java - JPA mappedBy reference an unknown target entity

Question

I am writing a simple inventory database that contains tables for products, orders and customers. The database definition can be found here:

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
)

I am trying to implement a Spring Security Resource server to perform CRUD operations on the database. I have implemented entity classes for each table in the database but when try to start the server I get a

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

My entity and repository classes can be found below:

Product.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<>();
}

Customer.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;
}

Order.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<>();
}

I know the problem is related to the relationships between the entities, but I haven't been able to find a solution. Any help would be greatly appreciated.

question from:https://stackoverflow.com/questions/65938158/jpa-mappedby-reference-an-unknown-target-entity

Answer 1

Try to correct this:

@Entity
public class Customer
{
    // ...

    @OneToMany(mappedBy = "orders", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private Set<Order> orders;
}

to this:

@Entity
public class Customer
{
    // ...

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

See additional explanation in the documentation.

And you should correct also your Product-Order @ManyToMany association. Only one side of this association should use @JoinTable other side should use mappedBy property of the @ManyToMany annotation. Something like this:

@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<>();
}

As it is stated in the documentation:

For @ManyToMany associations, the REMOVE entity state transition doesn’t make sense to be cascaded because it will propagate beyond the link table. Since the other side might be referenced by other entities on the parent-side, the automatic removal might end up in a ConstraintViolationException.

Also as this is explained in this section of the documentation:

If you forget to JOIN FETCH all EAGER associations, Hibernate is going to issue a secondary select for each and every one of those which, in turn, can lead to N+1 query issues.

For this reason, you should prefer LAZY associations.