Take you to master the three-tier architecture (recommended Collection)

Preface

Please pay attention to the following issues when reading this article ：

1. What is a three-tier architecture ？

2. Why use a three-tier architecture ？

3. What is the difference between the three layers and the two layers used in the past ？ What are its advantages ？

4. How to learn three-tier architecture well ？ How to apply the three-tier architecture ？ 

One 、 What is a three-tier architecture

        The three-tier architecture is to conform to “ High cohesion , Low coupling ” thought , Divide each function module into presentation layer （UI）、 Business logic

Series layer （BLL） and   Data access layer （DAL） Three layer architecture , Each layer uses interface to access each other , And through the implementation of the object model

Body class （Model） As the carrier of data transmission , The entity classes of different object models generally correspond to different tables of the database , Entity

The attribute of the class is consistent with the field name of the database table .

Function division table of each module ：

UI( The presentation layer ):	It mainly refers to the interface interacting with users . It is used to receive data input by users and display data needed by users after processing .
BLL:( Business logic layer ):	UI Layer and the DAL The bridge between layers . Implement business logic . The business logic specifically includes ： verification 、 Calculation 、 Business rules and so on .
DAL:( Data access layer ):	Dealing with databases . The main purpose is to increase data 、 Delete 、 Change 、 check . Submit the data stored in the database to the business layer , At the same time, the data processed by the business layer is saved to the database .（ Of course, these operations are based on UI Layer of . The user's needs are reflected in the interface （UI）,UI Reflect to BLL,BLL Reaction to DAL,DAL Data manipulation , Step back after operation , Until the user needs data feedback to the user ）

Three tier architecture operation flow chart ：

​

How to connect the functional modules in the three-tier architecture ？

        I want to mention Entity( Physical layer )： It doesn't belong to any of the three layers , But it is an essential layer . For a lot of data , Using variables as parameters is a little complicated , Because there are too many parameters , Easy to confuse . such as ： I want to pass the employee information to the lower level , The information includes ： Employee number 、 full name 、 Age 、 Gender 、 Wages ....... Using variables as parameters , Then there will be many parameters in our method , Most likely when used , Confuse parameter matching . Now , If you use entities as parameters , It will be very convenient , Don't consider the problem of parameter matching , You can use which attribute in the entity directly , Very convenient . This also improves efficiency .

Entity Role in three-tier architecture ：

1. Implement the in object-oriented thinking " encapsulation ";

2. Through the third floor , Transfer data between the three layers ;（ notes ： To be exact, the entity layer runs through the three layers , To connect the three layers ）

3. For beginners , It can be understood in this way ： Each data table corresponds to an entity , That is, the fields in each data table correspond to the attributes in the entity （ notes ： Of course , In fact, it's not .           Why? ？         1>) Maybe the entity we need does not exist in the entity corresponding to the data table         2>) We can put all fields in all data tables in one entity ）

4. Each layer （UI—>BLL—>DAL） Data transfer between （ A one-way ） Is passed by variables or entities as parameters , In this way, the connection between the three layers is constructed , Completed the implementation of the function .

（ Add ：3. in Why can we temporarily understand that each data table corresponds to an entity ？？

      The purpose of our system , Is to provide services for users , Users don't care how your system background works , Users only care about whether the software is easy to use , Whether the interface is in line with your own mind . The user interface is easy to add 、 Delete 、 Change 、 check , Then there should be corresponding additions in the database 、 Delete 、 Change 、 check , The specific operation object of adding, deleting, modifying and querying is the data in the database , To put it bluntly, the fields in the table . therefore , Treat each data table as an entity class , The attributes encapsulated by the entity class correspond to the fields in the table , In this case , When the entity runs through three layers , You can add, delete, modify and query data ）

  Between the three layers and the entity layer Dependency relationship ：

​

  

Two 、 Why use a three-tier architecture

        The purpose of the three-tier architecture is to “ High cohesion , Low coupling ”. A clearer division of developers , Focus more on the analysis of the core business logic of the application system 、 Design and development , Speed up the project , Improved development efficiency , It is conducive to the updating and maintenance of the project .

3、 ... and 、 The difference between three floors and two floors

Two layers of ：

（ When any place changes , Need to redevelop the whole system ." Multi-storey " On the first floor , Unclear division of labor and high coupling —— Difficult to adapt to changes in demand , Low maintainability 、 Low scalability ）

Three layers ：

（ At what level does the change take place , Just change the layer , There is no need to change the entire system . A clear hierarchy , A clear division of responsibilities , Low coupling between each layer —— Improved efficiency , Adapt to changing needs , High maintainability , High scalability ）

The advantages of three-tier architecture ：

1. The structure is clear 、 Low coupling

2. High maintainability , High scalability

3. It is conducive to synchronous development tasks , Easy to adapt to changing needs

Disadvantages of three-tier architecture ：

1. It reduces the performance of the system . This is self-evident . If you don't use a layered structure , Many businesses can visit the database directly , In order to obtain the corresponding data , Now it has to be done through the middle tier .

2. Sometimes it leads to cascading changes . This change is especially reflected in the top-down direction . If you need to add a function in the presentation layer , In order to ensure that its design conforms to the layered structure , You may need to add code in the corresponding business logic layer and data access layer

3. Increased code , Increased workload

---