In-depth exploration of MyBatis's one-to-many query configuration: flexible use of related queries

MyBatis is an excellent persistence layer framework, which not only simplifies database operations, but also provides powerful query functions. In actual development, multi-table related queries are often involved, and MyBatis can easily implement such related queries by configuring one-to-many queries. This article will introduce in detail the configuration method of MyBatis one-to-many query, and use specific code examples to show how to flexibly apply related queries.

1. The concept of one-to-many query

In a relational database, one-to-many means that one record in one table corresponds to multiple records in another table Record. For example, in the relationship between an order and order details, one order can correspond to multiple order details. In such a scenario, one-to-many query is required to obtain complete information.

2. Configure one-to-many query

1. Create entity class

First, we need to create the entity class of the corresponding relationship. Taking orders and order details as an example, create two entity classes, Order and OrderDetail, and add a List type attribute to the Order class.

public class Order {
    private int id;
    private String orderNumber;
    private List<OrderDetail> orderDetails;
    // 省略getter和setter方法
}

public class OrderDetail {
    private int id;
    private int orderId;
    private String productName;
    // 省略getter和setter方法
}

2. Create Mapper interface

Next, you need to create a Mapper interface and define a one-to-many query method.

public interface OrderMapper {
    Order selectOrderWithDetails(int id);
}

3. Write the Mapper mapping file

In the Mapper mapping file, configure the SQL statement for one-to-many query.

<mapper namespace="com.example.mapper.OrderMapper">
    <select id="selectOrderWithDetails" resultType="com.example.entity.Order">
        SELECT * FROM orders WHERE id = #{id};
        <collection property="orderDetails" ofType="com.example.entity.OrderDetail">
            SELECT * FROM order_details WHERE order_id = #{id};
        </collection>
    </select>
</mapper>

3. Use one-to-many query

In actual use, you can perform one-to-many query by calling the selectOrderWithDetails method of the OrderMapper interface.

Order order = orderMapper.selectOrderWithDetails(1);

The above are the detailed steps for configuring MyBatis one-to-many query. In this way, multi-table related queries can be easily implemented. In practical applications, query conditions and SQL statements can be adjusted according to specific needs, and the associated query function can be flexibly applied.

4. Summary

Through the introduction of this article, I believe readers will have a clearer understanding of the one-to-many query configuration of MyBatis. Reasonable application of related queries can improve the performance and efficiency of the system, and at the same time, it can also easily obtain related data information. I hope readers can use the guidance of this article to more flexibly use the related query function of MyBatis.

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