mybatis传入集合类型参数 动态sql构建

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:Employeespublic 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());    }