Domain Driven Design

One 、 Domain-driven design

As mentioned earlier , Domain driven design is actually business driven design , It's just that the business is more straightforward , The domain is more abstract . Domain-driven design , In fact, it is to refine the actual business scenario , Then through experts and design in this business field 、 Developers use a common language , Discover and generate domain concepts , Abstract the domain model that reflects the real world . This is often referred to as domain oriented thinking .
There are two major steps in Domain Driven Design ：
1、 Abstract the domain model from specific business
2、 Driven by domain model to complete software code design and development .
In fact, Domain Driven Design didn't produce much water flowers at the beginning , At least at home , Just with the rapid development of mobile Internet in recent years , People see some of the mysteries , Only gradually pay attention to it .

Two 、 The idea and core of Domain Driven Design

The idea of domain driven design is to have domain thinking , We should be able to use the idea of the field to guide the transformation of the entire business requirements to software design . let me put it another way , Have a higher level of understanding of the business , Instead of just understanding the business , The so-called higher-level cognition , Is the abstract . therefore , The core of domain driven design is MDD, That is, model design . A good model designed in a common language , It can better let people in all links of the whole program actively participate , And can better remove some “ noise ”. therefore , The domain layer is the essence of the model .
So what is the domain ？ We can understand the boundary of molding business , The overall context of granular business . So the depth of understanding of the field , Determines the advantages and disadvantages of domain driven design , It also determines the elasticity and scalability of model generation . This is also the most common principle and means to separate domains and form domain hierarchies in domain design .

3、 ... and 、 Application of Domain Driven Design

Domain driven design can be divided into two parts from two higher levels ：
1、DDD Strategic level design
The strategic focus is to decompose and control the problem space and the two directions of the reconciliation space .
2、 Design at the tactical level
Tactics are designed in the restricted environmental context and boundary within the specific subspace limited by the strategy .
The design of strategy and tactics is dialectical , Don't say much about this .

When designing a domain model , Generally, there are the following steps ：
a、 Create a preliminary domain model based on actual requirements , And according to specific fields and related relationships , Describe it in common language ;
b、 Classify the whole application layer according to actual functions , And further divide the application layer and domain layer ;
b、 Segment domain model , Divide entities , Values and objects , And domain services ;
f、 Analyze the relationship in the field , Remove noise ;
e、 Find the boundary to aggregate and determine the aggregation （AGGREGATE） root , This needs continuous practice and summary ;
f、 Determine the design allocation and interface control of aggregation root and warehouse ;
g、 Check the adaptability between the scene and the domain model of the design and constantly improve ;
h、 Consider how domain entities or values are built （ Directly or using the factory ）;
i、 Constantly iteratively reconstruct the domain model , Constantly improve and modify the domain model .

Four 、 summary

You can see it here , In fact, domain driven design is the abstraction of specific business scenarios , It is the abstraction under the continuous subdivision of different businesses . In the present , I want to build a middle office to handle all businesses , It looks beautiful , In fact, it is contrary to reality . Maybe , At some point in the future , With the evolution of technology and the improvement of ideological ability , It is possible to achieve this grand goal . But that is another matter .
Tell the present story , Say business now , Seeking truth from facts .