SpringBoot JPA relationsships-如果对象存在，则防止创建新的实体，而是返回已经存在的对象

Question

我有一个用控制器、服务和存储库逻辑构建的客户实体。

我还有一个Address实体，只有一个简单的POJO和@OneTomany注释。

如果我用相同的地址属性发出两个POST请求--如果这些地址属性已经存在于数据库中，我如何告诉我的应用程序--阻止在数据库中添加新实体，而是返回已经存在的实体？

例如。员额请求：

// First request
{
    "name": "Foo",
    "contact": "123456",
    "email": "[e-mail]",
    "address": {
        "street": "Wall street", 
        "postalCode": 10,
        "houseNo": "45",
        "city": "New York"
    }
}

// Second request
{
    "name": "Bar",
    "contact": "5321",
    "email": "[e-mail]",
    "address": {
        "street": "Wall street", <----- same as first request
        "postalCode": 10, <----- same as first request
        "houseNo": "45", <----- same as first request
        "city": "New York" <----- same as first request
    }
}

这是获取所有客户时的结果：

[
    {
        "id": 1,
        "name": "Foo",
        "contact": "123456",
        "email": "[e-mail]",
        "address": {
            "id": 1,
            "street": "Wall street",
            "postalCode": 10,
            "houseNo": "45",
            "city": "New York"
        }
    },
    {
        "id": 2,
        "name": "Bar",
        "contact": "5321",
        "email": "[e-mail]",
        "address": {
            "id": 2, <---------------- expect this ID to be 1 
            "street": "Wall street",
            "postalCode": 10,
            "houseNo": "45",
            "city": "New York"
        }
    }
]

这里是必要的信息(if)需要帮助我进行我的小项目。

customer.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;
    [...]

@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;
    [...]

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

[...]

和将客户保存到数据库的服务：

//...
public void createCustomer(Customer customer) {
        customerRepository.save(customer);
    }

[...]

Answer 1

您可以用您的地址参数创建一个散列，并保持类似；

"street": "Wall street",
"postalCode": 10,
"houseNo": "45",
"city": "New York"
"uid": "3rn3u924917vt8r78b17vxver"

当您获得一个新地址时，可以用它创建一个散列，并用该散列获得地址。如果该散列中存在任何地址，则获取该地址并将其放入customer对象中并保存。