Question

根据此示例https://github.com/datanucleus/samples-jdo/blob/master/many_to_many_attributed/src/main/java/org/datanucleus/samples/jdo/many_many_attributed2/Main.java，我使用以下代码创建了CompanyProduct关系。

Company.java

@PersistenceCapable(identityType = IdentityType.APPLICATION, cacheable = "false", detachable = "true")
public class Company implements Serializable {
...
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
long id;
@Persistent
private String name = null;
@Persistent(defaultFetchGroup = "true", mappedBy = "company")
private Set<CompanyProduct> companyProduct = new HashSet<>(); 
...
}

Product.java

@PersistenceCapable(identityType = IdentityType.APPLICATION, cacheable = "false", detachable = "true")
public class Product implements Serializable {
...
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
long id;
@Persistent
private String name = null;
@Persistent(defaultFetchGroup = "true", mappedBy = "product")
private Set<CompanyProduct> companyProduct = new HashSet<>(); 
...
}

CompanyProduct.java

@PersistenceCapable(identityType = IdentityType.APPLICATION, cacheable = "false", detachable = "true")
public class CompanyProduct implements Serializable {
...
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
long id;
@Persistent
private String name = null;
@Persistent(defaultFetchGroup = "true")
private Company company;
@Persistent(defaultFetchGroup = "true")
private Product product; 
...
}

Main.java

...
tx.begin();
CompanyProduct companyProduct = new CompanyProduct();
Company company = pm.getObjectById(Company.class, companyId);
Product product= pm.getObjectById(Product.class, productId);

companyProduct.setCompany(company);
companyProduct.setProduct(product);

company.addCompanyProduct(companyProduct);
product.addCompanyProduct(companyProduct);

pm.makePersistent(companyProduct);
tx.commit();

...

删除关系

tx.begin();
CompanyProduct comProd= pm.getObjectById(CompanyProduct.class, companyProduct.getId());

comProd.removeCompanyProduct(comProd);
comProd.removeCompanyProduct(comProd);

pm.makePersistent(comProd);
tx.commit();

从关联对象中删除关系对象，会在提交后自动删除关系对象。如果我想将它重新添加到相关对象，我无法再次访问它。我在这里做错了什么？

Answer 1

我能够通过将依赖和依赖元素属性添加并设置为false来解决此自动删除问题。我按如下方式更新了我的代码;

Company.java

...
@Persistent(defaultFetchGroup = "true", mappedBy = "company", dependentElement = "false")
private Set<CompanyProduct> companyProduct = new HashSet<>(); 
...

Product.java

@Persistent(defaultFetchGroup = "true", mappedBy = "product", dependentElement = "false")
private Set<CompanyProduct> companyProduct = new HashSet<>();

CompanyProduct.java

...
@Persistent(defaultFetchGroup = "true", dependent = "false")
private Company company;
@Persistent(defaultFetchGroup = "true", dependent = "false")
private Product product; 
...

DataNucleus有很多归因关系。从相关对象中删除后删除Relation对象

1 个答案: