myBatis - foreach动态sql

forecah介绍

foreach的主要用在构建in条件中，它可以在SQL语句中进行迭代一个集合。foreach元素的属性主要有item，index，collection，open，separator，close。item表示集合中每一个元素进行迭代时的别名，index指定一个名字，用于表示在迭代过程中，每次迭代到的位置，open表示该语句以什么开始，separator表示在每次进行迭代之间以什么符号作为分隔符，close表示以什么结束，在使用foreach的时候最关键的也是最容易出错的就是collection属性，该属性是必须指定的，但是在不同情况下，该属性的值是不一样的。

foreach属性

代码实践

数据表:

采用Oracle的HR.Employees表

        实体:Employees

public class Employees {
    private Integer employeeId;
    private String firstName;
    private String lastName;
    private String email;
    private String phoneNumber;
    private Date hireDate;
    private String jobId;
    private BigDecimal salary;
    private BigDecimal commissionPct;
    private Integer managerId;
    private Short departmentId;
}  

映射文件:

    <!--List:forech中的collection属性类型是List,collection的值必须是:list,item的值可以随意,Dao接口中参数名字随意 -->
    <select id="getEmployeesListParams" resultType="Employees">
        select *
        from EMPLOYEES e
        where e.EMPLOYEE_ID in
        <foreach collection="list" item="employeeId" index="index"
            open="(" close=")" separator=",">
            #{employeeId}
        </foreach>
    </select>

    <!--Array:forech中的collection属性类型是array,collection的值必须是:list,item的值可以随意,Dao接口中参数名字随意 -->
    <select id="getEmployeesArrayParams" resultType="Employees">
        select *
        from EMPLOYEES e
        where e.EMPLOYEE_ID in
        <foreach collection="array" item="employeeId" index="index"
            open="(" close=")" separator=",">
            #{employeeId}
        </foreach>
    </select>

    <!--Map:不单单forech中的collection属性是map.key,其它所有属性都是map.key,比如下面的departmentId -->
    <select id="getEmployeesMapParams" resultType="Employees">
        select *
        from EMPLOYEES e
        <where>
            <if test="departmentId!=null and departmentId!=''">
                e.DEPARTMENT_ID=#{departmentId}
            </if>
            <if test="employeeIdsArray!=null and employeeIdsArray.length!=0">
                AND e.EMPLOYEE_ID in
                <foreach collection="employeeIdsArray" item="employeeId"
                    index="index" open="(" close=")" separator=",">
                    #{employeeId}
                </foreach>
            </if>
        </where>
    </select>

Mapper类:
public interface EmployeesMapper { 

    List<Employees> getEmployeesListParams(List<String> employeeIds);

    List<Employees> getEmployeesArrayParams(String[] employeeIds);

    List<Employees> getEmployeesMapParams(Map<String,Object> params);
}

测试方法(未贴完整代码):

    @Test 
    public void testGetEmployeesListParams() {
        List<String> employeeIds = Arrays.asList("100", "101", "200");
        List<Employees> result = employeesMapper
                .getEmployeesListParams(employeeIds);
        assertEquals(3, result.size());
    }

    @Test
    public void testGetEmployeesArrayParams() {
        String[] employeeIds = new String[] { "100", "200" };
        List<Employees> result = employeesMapper
                .getEmployeesArrayParams(employeeIds);
        assertEquals(2, result.size());
    }

    @Test
    public void testGetEmployeesMapParams() {
        String departmentId = "60";
        List<String> employeeIdsList = Arrays.asList("103", "104", "105");
        String[] employeeIdsArray = new String[] { "103", "104" };
        // 传入多个参数
        Map<String, Object> params = new HashMap<String, Object>();
        params.put("departmentId", departmentId);
        params.put("employeeIdsList", employeeIdsList);
        params.put("employeeIdsArray", employeeIdsArray);
        List<Employees> result = employeesMapper.getEmployeesMapParams(params);
        assertEquals(3, result.size());
    }

参考文档

https://blog.csdn.net/Small____Fish/article/details/8029030

https://blog.csdn.net/QH_JAVA/article/details/50754271