我有两个实体：客户和地址。
这是一种***双向关系***-一个地址可以有多个客户（oneToMany），而一个客户只能有一个地址（manyToOne）。
执行客户退货的GET请求：

[
    {
        "id": 1,
        "name": "Foo",
        "contact": "5512312",
        "email": "Foo@gmail.com",
        "address": {
            "id": 1,
            "street": "X",
            "postalCode": 123,
            "houseNo": "10",
            "city": "New York"
        }
    }
]

当使用POST请求添加一个新客户（其地址属性与DB中存在的客户完全相同）时，json响应返回与DB中现有对象相关的外键，而不是对象本身：

[
    {
        "id": 1,
        "name": "Foo",
        "contact": "5512312",
        "email": "Foo@gmail.com",
        "address": {
            "id": 1,
            "street": "X",
            "postalCode": 123,
            "houseNo": "10",
            "city": "New York"
        }
    },
    {
        "id": 2,
        "name": "Bar",
        "contact": "5512312",
        "email": "Bar@gmail.com",
        "address": 1 <----------- it returns the foreign key instead of the object
    }
]

因此，我期望的是，每当添加一个新客户时，如果该客户的地址 * 已经存在于数据库中 *，那么它应该返回 *address对象 *，而不是json响应中的外键。
验证码：

客户.java

@JsonIdentityInfo(
        generator = ObjectIdGenerators.PropertyGenerator.class,
        property = "id")
@Entity
@Table
public class Customer {
    @Id
    @SequenceGenerator(
            name = "customer_sequence",
            sequenceName = "customer_sequence",
            allocationSize = 1
    )
    @GeneratedValue(
            strategy = GenerationType.SEQUENCE,
            generator = "customer_sequence"
    )
    private Long id;
    private String name;
    private String contact;
    private String email;

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "address_id", nullable = false)
    private Address address;
    [...]

地址.java

@JsonIdentityInfo(
        generator = ObjectIdGenerators.PropertyGenerator.class,
        property = "id")
@Entity
@Table
public class Address {
    @Id
    @SequenceGenerator(
            name = "address_sequence",
            sequenceName = "address_sequence",
            allocationSize = 1
    )
    @GeneratedValue(
            strategy = GenerationType.SEQUENCE,
            generator = "address_sequence"
    )
    private Long id;
    private String street;
    private int postalCode;
    private String houseNo;
    private String city;

    @JsonIgnore
    @OneToMany(mappedBy = "address")
    private Set<Customer> customers;
    [...]

CustomerController.java

//...
@PostMapping
    public void createCustomer(@RequestBody Customer customer) {
        customerService.createCustomer(customer);
    }

[...]

而***service***将客户保存到DB中，这也确保如果数据库中已经存在地址，则不会创建地址（它检查每个属性是否与参数相等）：

//...
public void createCustomer(Customer customer) {
        Optional<Customer> customerWithExistingAddress = customerRepository.findAll()
                .stream()
                .filter(x -> x.getAddress().equals(customer.getAddress()))
                .findFirst();

        customerWithExistingAddress.ifPresent(c -> customer.setAddress(c.getAddress()));

        customerRepository.save(customer);
    }

[...]