's it HTTP A general introduction to the request method , Let's understand what is HTTP Idempotency of request method .

Two 、 Idempotency

HTTP Idempotent methods , It means that no matter calling this url How many times , There will be no different results HTTP Method . That is, no matter what you call 1 It's still a call 100 Time ,1000 Time , The results are the same （ The premise is that the data on the server side has not been changed manually . for instance , The data in your database has been manually changed , The results of those two calls must have changed ）.

Let's discuss GET POST PUT PATCH DELETE Idempotency .

GET /tickets # obtain ticket list
GET /tickets/12 # Look at a specific ticket
POST /tickets # Create a new one ticket
PUT /tickets/12 # to update ticket 12
PATCH /tickets/12 # to update ticket 12
DELETE /tickets/12 # Delete ticekt 12

2.1、HTTP GET Method

HTTP GET Method , Used to get resources , No matter how many interfaces are called , The results will not change , So it's idempotent .

GET /tickets # obtain ticket list
GET /tickets/12 # Look at a specific ticket

Just query the data , It won't affect the change of resources , So we think it's idempotent .
It is worth noting that , Idempotency refers to the action on the result rather than the resource itself . How do you understand that ？ for example , This HTTP GET Methods may get different returns each time , But it doesn't affect resources .
You may ask if this is the case ？ Of course . for example , We have an interface to get the current time , We should design it as

GET /service_time # Get the current time of the server

It will not affect the resource itself , Therefore, idempotency is satisfied .

2.2、HTTP POST Method

HTTP POST Method is a non idempotent method , Because it's called many times , Will generate new resources

POST /tickets # Create a new one ticket

Because it has an impact on the resources themselves , Every time you call, a new resource is generated , So it doesn't satisfy idempotency .

2.3、HTTP PUT Method

HTTP PUT Is the method idempotent ？ Let's see

PUT /tickets/12 # to update ticket 12

Because it directly replaces the data of the entity part with the resources of the server , We call it many times , It's only going to have an impact once , But with the same result HTTP Method , So it satisfies idempotency .

2.4、HTTP PATCH Method

HTTP PATCH Method is non idempotent .HTTP POST Methods and HTTP PUT The method may be easier to understand , however HTTP PATCH The method is only to update some resources , How is it non idempotent ?
because ,PATCH The entities provided need to be defined according to procedures or other agreements , After parsing, execute on the server , To modify the resources on the server . let me put it another way ,PATCH The request will execute a program , If you submit repeatedly , The program may be executed multiple times , There may be additional impact on the resources on the server , This explains why it is non idempotent .
Maybe you don't understand this yet . Let's take an example

PATCH /tickets/12 # to update ticket 12

here , Our server's processing of methods is , When a method is called , Update some fields , Take this ticket Add one to the recorded operation record , This time, , Does the resource of each call change , So it could be a non idempotent operation .

2.5、HTTP DELETE Method

HTTP DELETE Method to delete a resource , The resource will be deleted .

DELETE /tickets/12 # Delete ticekt 12

One call and multiple calls have the same impact on the resource , So it also satisfies idempotency .

3、 ... and 、 How to design high-quality products that conform to idempotence RESTful API

3.1、GET  vs POST

Maybe , You will think of an interview question .

HTTP Requested GET And POST What's the difference ？ You may answer ：GET Way through URL Submit data , The data is in URL Can be seen in ;POST The way , The data is placed in HTML HEADER The submission . however , We are from now on RESTful From the perspective of resources ,HTTP GET Method is idempotent , So it is suitable for query operation ,HTTP POST Method is non idempotent , Therefore, it is used to indicate the new operation .

however , There are exceptions. , Sometimes we may need to transform the query method into HTTP POST Method . such as , Super long （1k） Of GET URL Use POST To replace , because GET suffer URL Length limitation . although , It does not conform to idempotency , But it's a compromise .

3.2、POST vs PUT

about HTTP POST Methods and TTP PUT Method , Our general understanding is POST Represents creating a resource ,PUT Represents an update resource . Of course , This is the correct understanding .

however , actually , Both methods are used to create resources , The more essential difference is in idempotency .HTTP POST The method is non idempotent , So it is used to represent the creation of resources ,HTTP PUT Method is idempotent , Therefore, it means that updating resources is more appropriate .

3.3、PUT vs PATCH

here , You see, there will be another problem .HTTP PUT Methods and HTTP PATCH Method , Are used to describe update resources , What's the difference between them ？ Our general understanding is PUT Means to update all resources ,PATCH Indicates updating some resources . First , This is the first rule we follow . According to the description above ,PATCH Method is non idempotent , Therefore, we are designing our server side RESTful API When , Also need to consider . If , We want to make it clear to the caller that our resources are idempotent , My design tends to use HTTP PUT Method .