Application of design patterns in MyBatis framework

The MyBatis framework widely applies design patterns, including: factory mode: creates SqlSessionFactory objects, manages database connections and queries; proxy mode: implements delayed loading and lazy loading, and improves performance. Appearance mode: encapsulates database access and simplifies code maintenance. Among them, one-to-many relationship mapping can be implemented through the User and Order classes, Mapper interface and Mapper XML configuration, using lazy loading and nested resultMap to optimize performance.

Application of design patterns in the MyBatis framework

Introduction
MyBatis is a Java-based A persistence layer framework for simplifying database interactions. It uses design patterns to promote scalability, flexibility, and maintainability. This article will explore common design patterns in MyBatis and their practical applications.

Factory Pattern
Factory pattern creates an instance of an object without specifying a specific class. MyBatis uses this pattern to create SqlSessionFactory, which is responsible for creating SqlSession, which is used to manage database connections and queries.

Proxy mode
Proxy mode creates a proxy object between the target object and the client. MyBatis uses this pattern to implement lazy and lazy loading, which improves performance because it only loads associated objects when needed.

Appearance mode
The appearance mode encapsulates a complex subsystem into a simple interface, so that the client only needs to call the interface to complete the operation. MyBatis uses this pattern to encapsulate access to the database, making the code clearer and easier to maintain.

Practical case: Implementing one-to-many relationship mapping

// POJO 类
class User {
    private List<Order> orders;
    // ...
}

class Order {
    private User user;
    // ...
}

// Mapper 接口
interface UserMapper {
    User selectUserWithOrders(int userId);
}

// Mapper XML 配置
<select id="selectUserWithOrders" resultType="com.example.User">
    SELECT * FROM users WHERE id = #{userId}
    <resultMap id="userWithOrdersResultMap" type="com.example.User">
        <collection property="orders" column="id" 
                    select="com.example.OrderMapper.selectOrderByUserId" 
                    ofType="com.example.Order" />
    </resultMap>
</select>

In this case, User and Order POJO classes Use one-to-many relationship mapping. The UserMapper interface defines the selectUserWithOrders method, which returns the user's order list through the User.orders property. The Mapper XML configuration uses nested resultMap to configure one-to-many mapping, and uses the collection element to specify lazy-loaded correlation queries.

Conclusion
The MyBatis framework provides a set of powerful functions through the application of design patterns that can greatly improve the efficiency, flexibility and maintainability of database interactions. Understanding and applying these patterns is critical to using MyBatis effectively.

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