JPA mappedBy引用未知的目标实体

Question

我正在编写一个简单的库存数据库，其中包含产品、订单和客户的表。数据库定义可以在这里找到：

CREATE TABLE public.customers
(
id integer NOT NULL DEFAULT nextval('customers_id_seq'::regclass),
title character varying(10) COLLATE pg_catalog."default" NOT NULL,
first_name character varying(50) COLLATE pg_catalog."default" NOT NULL,
middle_names character varying(50) COLLATE pg_catalog."default",
last_name character varying(50) COLLATE pg_catalog."default" NOT NULL,
email character varying(50) COLLATE pg_catalog."default" NOT NULL,
phone_number character varying(50) COLLATE pg_catalog."default" NOT NULL,
CONSTRAINT customers_pkey PRIMARY KEY (id)
)
CREATE TABLE public.products
(
id integer NOT NULL DEFAULT nextval('products_id_seq'::regclass),
name character varying(100) COLLATE pg_catalog."default" NOT NULL,
sku integer NOT NULL,
inventory_on_hand integer NOT NULL,
reorder_threshold integer NOT NULL,
price numeric(5,2),
inventory_to_be_shipped integer NOT NULL,
CONSTRAINT products_pkey PRIMARY KEY (id)
)
CREATE TABLE public.order_items
(
id integer NOT NULL DEFAULT nextval('order_items_id_seq'::regclass),
product_id integer NOT NULL,
order_id integer NOT NULL,
CONSTRAINT order_items_pkey PRIMARY KEY (id),
CONSTRAINT order_items_order_id_fkey FOREIGN KEY (order_id)
REFERENCES public.orders (id) MATCH SIMPLE
ON UPDATE NO ACTION
ON DELETE NO ACTION,
CONSTRAINT order_items_product_id_fkey FOREIGN KEY (product_id)
REFERENCES public.products (id) MATCH SIMPLE
ON UPDATE NO ACTION
ON DELETE NO ACTION
)
CREATE TABLE public.orders
(
id integer NOT NULL DEFAULT nextval('orders_id_seq'::regclass),
customer_id integer,
order_date date NOT NULL DEFAULT now(),
arrival_date date,
CONSTRAINT orders_pkey PRIMARY KEY (id),
CONSTRAINT orders_customer_id_fkey FOREIGN KEY (customer_id)
REFERENCES public.customers (id) MATCH SIMPLE
ON UPDATE NO ACTION
ON DELETE NO ACTION
)

我正在尝试实现一个Spring Security Resource服务器来对数据库执行CRUD操作。我已经为数据库中的每个表实现了实体类，但当尝试启动服务器时，我会得到一个

org.hibernate.AnnotationException: mappedBy reference an unknown target entity property: edu.finalyearproject.imsresourceserver.models.Order.customers in edu.finalyearproject.imsresourceserver.models.Customer.orders

我的实体和存储库类可以在下面找到：

产品.java：

@Entity
@Table(name = "products")
@Data
public class Product
{
@Id
@GeneratedValue(strategy= GenerationType.IDENTITY)
private Integer id;
private String name;
private Integer sku;
private Float price;
private Integer inventory_on_hand;
private Integer reorder_threshold;
@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.LAZY)
@JoinTable(
name = "order_items",
joinColumns = @JoinColumn(name = "product_id"),
inverseJoinColumns = @JoinColumn(name = "order_id")
)
private Set<Order> orders = new HashSet<>();
}

客户.java

@Entity
@Table(name = "customers")
@Data
public class Customer
{
@Id
@GeneratedValue(strategy= GenerationType.IDENTITY)
private Integer id;
private String title;
private String first_name;
private String middle_names;
private String last_name;
private String email;
private String phone_number;
@OneToMany(mappedBy = "customer", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<Order> orders;
}

订单.java

@Entity
@Table(name = "orders")
@Data
public class Order
{
@Id
@GeneratedValue(strategy= GenerationType.IDENTITY)
private Integer id;
@ManyToOne
@JoinColumn(name="customer_id", nullable=false)
private Customer customer;
private Date order_date;
private Date arrival_date;
@ManyToMany(mappedBy = "orders", cascade = {CascadeType.PERSIST, CascadeType.MERGE})
private Set<Product> products = new HashSet<>();
}

我知道这个问题与实体之间的关系有关，但我一直未能找到解决方案。如有任何帮助，我们将不胜感激。

Answer 1

尝试更正此问题：

@Entity
public class Customer
{
// ...
@OneToMany(mappedBy = "orders", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<Order> orders;
}

到此：

@Entity
public class Customer
{
// ...
@OneToMany(mappedBy = "customer", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Set<Order> orders;
}

请参阅文档中的其他说明。

您还应该更正您的Product-Order@ManyToMany关联。只有此关联的一侧应使用@JoinTable，另一侧应使用@ManyToMany注释的mappedBy属性。类似这样的东西：

@Entity
public class Product
{
// ...
@ManyToMany(
cascade = {CascadeType.PERSIST, CascadeType.MERGE},
fetch = FetchType.LAZY
)
@JoinTable(
name = "order_items",
joinColumns = @JoinColumn(name = "product_id"),
inverseJoinColumns = @JoinColumn(name = "order_id")
)
private Set<Order> orders = new HashSet<>();
}
@Entity
public class Order
{
// ...
@ManyToMany(
mappedBy = "orders",
cascade = {CascadeType.PERSIST, CascadeType.MERGE},
fetch = FetchType.LAZY)
private Set<Product> products = new HashSet<>();
}

正如文件中所述：

对于@ManyToMany关联，REMOVE实体状态转换级联没有意义，因为它将传播到链接表之外。由于另一侧可能被父侧的其他实体引用，因此自动删除可能会以ConstraintViolationException结束。

正如本节文档中所解释的：

如果您忘记了JOIN FETCH所有EAGER关联，Hibernate将为每一个关联发出二次选择，这反过来会导致N+1查询问题。

因此，您应该更喜欢LAZY关联