MyBatis 分步查询

最新推荐文章于 2025-03-20 10:15:49 发布

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最新推荐文章于 2025-03-20 10:15:49 发布 · 1.1k 阅读

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原文链接：https://my.oschina.net/lin546/blog/1633407

文章标签：

#java #数据库

本文详细介绍了如何在MyBatis中使用association和collection实现分步查询，并探讨了延迟加载的概念，通过配置延迟加载参数实现按需加载关联数据，减少不必要的数据库请求。

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1）association
使用association实现分步查询操作。

创建实体

Employee和Department

package org.mybatis.resultmap;

public class Employee {
    private Integer id;
    private String lastName;
    private String email;
    private String gender;
    private Department department;

    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    public String getGender() {
        return gender;
    }
    public void setGender(String gender) {
        this.gender = gender;
    }
    public Department getDepartment() {
        return department;
    }
    public void setDepartment(Department department) {
        this.department = department;
    }
    @Override
    public String toString() {
        return "Employee [id=" + id + ", lastName=" + lastName + ", email="
                + email + ", gender=" + gender + ", department=" + department
                + "]";
    }

}

package org.mybatis.resultmap;


public class Department {

    private Integer id;

    private String deptName;

    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getDeptName() {
        return deptName;
    }
    public void setDeptName(String deptName) {
        this.deptName = deptName;
    }

    public String toString() {
        return "Department [id=" + id + ", deptName=" + deptName + "]";
    }

}

创建接口类
DepartmentMapper和EmployeeMapper

package org.mybatis.resultmap;

public interface DepartmentMapper {

    public Department getDeptById(Integer id);

}

package org.mybatis.resultmap;

public interface EmployeeMapper {

    /**
     * 分步查询
     * @param id
     * @return
     */
    public Employee getEmpAndDeptByStep(Integer id);

}

创建映射配置文件
resultmapmapper.xml对应Employee和resultma