High quality resource sharing

background

I summed up a few years ago DDD Some landing experience of tactical design It's landing DDD(5)- Tactical design , and A heated discussion about aggregate roots There have been some new landing experiences in the past two years , Look back and find out , The original understanding of these concepts is still not in-depth , This article reinterprets .

There are some points that I didn't understand well before

1. Each module of tactical design is a collaborative relationship
2. What are problem space problems , What is the boundary of the scheme space problem is not clearly divided .
3. The difference between entity and aggregation root is not well understood , Entity and aggregation root modeling methods are wrong .

The above questions will be explained clearly below .

Tactical design disassembly

DDD The tactical design of is to design the domain model of a certain sub domain and code landing . Field events 、 Domain object 、 Aggregate root 、 Entity 、 The value object 、 Field service 、 factory 、 These concepts such as resource pool belong to this category .

The author reassembles these concepts in layers , As shown in the figure below .

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First, divide the whole into two parts , Problem space and solution space .

1. Problem space is domain modeling . It is a description of business problems , And how we abstract these problems . These are needed in business 、 product 、 Development must be agreed , It has nothing to do with the specific technical scheme .
2. Solution space is how to use technical means to solve problems , It is related to the realization of specific technology .

Problem space is domain modeling , Through entities 、 The value object 、 Field service 、 Domain events .

1. Entity and value objects are model objects , Entity is the top priority , Including core model data 、 Behavior 、 state . The reason to distinguish between entities and value objects , To reduce complexity , Because the value object is a constant object , It doesn't take much energy .
   Note that an object is a value object in a field , In another field, it may be an entity , So get out of the domain context , Say an object is a value object , It must be wrong , For example, we often say that the address is a value object , Must this be right ？
2. Domain events are events generated by entities
3. Domain services include some logical calculations , And business strategy . For example, business decision logic 、 Business process, etc .

Solution space is how to solve problems , Realize the mapping between domain model and code . Realize the consistency between design and implementation . Mainly through factories , polymerization , Resource base to express .

1. Aggregation is about entities 、 Encapsulation of value objects . All access to domain objects outside the domain is based on aggregation . For example, the infrastructure layer operates aggregation to save data . Other domains reference aggregate object data .
   The design of aggregation generally revolves around technology , For example, aggregate object transaction .
2. factory , Complex object creation factory class
3. The repository , Operations on aggregation .

From the perspective of the author's practice , to ground DDD In the process , Problem space is more important than solution space , The benefits are greater . Because usually some of the code we roast about is poorly written , Anemia model . It's not because it's useless DDD, But the problem space is not well defined , Have no deep understanding of business , This leads to insufficient model abstraction .

How to model

Why modeling

Usually landing in a certain sub domain DDD, We will analyze according to business -》 Use case analysis -》 Domain modeling ( Problem space ) -》 Technical landing （ Solution space ） These steps operate . But in fact, even if we don't land in the code DDD, Just use the front 3 Maintaining a domain model in a sub domain can also bring a lot of benefits , Including but not limited to

1. Unify the cognition of each role of the business group , Business 、 product 、 Develop everyone's understanding of the same concept is consistent .
2. Guide the splitting of development work .

For example, there is a bloody lesson in Taobao , So far, this historical debt cannot be repaired . Early in Taobao shop . A seller can only open one store . Sellers and stores are objects in two fields , The relationship is 1:1. The service of the store is 1:1 The relationship between , The services provided externally are well founded sellerId Get store information , So other callers unconsciously quoted the seller directly id, In this way, you can also get to the store . Lead to shopId Is equivalent to sellerID. This misquotation occurred in thousands of places , Finally, the subsequent need to support a seller to open multiple stores cannot support . Only through other trick How to achieve .

As previously introduced CRM field To explain .
Omit business analysis , Get the use case directly .

Use case analysis

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List all use cases by user role , Used to derive the model 、 And the relationship between models . The domain model is established , You need to go through the listed use cases , Make sure that all use cases work . Only a complete set of use cases can derive the correct model , So when there is a change , First adjust the use case set , Then modify the domain model

modeling

Domain modeling is to define model objects , And the relationship between model objects . Modeling in two steps , The first step is to find the model object through nouns . The second step is to pass the verb 、 Adjective analysis object relevance

Noun

Usually, the nouns in the subject and object that appear repeatedly are the model objects , For example, marketing personnel create an activity , An activity is a model object . Of course, nouns appearing in attributives may also be model objects .

1. The definition of nouns must be clear . for instance crm There is a common term in the field called business opportunity . But your product manager is not familiar with crm field , Created a new word , Then you should correct him as soon as possible .

2. The meaning of a noun is semantically unique within the bounded context , The concept is not necessarily the same in different contexts . For example, activities created by marketing personnel , And the activities created during marketing are not necessarily .

Verb 、 Activities

1 One marketing person can create multiple activities , Therefore, the relationship between marketing personnel and activities is 1 For more than . The two exist independently , General relationship .

In order to simplify the description , Only market activities are listed 、 clue 、 Customer 、 Business opportunity these fields . user 、 role 、 jurisdiction 、 Data analysis these fields are ignored first .

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Output

In the process of derivation , We derive it from the bottom up , Finally, we present the results in the following way

1. Domain terms
   Marketing activities : Marketing personnel in order to show the company's image 、 Promote the company's products , Activities held to get clues . Multiple clues can be created in one activity .

clue : Salespeople explore potential customers based on clues , Multiple leads turn into one customer . Clues can be generated by a market activity , Or other channels .

Customer ： Users who are interested in buying the company's products , Salesperson can follow up with customers , Transform sales opportunities .

Opportunities ： Higher quality clues , Have the opportunity to sign the bill . You can get , It can also be obtained through other channels

2. Domain model
   Pictured above
3. Main fields state transition .
   Because the complex domain object life cycle and some cross domain object interactions cannot be expressed in the domain model diagram , So we need to express with the help of additional graphs .

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