我正在从教程中学习 hibernate 中的多对多关系。我的示例项目有两个表，分别称为product_table 和order_table。我在这两个表之间使用了多对多关系。

在执行代码时，我在控制台中发现以下错误:

Exception in thread "main" org.hibernate.MappingException: Could not determine type for: java.util.Collection, at table: product_details, for columns: [org.hibernate.mapping.Column(orders)]
    at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:456)
    at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:423)
    at org.hibernate.mapping.Property.isValid(Property.java:226)
    at org.hibernate.mapping.PersistentClass.validate(PersistentClass.java:597)
    at org.hibernate.mapping.RootClass.validate(RootClass.java:265)
    at org.hibernate.boot.internal.MetadataImpl.validate(MetadataImpl.java:329)
    at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:459)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:710)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:726)
    at com.hibernatetest.main.MainApp.hibernateSession(MainApp.java:98)
    at com.hibernatetest.main.MainApp.main(MainApp.java:93)

这是我的 Hibernate 配置文件:

<!-- ~ Hibernate, Relational Persistence for Idiomatic Java ~ ~ License: 
    GNU Lesser General Public License (LGPL), version 2.1 or later. ~ See the 
    lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>. -->
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <session-factory>
    <!-- In case of using MySQL greater than 5 use MYSQL5 Dialect in stead of mysqldialect -->
        <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

        <!-- Assume test is the database name -->
        <property name="hibernate.connection.url">jdbc:mysql://localhost/hibernate_test?createDatabaseIfNotExist=true</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password"></property>


        <property name="show_sql">true</property>
        <property name="hbm2ddl.auto">create</property>

        <mapping class="com.hibernatetest.dto.ProductDetails" />
        <mapping class="com.hibernatetest.dto.OrderDetails" />


    </session-factory>
</hibernate-configuration>

这是我的 OrderDetails 类:

package com.hibernatetest.dto;

import java.util.ArrayList;
import java.util.Collection;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Entity
@Table(name = "product_details")
public class ProductDetails {

    private int productId;
    private String productName;
    @ManyToMany(mappedBy="product_details")
    private Collection<OrderDetails> orders=new ArrayList();

    public ProductDetails() {
    }

    public ProductDetails(String productName) {
        this.productName = productName;
    }

    @Id
    @Column(name = "product_id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    public int getProductId() {
        return productId;
    }

    public void setProductId(int productId) {
        this.productId = productId;
    }

    @Column(name = "product_name")
    public String getProductName() {
        return productName;
    }

    public void setProductName(String productName) {
        this.productName = productName;
    }


    public Collection<OrderDetails> getOrders() {
        return orders;
    }

    public void setOrders(Collection<OrderDetails> orders) {
        this.orders = orders;
    }



}

这是我的 OrderDetails 类:

package com.hibernatetest.dto;

import java.util.ArrayList;
import java.util.Collection;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.OneToMany;
import javax.persistence.OneToOne;
import javax.persistence.Table;

@Entity
@Table(name = "order_details")
public class OrderDetails {

    private int orderId;
    private String orderName;
    @ManyToMany
    private Collection<ProductDetails> products = new ArrayList();

    public OrderDetails() {
        super();
    }

    public OrderDetails(String orderName) {
        super();
        this.orderName = orderName;
    }

    @Id
    @Column(name = "order_id")
    @GeneratedValue(strategy = GenerationType.AUTO)
    public int getOrderId() {
        return orderId;
    }

    public void setOrderId(int orderId) {
        this.orderId = orderId;
    }

    @Column(name = "order_name")
    public String getOrderName() {
        return orderName;
    }

    public void setOrderName(String orderName) {
        this.orderName = orderName;
    }

    public Collection<ProductDetails> getProduct() {
        return products;
    }

    public void setProduct(Collection<ProductDetails> products) {
        this.products = products;
    }

