What is the DAO design pattern and what is the DAO factory pattern?

Introduction to Design Patterns.

The full name of DAO is Data Access Object, database access object, the main function is used for data operations, and it belongs to the operation of the data layer in the standard development architecture of the program.

2.Enterprise hierarchical architecture.

Client: Because the BS development architecture is now adopted, it is generally accessed using a browser.

Display Layer: Use JSP Servlet to display page effects.

Business Layer: (Business Object): Combines multiple atomic DAO operations into a complete business logic.

Data Layer (DAO): Provides multiple atomic DAO operations, such as adding, modifying, deleting, etc., all of which are atomic operations.

In the whole DAO, the composition is actually based on the interface as the operation standard, that is, the client relies on the interface implemented by the DAO to operate, and the server needs to implement the interface specifically. A DAO consists of the following parts:

1》 databaseconnection: a class that is responsible for opening and closing databases.

2》VO: It is mainly composed of attributes, setters, and getter methods, and the attributes in the VO class correspond to the fields in the table, and the objects of each VO class represent every record in the table;

3》DAO: The interface that mainly defines operations, defines a series of atomic operations of the database, such as: adding, modifying, deleting, querying by ID, etc.;

4》IMPL: The real implementation class of the DAO interface, which completes specific database operations, but is not responsible for the opening and closing of the database;

5》Proxy :** implements the class, which mainly completes the opening and closing of the database, and calls the operation of the real implementation class object;

6》factory: factory class, get a DAO instantiation object through the factory class.

Encapsulating the basic CRUD operations of an object into a DAO is the design pattern.

Must be decoupled from other layers, you can use the ** mode, if the upper layer has a number of different classes to call the dao layer of multiple different objects, you can consider using the mediator mode, otherwise the call relationship is too complex will make the ** maintenance very troublesome.

The DAO layer is the logical layer that deals with the database, which encapsulates some basic methods of database operations.

The service layer is the business layer, and it is likely that you need to add a log to the log table when you register a user, so you can implement the service in the service and add transactions to the business. The benefits speak for themselves. If you're using UserDAO LogDao continuously on your C-layer, that's in case something goes wrong.

It may cause the user to be added and the log not to be added.

The client sends a request to the server.

The server sends the request information to the servlet

The servlet generates the response and passes it to the server.

The response content is dynamically generated and is typically dependent on the client's request.

The server returns the response to the client.

Give specific entities to subclasses.

Specific entity DAOs are specified, but no who they are.

Only database-related operations are processed.

No interface is provided at the service layer.

General Province**.

Easy to maintain. Generally, it is a unified save (new and updated), delete, get(id), getall(), etc., of course, inheriting the same class, you can also do more.

public class userdaoimpl extends genericdaoimplimplements iuserdao

Write a lot less**, increase type control automatic transformation, universal.

GetBy like the one above, genericdaoimpl has been implemented, and the subclasses don't need to be written anymore and don't need to convert types.

The DAO is only responsible for accessing the data, which is the model in the MVC

Layer. But what data is accessed, in what order, and what result is returned, this is what the service layer does, corresponding to the controller layer in MVC.

The DAO layer generally only adds, deletes, modifies and checks, operates the database, and has nothing else**, the service layer is the business logic layer, for example, user registration, the registration information is saved to the database, and the user information is designed to the business logic in the service layer, and it is necessary to judge whether there are duplicate usernames in the database before saving, if not, after encrypting the password, it is passed into the dao, and the dao is inserted in, so the **do not mix the business logic**, Receive the processed data from the service and save it. In this way, the layers are separated, it is easier to maintain, and the methods of the DAO layer are also easy to reuse.

DAO is responsible for adding, deleting, modifying, and querying databases, and is responsible for single-table operations.

Service calls DAOs to implement business logic operations, which involves multi-table operations, and sometimes a business logic operation calls methods from multiple DAOs.

Therefore, the transaction is controlled in the service layer.

For example: UserDao

deptdao

deptservice}

The DAO is the data access layer, and the service is the business logic layer, which must be separated to reduce the degree of cohesion and facilitate maintenance.

If you have to delete and check it, you can actually write it in one.,You don't even need to divide the layers.,The main reason for layering is to clarify your thoughts.,You can also expand it in the future! Developing good layering habits is good for future development! I'm also a beginner, so if I don't use it correctly, I just listen to what I say.

The DAO layer is the data layer and the control layer, so it is logically clearer to separate.

The DAO is only responsible for accessing the data, that is, the model layer in the MVC, but what data is accessed, in what order, and what result is returned, which is what the Service layer does, corresponding to the controller layer in MVC.