myBatis - foreach动态sql

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概述

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:

<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>

    
    <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>

    
    <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());

    }