MyBatis參數傳入集合之foreach動態sql

foreach的主要用在構建in條件中，它能夠在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當中，每次迭代到的位置，open表示該語句以什麼開始，separator表示在每次進行迭代之間以什麼符號做爲分隔符，close表示以什麼結束，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，可是在不一樣狀況下，該屬性的值是不同的，主要有一下3種狀況： 

1. 若是傳入的是單參數且參數類型是一個List的時候，collection屬性值爲list .
2. 若是傳入的是單參數且參數類型是一個array數組的時候，collection的屬性值爲array .
3. 若是傳入的參數是多個的時候，咱們就須要把它們封裝成一個Map了，固然單參數也能夠封裝成map，實際上若是你在傳入參數的時候，在MyBatis裏面也是會把它封裝成一個Map的，map的key就是參數名，因此這個時候collection屬性值就是傳入的List或array對象在本身封裝的map裏面的key.

下面咱們經過代碼實踐:

 

數據表:

採用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的值能夠隨意,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的值能夠隨意,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:不僅僅forech中的collection屬性是map.key,其它全部屬性都是map.key,好比下面的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>

 

判斷能夠用

<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());     }