我正在尝试使用Spring Boot重新创建一个旧的J2EE项目，以此作为学习练习，并且在处理这个映射问题上遇到了一些困难。当我尝试提取`User`实体的结果集时，我一直遇到**在'字段列表'中的未知列'user0_.user_id'**的问题，类似地，对于`Product`实体也是一样的。
请查看我的模式。
[![我的模式的EER图][1]][1]
  [1]: https://i.stack.imgur.com/7WolU.png
这是我的实体：
```java
@Entity
public class User {
	
	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	private int userId;
	
	private String firstName;
	
	private String lastName;
	
	private String email;
	
	private String username;
	
	private String password;
	
	private String roleName;
	
	@OneToMany(mappedBy = "userJ")
	private List<Card> cards;
	// 构造函数和getter/setter....
}

@Entity
public class Card {
	
	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private int cardId;
	
	private String cardNumber;
	
	private String cardType;
	
	private String expiryMonth;
	
	private String expiryYear;
	
	private String cardHolder;
	
	@ManyToOne
	@JoinColumn(name = "userId")
	private User userJ;
	
	@OneToMany(mappedBy = "cardJ")
	private List<Purchase> purchases;
	
    // 构造函数和getter/setter....
}

@Entity
public class Purchase {
	
	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private int purchaseId;
	
	private String notes;
	
	@Basic
	private Timestamp purchaseDate;
	
	@ManyToOne
	@JoinColumn(name = "cardId")
	private Card cardJ;
	
	@OneToMany(mappedBy="purchaseJ")
	private List<PurchaseItem> purchaseItems;
	
    // 构造函数和getter/setter....
}

@Entity
public class PurchaseItem {
	
	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private int purchaseItemId;
	
	private int quantity;
	
	private BigDecimal price;
	
	@ManyToOne
	@JoinColumn(name="purchaseId")
	private Purchase purchaseJ;
	
	@ManyToOne
	@JoinColumn(name="productId")
	private Product productJ;
	
    // 构造函数和getter/setter....
}

@Entity
public class Product {
	
	@Id
	private String productId;
	
	private String manufacturer;
	
	private String item;
	
	private String description;
	
	private BigDecimal price;
	
	@Column(nullable = false, columnDefinition = "TINYINT(1)")
	private byte available;
	
	@OneToMany(mappedBy = "productJ")
	private List<PurchaseItem> purchaseItems;
	
    // 构造函数和getter/setter....
}

@Repository
@Transactional
public class UserDAOImpl implements UserDAO {
	@Autowired
	public EntityManager entityManager;
	
	@Override
	public List<User> showUsers() {
		
		return entityManager.createQuery("Select u from User u", User.class).getResultList();
	}
}

@RestController
@RequestMapping("/api")
public class SheridanSportsRESTController {
	
	@Autowired
	private UserDAO userDAO;
	
	@Autowired
	private ProductDAO productDAO;
	
	@GetMapping("/users")
	public List<User> showUsers(){
		
		return userDAO.showUsers();
	}
	
	@GetMapping("/products")
	public List<Product> showProducts(){
		
		return productDAO.showProducts();
	}
}

<details>
<summary>英文:</summary>
I am trying re-create an older J2EE project with Spring Boot as a learning exercise and have been stuck on this mapping issue for a bit. When I try to extract Result Set for my `User` entity, I keep running into **Unknown column &#39;user0_.user_id&#39; in &#39;field list&#39;** and similarly with `Product` entity as well.
Please take a look at my schema.
[![EER diagram for my schema][1]][1]
  [1]: https://i.stack.imgur.com/7WolU.png
And here are my entities:

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int userId;
private String firstName;
private String lastName;
private String email;
private String username;
private String password;
private String roleName;
@OneToMany(mappedBy = "userJ")
private List<Card> cards;
//constructors and getters/setters....

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int cardId;
private String cardNumber;
private String cardType;
private String expiryMonth;
private String expiryYear;
private String cardHolder;
@ManyToOne
@JoinColumn(name = "userId")
private User userJ;
@OneToMany(mappedBy = "cardJ")
private List<Purchase> purchases;
//constructors and getters/setters....

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int purchaseId;
private String notes;
@Basic
private Timestamp purchaseDate;
@ManyToOne
@JoinColumn(name = "cardId")
private Card cardJ;
@OneToMany(mappedBy="purchaseJ")
private List<PurchaseItem> purchaseItems;
//constructors and getters/setters....

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int purchaseItemId;
private int quantity;
private BigDecimal price;
@ManyToOne
@JoinColumn(name="purchaseId")
private Purchase purchaseJ;
@ManyToOne
@JoinColumn(name="productId")
private Product productJ;
//constructors and getters/setters....

@Id
private String productId;
private String manufacturer;
private String item;
private String description;
private BigDecimal price;
@Column(nullable = false, columnDefinition = "TINYINT(1)")
private byte available;
@OneToMany(mappedBy = "productJ")
private List<PurchaseItem> purchaseItems;
//constructors and getters/setters....

My DAO:

@Autowired
public EntityManager eman;
@Override
public List<User> showUsers() {
	
	return eman.createQuery("Select u from User u", User.class).getResultList();
}

My Rest Controller:

@Autowired
private UserDAO userDAO;
@Autowired
private ProductDAO productDAO;
@GetMapping("/users")
public List<User> showUsers(){
	
	return userDAO.showUsers();
}
@GetMapping("/products")
public List<Product> showProducts(){
	
	return productDAO.showProducts();
}

And I did not use `@ManyToMany` on my join table because of the extra properties in `PurchaseItem`.
</details>
# 答案1
**得分**: 1
Sure, here's the translated content:
你需要在 userId 属性中加入列注解，就像这样：
```java
@Column(name="UserId")
private Integer userId;