MyBatis參數傳入集合之foreach動態sql

foreach的主要用在構建in條件中，它可以在SQL語句中進行迭代一個集合。foreach元素的屬性主要有item，index，collection，open，separator，close。item表示集合中每一個元素進行迭代時的別名，index指定一個名字，用於表示在迭代過程中，每次迭代到的位置，open表示該語句以什么開始，separator表示在每次進行迭代之間以什么符號作為分隔符，close表示以什么結束，在使用foreach的時候最關鍵的也是最容易出錯的就是collection屬性，該屬性是必須指定的，但是在不同情況下，該屬性的值是不一樣的，主要有一下3種情況： 

1. 如果傳入的是單參數且參數類型是一個List的時候，collection屬性值為list .
2. 如果傳入的是單參數且參數類型是一個array數組的時候，collection的屬性值為array .
3. 如果傳入的參數是多個的時候，我們就需要把它們封裝成一個Map了，當然單參數也可以封裝成map，實際上如果你在傳入參數的時候，在MyBatis里面也是會把它封裝成一個Map的，map的key就是參數名，所以這個時候collection屬性值就是傳入的List或array對象在自己封裝的map里面的key.

下面我們通過代碼實踐:

 

數據表:

采用Oracle的HR.Employees表

        實體: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屬性類型是List,collection的值必須是:list,item的值可以隨意,Dao接口中參數名字隨意 -->
    <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屬性類型是array,collection的值必須是:list,item的值可以隨意,Dao接口中參數名字隨意 -->
    <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:不單單forech中的collection屬性是map.key,其它所有屬性都是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>

 

判斷可以用

<choose>
<when test="null!=list and list.size!=0">
AND OI.ORDER_NO IN
<foreach collection="list" item="orderNo" index="index"
open="(" separator="," close=")">
#{orderNo}
</foreach>
</when>
<otherwise>
AND 1 != 1
</otherwise>
</choose>

Mapper類:
public interface EmployeesMapper { 

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

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

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

測試方法(未貼完整代碼):

    @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" };
        // 傳入多個參數
        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());
    }