tasks表对应的Entity
@Entity
@NoArgsConstructor
@AllArgsConstructor
@Table(name = "tasks")
@Data
public class Tasks extends BaseEntity {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int taskId;
private Integer websiteId;
private String status;
private String lastOperator;
private String lastOperationTime;
private String jobId;
private int retryTimes;
}websites表对应的Entity
@Entity
@Table(name = "websites")
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Websites extends BaseEntity{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int websiteId;
private String country;
private String websiteName;
private String baseUrl;
private String smartphoneUrl;
private String tabletUrl;
private String smartdeviceUrl;
private String websiteCategory;
private String webtypeRefreshRate;
private String urlRefreshRate;
private String configTime;
private String configDesc;
}自定义对象
@Data
@NoArgsConstructor
@AllArgsConstructor
public class CustomizedDto implements Serializable {
private static final long serialVersionUID = -7242005560621561106L;
private String country;
private String websiteName;
private String baseUrl;
private String status;
}方法一、简单查询直接new对象
使用hql，将结果返回到new出来的自定义对象中，注意，自定义对象中要有对应的构造函数。
@Query(value = "select new com.bigdata.mrcrawler.dto.CustomizedDto(w.country,w.websiteName,w.baseUrl,t.status) "
"from Websites w join Tasks t on w.id=t.websiteId "
"where t.status=?1")
List<CustomizedDto> getByStatus1(String status);但是这个方法只使用于简单的查询语句，如果遇到复杂查询需要使用原生SQL（即nativeQuery=true）时， 此方法不适用，会抛出如下异常。
@Query(value = "select w.country as country,w.website_name as websiteName,w.base_url as baseUrl,t.status as status "
"from websites w join tasks t on w.website_id=t.website_id "
"where t.status=?1",nativeQuery = true)
List<CustomizedDto> getByStatus2(String status);No converter found capable of converting from type [org.springframework.data.jpa.repository.query.AbstractJpaQuery$TupleConverter$TupleBackedMap] to type [com.bigdata.mrcrawler.dto.CustomizedDto]
方法二、Service层使用EntityManager
直接在Service层使用EntityManager进行查询，可以自由组装各种复杂sql。
public List<CustomizedDto> t(String param) {
String sql = "select w.country as country,w.website_name as websiteName,w.base_url as baseUrl,t.status as status "
"from websites w join tasks t on w.website_id=t.website_id "
"where t.status='" param "'";
List<CustomizedDto> res = entityManager.createNativeQuery(sql).getResultList();
return res;
}但是会有sql注入问题，例如：param传入Running' or 1=1 --\t 上述查询会将查询整个数据表。解决方法如下，使用预编译防止sql注入问题。
public List<CustomizedDto> t(String param) {
String sql = "select w.country as country,w.website_name as websiteName,w.base_url as baseUrl,t.status as status "
"from websites w join tasks t on w.website_id=t.website_id "
"where t.status=:param" ;
Query nativeQuery = entityManager.createNativeQuery(sql);
nativeQuery.setParameter("param", param);
List<CustomizedDto> res = nativeQuery.getResultList();
return res;
}然而，个人很不喜欢这种代码中嵌入大片大片sql的写法，排查问题的时候看得头疼（别问，问就是被坑过/捂脸.jpg/）。所以方法二即便可行，我私心还是不想推荐。
方法三、Dao层使用Map接收自定义对象
使用List<Map> 接收返回结果，无论是原生sql还是hql都支持，当然也支持分页，只需要把返回对象改为Page<Map>即可，其他操作与普通分页没有差别。
@Query(value = "select w.country as country,w.website_name as websiteName,w.base_url as baseUrl,t.status as status "
"from websites w join tasks t on w.website_id=t.website_id "
"where t.status=?1",nativeQuery = true)
List<Map> getByStatus3(String status);Service层也需要用List<Map>进行接收。
public List<Map> t(String param) {
return testRepository.getByStatus3(param);
}如果后续还有其他操作，还是需要转成自定义对象怎么办，毕竟Map操作起来挺麻烦的。可以用如下解决方案，先用Object进行接收，然后强转成自定义对象List。
public List<CustomizedDto> t(String param) {
Object data = testRepository.getByStatus3(param);
return (List<CustomizedDto>)data;
}强转需要注意自定义对象和数据库中字段类型的强一致性，如数据库中datetime类型，自定义对象对应的字段必须是Date，不能是String，否则转换的时候会有问题，数据会丢失。
总结
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