JPA框架下使用純粹的原生SQL

　　最近遇到一個需求，查詢數據庫中對應表的字段是動態的，項目使用的框架使用JPA+Spring Boot，JPA自帶原生SQL支持的傳入參數是強類型的，無法用於查詢語句的字段更改，因為插入字符串的話帶有單引號，需要另外定義原生SQL

因此我們創建一個查詢類

import com.weiqitonggame.trade.model.WebInfo;
import org.springframework.stereotype.Component;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
@Component //標記為組件，spring啟動時會將該類掃描進容器
 public class InformationDaoEM {
@PersistenceContext </span><span style="color: #008000;">//</span><span style="color: #008000;">注入的是實體管理器,執行持久化操作</span>

 EntityManager entityManager;
</span><span style="color: #0000ff;">public</span><span style="color: #000000;"> String getInfoWebWaring(String column){
    String SQL </span>= "SELECT "+column+" FROM config LIMIT 1"<span style="color: #000000;">;
    Object obj </span>=<span style="color: #000000;"> entityManager.createNativeQuery(SQL).getSingleResult();

    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> String.valueOf(obj);
}

</span><span style="color: #0000ff;">public</span><span style="color: #000000;"> WebInfo getWebInfo(String [] args){

    String SQL </span>= "SELECT id, "+<span style="color: #000000;">
            args[</span>0]+" log_url, "+<span style="color: #000000;">
            args[</span>1]+" title, "+<span style="color: #000000;">
            args[</span>2]+" key_word, "+<span style="color: #000000;">
            args[</span>3]+" description, "+<span style="color: #000000;">
            args[</span>4]+" address, "+<span style="color: #000000;">
            args[</span>5]+" contact "+
            "FROM config LIMIT 1"<span style="color: #000000;">;

    WebInfo webInfo </span>= (WebInfo) entityManager.createNativeQuery(SQL,WebInfo.<span style="color: #0000ff;">class</span><span style="color: #000000;">).getSingleResult();

    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> webInfo;
}

}

其中
EntityManager.createNativeQuery(SQL)返回的是Object對象
entityManager.createNativeQuery(SQL,WebInfo.class)返回的是映射后的實例對象
實體類WebInfo需要進行以下處理，確保被掃描進spring容器

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.experimental.Accessors;
import javax.persistence.*;
@Data //生成讀寫方法
 @AllArgsConstructor //生成全參構造方法
 @NoArgsConstructor //生成無參構造方法
 @Accessors(chain = true)
 @Entity(name = "tableName") //標記為entity
 public class WebInfo {
 @Id
 @GeneratedValue(strategy= GenerationType.AUTO)
 @Column(name = "id") //查詢結果對應字段
 private Integer id;
 @Column(name = "log_url")
 private String logUrl;
 @Column(name = "title")
 private String title;
 @Column(name = "key_word")
 private String keyWord;
 @Column(name = "description")
 private String description;
 @Column(name = "address")
 private String address;
 @Column(name = "contact")
 private String contact;
}

Query.getSingleResult() 執行SQL語句，返回一個查詢結果，常用的還有以下方法
Query.getResultList() () 執行SQL語句，返回一個List集合
Query.getFirstResult() () 執行SQL語句，返回一個系列結果集合的第一個

 調用方式如下:

import org.springframework.stereotype.Service;
import com.weiqitonggame.trade.service.InformationService;
import org.springframework.beans.factory.annotation.Autowired;
import com.weiqitonggame.trade.dao.InformationDaoEM;
import com.weiqitonggame.trade.model.WebInfo;
@Service //標記為service
 public class InformationServiceImpl implements InformationService {
@Autowired  </span><span style="color: #008000;">//</span><span style="color: #008000;">注入informationDaoEM</span>
<span style="color: #0000ff;">private</span><span style="color: #000000;"> InformationDaoEM informationDaoEM;

@Override
</span><span style="color: #0000ff;">public</span><span style="color: #000000;"> String getWebWaring(String column) {

    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> informationDaoEM.getInfoWebWaring(column);
}

@Override
</span><span style="color: #0000ff;">public</span><span style="color: #000000;"> WebInfo getWebInfo(String[] args) {

    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> informationDaoEM.getWebInfo(args);
}

}