MyBatis参数传入集合之foreach动态sql

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，主要有一下3种情况： 

如果传入的是单参数且参数类型是一个List的时候，collection属性值为list .
如果传入的是单参数且参数类型是一个array数组的时候，collection的属性值为array .
如果传入的参数是多个的时候，我们就需要把它们封装成一个Map了，当然单参数也可以封装成map，实际上如果你在传入参数的时候，在MyBatis里面也是会把它封装成一个Map的，map的key就是参数名，所以这个时候collection属性值就是传入的List或array对象在自己封装的map里面的key.
下面我们通过代码实践:

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());

    }