Question

我正在开发一个基本的Spring Boot零售商应用程序，该应用程序可跟踪产品，其制造商以及这些产品所属的类别。类别和产品之间存在多对多关系。当尝试保存添加了新产品的类别时，即使（category_id，product_id）的组合是唯一的，也会出现错误，表明我违反了唯一的主键约束。关于这是为什么以及如何解决的任何想法？

类别

@Entity
public class Category {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String name;

    @ManyToMany
    @JoinTable(name="product_categories", 
    joinColumns = @JoinColumn(name="category_id"), 
    inverseJoinColumns = @JoinColumn(name="product_id"))
    private Set<Product> products;

    `<rest of class omitted>`

产品

@Entity
public class Product {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String name;
    private double price;

    @ManyToOne
    private Manufacturer manufacturer;

    @ManyToMany(mappedBy = "products")
    private Set<Category> categories;

    '<rest of class omitted>'

DevBootstrap

    Manufacturer sony = new Manufacturer("Sony");
    manufacturerRepository.save(sony);

    Category console = new Category("Game Console");
    categoryRepository.save(console);

    Category robot = new Category("Robot");
    categoryRepository.save(robot);

    Category electronics = new Category("Electronic Device");
    categoryRepository.save(electronics);

    Product ps4 = new Product("Playstation 4", 300, sony);
    ps4.getCategories().add(electronics);
    ps4.getCategories().add(console);
    productRepository.save(ps4);
    electronics.getProducts().add(ps4);
    console.getProducts().add(ps4);
    categoryRepository.save(electronics);
    categoryRepository.save(console);
    sony.getProducts().add(ps4);
    manufacturerRepository.save(sony);

    Product aibo = new Product("AIBO Robotic Dog", 150, sony);
    aibo.getCategories().add(electronics);
    aibo.getCategories().add(robot);
    productRepository.save(aibo);
    electronics.getProducts().add(aibo);
    robot.getProducts().add(aibo);
    System.out.println("Ids: " + electronics.getId() + ", " + aibo.getId());
    categoryRepository.save(electronics); // <- Error occurs here
    categoryRepository.save(robot);
    sony.getProducts().add(aibo);
    manufacturerRepository.save(sony);

错误

org.h2.jdbc.JdbcSQLIntegrityConstraintViolationException: Unique index or primary key violation: "PUBLIC.PRIMARY_KEY_5 ON PUBLIC.PRODUCT_CATEGORIES(CATEGORY_ID, PRODUCT_ID) VALUES 1"; SQL statement:
insert into product_categories (category_id, product_id) values (?, ?) [23505-199]
    at org.h2.message.DbException.getJdbcSQLException(DbException.java:457) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.message.DbException.getJdbcSQLException(DbException.java:427) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.message.DbException.get(DbException.java:205) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.message.DbException.get(DbException.java:181) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.index.BaseIndex.getDuplicateKeyException(BaseIndex.java:103) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.mvstore.db.MVSecondaryIndex.checkUnique(MVSecondaryIndex.java:220) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.mvstore.db.MVSecondaryIndex.add(MVSecondaryIndex.java:196) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.mvstore.db.MVTable.addRow(MVTable.java:546) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.command.dml.Insert.insertRows(Insert.java:180) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.command.dml.Insert.update(Insert.java:132) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.command.CommandContainer.update(CommandContainer.java:133) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.command.Command.executeUpdate(Command.java:267) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.jdbc.JdbcPreparedStatement.executeUpdateInternal(JdbcPreparedStatement.java:200) ~[h2-1.4.199.jar:1.4.199]
    at org.h2.jdbc.JdbcPreparedStatement.executeUpdate(JdbcPreparedStatement.java:154) ~[h2-1.4.199.jar:1.4.199]
    at com.zaxxer.hikari.pool.ProxyPreparedStatement.executeUpdate(ProxyPreparedStatement.java:61) ~[HikariCP-3.2.0.jar:na]
    at com.zaxxer.hikari.pool.HikariProxyPreparedStatement.executeUpdate(HikariProxyPreparedStatement.java) ~[HikariCP-3.2.0.jar:na]
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:175) ~[hibernate-core-5.3.10.Final.jar:5.3.10.Final]
    ... 58 common frames omitted

Answer 1

您的代码中存在多个问题。

您错误地使用了save。请注意，CrudRepository.save method有一个返回值，文档说：

将返回的实例用于进一步的操作，因为保存操作可能已完全更改了实体实例。

您无需在ManyToMany的两侧都调用save来保持关系。一侧就足够了。
您的关系管理绝非习惯。我强烈建议您向产品添加addCategory方法，这将在Product.categories和Category.products中添加条目
最好还是重新考虑一下您的映射。对于玩具应用程序来说已经足够好了，但是您真的要拥有Category.products产品集吗？当您的数据库增大时，获取它会破坏性能。

为什么将此复合主键视为唯一键，我该如何解决？

1 个答案: