Question

我正在为练习项目在线购物系统开发简单的API。由于我是使用API的新手，因此我的实体和关系出现问题。首先，在介绍问题之前，我给出了所有的模式和类。

这是我的数据库架构的link。

这些是@Entity类：

----
@Entity
@Table(name = "Customer")
public class Customer {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "id")
private int id;

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

@Column(name = "country")
private String country;

@OneToMany(mappedBy = "customer", cascade = CascadeType.ALL, orphanRemoval = true)
private List<Order> orders = new ArrayList<>();

// constructor, getters, setters ....


@Entity
@Table(name = "Order")
public class Order {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "id")
private int id;

@Column(name = "date")
private Date date;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "cust_id", nullable = false)
@JsonIgnore
private Customer customer;

@OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
private List<Detail> details = new ArrayList<>();

@OneToMany(mappedBy = "order", cascade = CascadeType.ALL, orphanRemoval = true)
private List<Invoice> invoices = new ArrayList<>();

//constructor, setters, getters ....

@Entity
@Table(name = "Product")
public class Product {

@Id
@GeneratedValue
@Column(name = "id")
private int id;

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

@Column(name = "description")
private String description;

@Column(name = "price")
private Double price;

@OneToMany(mappedBy = "product", cascade = CascadeType.ALL, orphanRemoval = true)
private List<Detail> orderDetails = new ArrayList<>();

//cons, setters, getters ...

@Entity
@Table(name = "Detail")
public class Detail {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "ord_id", nullable = false)
@JsonIgnore
private Order order;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "pr_id", nullable = false)
@JsonIgnore
private Product product;

@Column(name = "quantity")
private int quantity;

//similar classes for Invoice and Payment (no problem with them)

这是我的Sample Repository类：

@Repository
public interface ProductRepository extends JpaRepository<Product, Integer> {

}

这是我的控制器类：

@RestController
public class OnlineShoppingApiController {
@Autowired
ProductRepository productRepository;

@Autowired
OrderRepository orderRepository;

@Autowired
CustomerRepository customerRepository;

@Autowired
DetailRepository detailRepository;

@Autowired
InvoiceRepository invoiceRepository;

@Autowired
PaymentRepository paymentRepository;

@GetMapping("/products")
public List<Product> getProductsList(){
    return productRepository.findAll();
}

@GetMapping("/customers")
public List<Customer> getCustomersList(){
    return customerRepository.findAll();
}

@GetMapping("/orders")
public List<Order> getOrdersList(){
    return orderRepository.findAll();
}

@GetMapping("/invoices")
public List<Invoice> getInvoicesList(){
    return invoiceRepository.findAll();
}

@GetMapping("/payments")
public List<Payment> getPaymentsList(){
    return paymentRepository.findAll();
}

@GetMapping("/details")
public List<Detail> getDetailsList(){
    return detailRepository.findAll();
}

我对所有API和关系采用相同的方法。

当我在邮递员中呼叫/产品时，我得到的结果是JSON：

[{
    "id": 3,
    "name": "pname_816",
    "description": "pdesc_871_871_871_87",
    "price": 1.41,
    "orderDetails": [
        {
            "id": 9,
            "quantity": 831
        },
        {
            "id": 51,
            "quantity": 701
        },
        {
            "id": 87,
            "quantity": 310
        }
    ]
},
{
    "id": 4,
    "name": "pname_395",
    "description": "pdesc_495_495_495_49",
    "price": 26.65,
    "orderDetails": [
        {
            "id": 85,
            "quantity": 853
        }
    ]
}]

/details，/invoices和/payments的结果相同。

问题是如果我发送/customers的GET请求，结果是：

{
"timestamp": "2018-04-05T11:53:39.558+0000",
"status": 500,
"error": "Internal Server Error",
"message": "Could not write JSON: could not extract ResultSet; nested exception is com.fasterxml.jackson.databind.JsonMappingException: could not extract ResultSet (through reference chain: java.util.ArrayList[0]->com.example.project.pojo.Customer[\"orders\"])",
"path": "/customers"
}

如果我发送/orders请求，结果是：

{
"timestamp": "2018-04-05T11:54:37.316+0000",
"status": 500,
"error": "Internal Server Error",
"message": "could not extract ResultSet; SQL [n/a]; nested exception is org.hibernate.exception.SQLGrammarException: could not extract ResultSet",
"path": "/orders"
}

同样的方法并非适用于所有人。我无法理解问题出在哪里。请帮我找到它。

感谢您的回答

Answer 1

我终于找到了自己的答案。这里的问题不在于注释或键引用，而在于命名实体。

由于order是MySql的保留关键字，因此命名实体和这样的变量会导致意外问题。

所以我刚刚在架构和代码中将实体名称更改为Orders并且工作正常。

希望这篇文章对其他人也有帮助

在JpaRepository中使用外键

1 个答案: