What methods should service define?

One 、 background

Recently during code review , I will find that some new students in school will take some steps as Service Methods , stay Facade Layer arranges these steps to complete a complete function . This is obviously not normal .

Facade Layer is usually used as the entry of front-end or other service calls , Mainly responsible for parameter verification 、 Parameters required to construct the underlying service 、 Result conversion, etc .

A single business function should not be split into Service in , stay Facade These methods are arranged in , Finally complete a business function .

Facade As a facade , There should be no business logic in itself , Business logic should be placed in Service layer .Service Each method of should be able to complete a relatively complete business intention independently , Instead of providing multiple steps of a function , Let the outside assemble .

Two 、 Definition

Service The service in should have “ Business atomicity ”, This atomicity is not exactly the same as that of a database .
The so-called business atomicity refers to the ability to completely realize a certain business , Not a sub step of a business .

3、 ... and 、 analogy

This is like what many places offer “ Run once at most ” The policy of , Complete a business , Just run once ; There is no need to complete only one step of a certain intention at a time .

It's like buying a cup of coffee in the self-service coffee machine , You just need to choose the right type , Just pay . The production of coffee may include heating water 、 Add coffee powder 、 Add milk 、 Mixing and other steps , You should not know or participate in every process . Coffee service should be complete , Not every step requires you to press a button to arrange .

Just like the currency exchange service , You go to the exchange window to exchange RMB into baht , The general service is complete , Generally, they give RMB to them , They can directly give you the corresponding amount of baht .
You don't need to check the exchange rate yourself , Calculate the amount you can exchange , Go to their counter and take out the money by yourself , Count by yourself , Then say to yourself “ looking forward to your next visit ”.

The facade is equivalent to the public comment , Users can see the location of the target store here 、 Switching time and other information .


You can even comment on the public 、 Meituan orders , However, the target store is still required to provide corresponding catering services .

Reference resources 《 Clean code 》 Chapter six A case in the object and data structure section ：

encapsulation 1：

public interface Vehicle{
    
   double getFuelTankCapacityInGallons();

   double getGallonsOfGasoline();
}

encapsulation 2：

public interface Vehicle{
    
   double getPercentFuelRemaining();
}

The second interface definition method is better , We should not expose data details , Data should be expressed in an abstract way , Think a little about the defined interface .

This mainly includes several aspects ：
1 Design interface principles try to hide complexity （ The principle of least knowledge ）
2 Service The method provided by the layer should express the complete business intention （ If I want to check the percentage of fuel tank left ; Instead of providing two interfaces , One is to query the total quantity , Then check the current quantity and calculate it by yourself ）, Not a step .