Spring Boot JPA如何从带有实体类的表中选择特定的列? [英] Spring Boot JPA how to select specific column from table with the entity class?

问题描述

我正在使用spring boot JPA进行数据库操作.在我的实体类中，我将每个列与表进行映射.在我的表中，我有很多列，但是我需要在查询结果集中选择其中的一些.我不需要执行select * from table_name即可将性能问题带到我的应用程序中.

In am using spring boot JPA for my database operations. In my entity class, I mapped every columns with my table. In my table I have many columns, but I need to select some of them in my query result set. I does not need to do select * from table_name which brings the performance issue to my application.

我的实体类:

@Entity
@Table(name = "user_table")
public class UserInformation {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "user_id")
    private int userId;

    @Column(name = "user_name")
    private String userName;

    @Column(name = "user_type")
    private String userType;

    @Column(name = "user_age")
    private int userAge;

    @Column(name = "is_male")
    private boolean isMale;
}

此后，我生成了上述类的所有吸气剂和吸气剂.

After this I generated all getters and setters for above class.

我的userDAO类

public interface UserInformationRepo extends 
         JpaRepository<UserInformation, String>{

    @Query(value="select user_name from user_table where user_age > 
               :userAge", nativeQuery=true)
    public UserInformation getInfo(int userAge);\

    @Query(value="select user_name,userType, user_id  from user_table where 
          user_age > :userAge", nativeQuery=true)
    public UserInformation getInfo(int userAge);
}

当我使用上述类运行此春季启动应用程序时，它显示错误为

When I run this spring boot app with my above class it shows error as

user_id未包含在结果集中

user_id was not included in the ResultSet

此错误是因为我没有从查询中选择user_id.

This error because I did't select the user_id from my query.

在我的userDAO类中，我有多个函数，每个函数需要不同的列集，但是所有方法的返回类型应该是UserInformation类.

In my userDAO class I have a multiple functions, each functions need different set of columns, but the return type of all methods should be UserInformation class.

我的例外结果是，我未从查询中选择的列在我的结果UserInformation对象中应为空值.

My excepted result is, the columns which I does not select from query should have null value in my result UserInformation object.

我也为此搜索了很多资源，但是找不到任何相关的答案.

I also searched many resources for this, but I cannot find any relevant answer.

任何帮助.预先感谢

推荐答案

一种方法是使用userId和userName创建UserInformation的构造函数.

One way could be create a constructor of the UserInformation with userId and userName.

package com.demo.model;

public UserInformation( String userName, String userType, String userId){
    this.userName = userName;
    this.userType = userType;
    this.userId = userId;
}

然后

 @Query(value="select new com.demo.model.UserInformation
               (user_name,userType, user_id)  
                from user_table where 
                user_age > :userAge", nativeQuery=true)

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