为什么 JPA 重复持久方法不抛出异常？

Question

Product product = new Product();
product.setName( "foo" );
product.setPrice(BigDecimal.valueOf( 4.5 ) );
pm.create( product ); // pm delegates calls to an entity manager object using persist method and tx is immediately commited after the call

List<Product> products = pm.findAllProducts();
products.stream().forEach( System.out::println ); // New product is listed too.

pm.create( product ); // Causes no exception! But, as per API, it should.

products = pm.findAllProducts(); // Fetch successful
products.stream().forEach( System.out::println ); // No difference from first print.

根据persistence API，如果实体已经存在，则坚持（从pm.create 调用）抛出EntityExistsException，但它不会按照代码发生。

1. 持久性提供程序 (PP) - EclipseLink。
2. 为什么 PP 忽略重复仍然存在？
3. PP 在什么情况下选择抛出异常？

编辑：

Product.java

注意：

1. 为简洁起见，排除了 getter 和 setter（适用于所有字段）和 toString()。
2. 我已尽力按照指南格式化代码，但它没有发生，请多多包涵。

@Entity @Table(name = "PRODUCTS") @XmlRootElement @NamedQueries({ @NamedQuery(name = "Product.findAll", query = "SELECT p FROM Product p") , @NamedQuery(name = "Product.findById", query = "SELECT p FROM Product p WHERE p.id = :id") , @NamedQuery(name = "Product.findByName", query = "SELECT p FROM Product p WHERE p.name like :name") , @NamedQuery(name = "Product.findByPrice", query = "SELECT p FROM Product p WHERE p.price = :price") , @NamedQuery(name = "Product.findByBestBefore", query = "SELECT p FROM Product p WHERE p.bestBefore = :bestBefore") , @NamedQuery(name = "Product.findByVersion", query = "SELECT p FROM Product p WHERE p.version = :version") , @NamedQuery(name = "Product.findTotal", query = "SELECT count(p.id), sum(p.price) FROM Product p WHERE p.id in :ids" })

公共类产品实现可序列化{

private static final long serialVersionUID = 1L;
@Id
@Basic(optional = false)
@NotNull
@SequenceGenerator( name="pidGen", sequenceName="PID_SEQ", allocationSize=1 )
@GeneratedValue( strategy=SEQUENCE, generator="pidGen" )
private Integer id;
@Basic(optional = false)
@NotNull
@Size(min = 3, max = 40, message="{prod.name}")
private String name;
// @Max(value=?)  @Min(value=?)//if you know range of your decimal fields consider using these annotations to enforce field validation
@Basic(optional = false)
@NotNull
@Max( value=1000, message="{prod.price.max}")
@Min( value=1, message="{prod.price.min}")
private BigDecimal price;
@Column(name = "BEST_BEFORE")
@Temporal(TemporalType.DATE)
//private Date bestBefore;
private LocalDate bestBefore;
@Version
private Integer version;

public Product() {
}

public Product(Integer id) {
    this.id = id;
}

public Product(Integer id, String name, BigDecimal price) {
    this.id = id;
    this.name = name;
    this.price = price;
}



@Override
public int hashCode() {
    int hash = 0;
    hash += (id != null ? id.hashCode() : 0);
    return hash;
}

@Override
public boolean equals(Object object) {
    // TODO: Warning - this method won't work in the case the id fields are not set
    if (!(object instanceof Product)) {
        return false;
    }
    Product other = (Product) object;
    if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
        return false;
    }
    return true;
}


 }

Answer 1

根据JPA Spec：

1. 如果 X 是一个新实体，它将成为托管实体。实体 X 将在或 在事务提交之前或作为刷新操作的结果。

2. 如果 X 是预先存在的托管实体，则持久操作将忽略它 (...)

3. 如果 X 是一个分离的对象，在持久化时可能会抛出 EntityExistsException 操作被调用，或者可能在刷新或提交时抛出 EntityExistsException 或另一个 PersistenceException

当您调用 EntityManager.persist(product) 时，product 成为托管实体 (#1)。任何后续对EntityManager.persist(product) 的调用都将被忽略，如#2 中所述。最后一点仅在您尝试在 分离的 实体上调用 persist() 时适用。