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 //注入的是實體管理器,執行持久化操作
    EntityManager entityManager;

    public String getInfoWebWaring(String column){
        String SQL = "SELECT "+column+" FROM config LIMIT 1";
        Object obj = entityManager.createNativeQuery(SQL).getSingleResult();

        return String.valueOf(obj);
    }
    
    public WebInfo getWebInfo(String [] args){

        String SQL = "SELECT id, "+
                args[0]+" log_url, "+
                args[1]+" title, "+
                args[2]+" key_word, "+
                args[3]+" description, "+
                args[4]+" address, "+
                args[5]+" contact "+
                "FROM config LIMIT 1";

        WebInfo webInfo = (WebInfo) entityManager.createNativeQuery(SQL,WebInfo.class).getSingleResult();

        return 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  //注入informationDaoEM
    private InformationDaoEM informationDaoEM;

    @Override
    public String getWebWaring(String column) {

        return informationDaoEM.getInfoWebWaring(column);
    }

    @Override
    public WebInfo getWebInfo(String[] args) {

        return informationDaoEM.getWebInfo(args);
    }

    


}