java - 覆盖在父类中为 EntityManager 声明的持久化上下文 unitName。

Question

我有一个看起来像这样的通用 DAO 类:

public class GenericDaoJpa <T extends DomainObject> implements GenericDao<T> {

    private final Class<T> type;

    @PersistenceContext(type=PersistenceContextType.TRANSACTION, unitName="myPersistenceUnit")
    protected EntityManager entityManager;

    public GenericDaoJpa(Class<T> type) {
        super();
        this.type = type;
    }

    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }

    public T get(Object id) {
        return (T) entityManager.find(type, id);
    }
}

实现 DAO 类如下所示:

    @Repository("appDao")
    public class ProductDaoJpa extends GenericDaoJpa<Product> implements ProductDao{

    public ProductDaoJpa() {
        super(Product.class);
    }

    public List<Product> getAllProducts() {
        return getAll();
    }   
}

我为不同的数据库配置了另一个名为 mySecondPersistenceUnit 的持久单元。我想创建一个新的 DAO 类，它也将扩展 GenericDaoJpa 类，但使用不同的持久单元。如何扩展 GenericDaoJpa 类，但为每个 DAO 使用不同的持久单元？

我尝试将此声明移动到每个 DAO 类，但这会导致父类无法编译，因为它没有对 entityManager 的引用。

@PersistenceContext(type=PersistenceContextType.TRANSACTION, unitName="myPersistenceUnit")
protected EntityManager entityManager;

Answer 1

尝试改用方法注入(inject):

public class GenericDaoJpa <T extends DomainObject> implements GenericDao<T> {

    @PersistenceContext(type=PersistenceContextType.TRANSACTION, unitName="myPersistenceUnit")
    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }
}

而需要使用不同PU的子类:

@Repository("appDao")
public class ProductDaoJpa extends GenericDaoJpa<Product> implements ProductDao{

    @Override
    @PersistenceContext(type=PersistenceContextType.TRANSACTION, unitName="mySecondPersistenceUnit")
    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }
}