MyBatis参数传入集合之foreach动态sql
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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()); }
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