}

这是 MainApp 类:

package com.hibernatetest.main;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

import com.hibernatetest.dto.Address;
import com.hibernatetest.dto.Office;
import com.hibernatetest.dto.OrderDetails;
import com.hibernatetest.dto.ProductDetails;
import com.hibernatetest.dto.UserDetails;

public class MainApp {

    public static void main(String[] args) {
        /*
         * UserDetails user = new UserDetails(); UserDetails user2=new UserDetails();
         * Address address1=new Address("test street1", "test city1", "test state",
         * "0000"); Address address2=new Address("test street2", "test city2",
         * "test state", "0001"); //user.setUserId(2); user.setUsername("Test User 1");
         * user2.setUsername("Test User 2"); user.setJoinedDate(new Date());
         * user2.setJoinedDate(new Date()); user.setHomeAddress(address1);
         * user.setOfficeAddress(address2); user2.setHomeAddress(address2);
         * user2.setOfficeAddress(address1); user.setDescription("test data 1");
         * user2.setDescription("test data 2"); user.setJoinedTime(new Date());
         * user2.setJoinedTime(new Date());
         * 
         * String officePhone1="00000000"; String officePhone2="00000001"; String
         * officePhone3="00000002"; Collection<String> phoneNumbers=new
         * ArrayList<String>(); phoneNumbers.add(officePhone1);
         * phoneNumbers.add(officePhone2); phoneNumbers.add(officePhone3); Office
         * office=new Office(1,"Test Office 1", address1,phoneNumbers);
         * 
         * SessionFactory sessionFactory = new
         * Configuration().configure().buildSessionFactory();
         * 
         * Session session = sessionFactory.openSession();
         * 
         * session.beginTransaction();
         * 
         * session.save(user); session.save(user2); session.save(office);
         * 
         * session.getTransaction().commit();
         * 
         * session.close();
         * 
         * user=null;
         * 
         * session= sessionFactory.openSession(); session.beginTransaction();
         * user=session.get(UserDetails.class,2);
         * 
         * System.out.println(user.getUserId()+" "+user.getDescription());
         * 
         * session.close(); office=null; session=sessionFactory.openSession();
         * session.beginTransaction(); office=session.get(Office.class, 1);
         * System.out.println(office.getOfficeName()); session.close();
         * System.out.println(office.getPhoneList().size());
         */

        ProductDetails product1 = new ProductDetails("Sample product 1");
        ProductDetails product2 = new ProductDetails("Sample product 2");
        ProductDetails product3 = new ProductDetails("Sample product 3");
        ProductDetails product4 = new ProductDetails("Sample product 4");
        OrderDetails order1 = new OrderDetails("Order No 1");
        OrderDetails order2 = new OrderDetails("Order No 2");

        product1.getOrders().add(order1);
        product1.getOrders().add(order2);
        product2.getOrders().add(order2);


        order1.getProduct().add(product1);
        order1.getProduct().add(product2);
        order1.getProduct().add(product3);
        order2.getProduct().add(product1);
        order2.getProduct().add(product3);
        order2.getProduct().add(product4);

        List<Object> insetableObjects = new ArrayList<Object>();
        insetableObjects.add(product1);
        insetableObjects.add(product2);
        insetableObjects.add(product3);
        insetableObjects.add(product4);
        insetableObjects.add(order1);
        insetableObjects.add(order2);
        hibernateSession(insetableObjects);

    }

    public static void hibernateSession(List<Object> collection) {
        SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();

        Session session = sessionFactory.openSession();

        session.beginTransaction();

        for (Object obj : collection) {
            session.save(obj);
            System.out.println("Object Added");
        }

        session.getTransaction().commit();
        session.close();
    }
}

请指导我执行后续步骤，并提前致谢。

最佳答案

参见this tutorial和 Jack Flamp的评论。为了建立 ManyToMany 关系，您需要一个 @JoinTable 引用您要在其特定类中使用的表，并在另一个类中引用。例如，在您的情况下，它会是这样的:

产品详细信息:

@Entity
@Table(name = "product_details")
public class ProductDetails {

    private int productId;
    private String productName;

    @ManyToMany(cascade = { CascadeType.ALL })
    @JoinTable(
        name = "order_product", 
        joinColumns = { @JoinColumn(name = "productId") }, 
        inverseJoinColumns = { @JoinColumn(name = "orderId") }
    )
    private Collection<OrderDetails> orders = new ArrayList();

    [...]

订单详情:

@Entity
@Table(name = "order_details")
public class OrderDetails {

    private int orderId;
    private String orderName;
    @ManyToMany(mappedBy = "orders")
    private Collection<ProductDetails> products = new ArrayList();

在这里，您的“拥有方”(=持有信息的一方)是产品。您的产品可以有多个订单，一个订单属于多个产品。当然，如果不符合您的需求，请随意恢复它们。我给您的链接很好地解释了每个注释的作用。

编辑:确保(在示例中)order_product 表确实存在。否则，它将无法工作。

关于java - Hibernate 无法确定多对多关系中 : java. util.Collection 的类型，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/49768271/