Question

在SQL中，使用字符串连接进行参数化查询非常简单。例如，我根据预设参数从DB表中获取必要的列（带有列＆＃39;名称的字符串）

String id_column = "id", city_column = "city", streetname_column ="streetname", housenumber_column = "housenumber"; //Parameters
        stmt = c.createStatement();
        ResultSet rs = stmt.executeQuery( "SELECT "+id_column+","+streetname_column+" FROM address" ); //How do the same in QueryDSL?
        ResultSetMetaData rsmd = rs.getMetaData();
        for (int i = 0; i < rsmd.getColumnCount(); i++){
            System.out.print(rsmd.getColumnName(i+1)+" ");
        }
        while ( rs.next() ) {
            System.out.print("\n");
            for (int i = 0; i < rsmd.getColumnCount(); i++){
                System.out.print(
                        rs.getString(rsmd.getColumnName(i+1)) + " "
                );
            }
        }

我怎么能这样做（你也可以自己做例子）QueryDSL请求：

List<Address> q1=queryFactory.selectFrom(address)
                    .fetch();

在这个查询中，我得到了整个表格。

Answer 1

最后，我找到了答案。解决方案位于此页面： Examples of using play.db.jpa.JPAApi

在我的问题的背景下，解决方案如下：

package controllers;
import play.db.jpa.JPAApi;
import play.db.jpa.Transactional;
import javax.inject.Inject;
import javax.persistence.Query;
import java.util.ArrayList;
import java.util.List;

public class TestingReportsDep{

private JPAApi jpaApi;
@Inject
public TestingReportsDep(JPAApi jpaApi) {
    this.jpaApi = jpaApi;
}
Object[] tempObj;

@Transactional
public void resolving_requests) {
    String id_column = "id", city_column = "city", streetname_column ="streetname", housenumber_column = "housenumber"; //Parameters
    String request="SELECT "+id_column+","+streetname_column+" FROM address;";
    jpaApi.withTransaction(entityManager -> {
        Query query = entityManager.createNativeQuery(request);
        int ResultsAmount = query.getResultList().size();
        List Result = query.getResultList();
        System.out.print("\n\n\nNew super query by Bogdan:\n");

        for(int i=0; i< ResultsAmount; i++){
            tempObj = (Object[]) Result.get(i);

            System.out.print(tempObj[0]+" "+tempObj[1]+"\n");
        }
        return null;
    });
 }
}

带参数的QueryDSL请求是否可能？

1 个答案: