Hibernate 中的通用 DAO 模式

Question

在处理 Hibernate 时，我们遵循 Hibernate Doc 中提到的通用 Hibernate DAO 模式。

因此，据此，我们目前维持两个平行的等级制度 1) 对于接口 2）对于实现，

因此如果我们以这种方式工作，即使除了标准持久性方法之外没有提出新方法，我们也需要为该条目及其实现创建一个标记接口。

尽管这种方法及其明确的分离似乎没有问题。

我的问题是是否有更好的方法/替代方法来实现此目的

提前致谢

Answer 1

Umesh 我将向您展示如何实现此功能

接口

public interface Repository<INSTANCE_CLASS, PRIMARY_KEY_CLASS> {

    void add(INSTANCE_CLASS instance);
    void merge(INSTANCE_CLASS instance);
    void remove(PRIMARY_KEY_CLASS id);
    INSTANCE_CLASS findById(PRIMARY_KEY_CLASS id);
    INSTANCE_CLASS findById(PRIMARY_KEY_CLASS id, Class fetchingStrategy, Object... args);
    List<INSTANCE_CLASS> findAll();
    List<INSTANCE_CLASS> findAll(Class fetchingStrategy, Object... args);
    List<INSTANCE_CLASS> findAll(int pageNumber, int pageSize);
    List<INSTANCE_CLASS> findAll(int pageNumber, int pageSize, Class fetchingStrategy, Object... args);
    List<INSTANCE_CLASS> findAllByCriteria(Criteria criteria);
    List<INSTANCE_CLASS> findAllByCriteria(Criteria criteria, Class fetchingStrategy, Object... args);
    List<INSTANCE_CLASS> findAllByCriteria(int pageNumber, int pageSize, Criteria criteria);
    List<INSTANCE_CLASS> findAllByCriteria(int pageNumber, int pageSize, Criteria criteria, Class fetchingStrategy, Object... args);

}

因为您通常不需要上面显示的所有方法，所以我们创建一个抽象类其目的是作为虚拟实现 >

public abstract class AbstractRepository<INSTANCE_CLASS, PRIMARY_KEY_CLASS> implements Repository<INSTANCE_CLASS, PRIMARY_KEY_CLASS> {

    public void add(INSTANCE_CLASS instance) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public void merge(INSTANCE_CLASS instance) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public void remove(PRIMARY_KEY_CLASS id) {
        throw new UnsupportedOperationException("Not supported yet.");
    }


    public INSTANCE_CLASS findById(PRIMARY_KEY_CLASS id) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public INSTANCE_CLASS findById(PRIMARY_KEY_CLASS id, Class fetchingStrategy, Object... args) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List<INSTANCE_CLASS> findAll() {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List<INSTANCE_CLASS> findAll(Class fetchingStrategy, Object... args) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List<INSTANCE_CLASS> findAll(int pageNumber, int pageSize) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List<INSTANCE_CLASS> findAll(int pageNumber, int pageSize, Class fetchingStrategy, Object... args) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List<INSTANCE_CLASS> findAllByCriteria(Criteria criteria) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List<INSTANCE_CLASS> findAllByCriteria(Criteria criteria, Class fetchingStrategy, Object... args) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List<INSTANCE_CLASS> findAllByCriteria(int pageNumber, int pageSize, Criteria criteria) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List<INSTANCE_CLASS> findAllByCriteria(int pageNumber, int pageSize, Criteria criteria, Class fetchingStrategy, Object... args) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

}

现在，例如，如果您想要一个仅需要添加方法的存储库，您可以使用

public class PersonRepository extends AbstractRepository<Person, Integer> {

    public void add(Person instance) {
        /**
          * person implmentatiuon goes here
          */    
    }

}

如果其他开发人员尝试访问除添加方法之外的其他方法，他或她将得到UnsupportedOperationException

Criteria 只是标记界面。

public interface Criteria {}

某些方法定义参数类 fetchingStrategy 的目的是为了匹配外部化命名查询。这样，我就避免了容易出错的手工编码字符串。例如，JSR-303 bean 验证使用此方法来验证组属性。请参阅 这里

public class Person {
    public static interface PERSON_WITH_ADDRESS {}
}

外部化命名查询如下所示

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <query name="PERSON_WITH_ADDRESS">
        <![CDATA[
            from 
                Person p
            left join fetch 
                p.address
        ]]>
    </query>
</hibernate-mapping>

所以当我想检索所有具有地址的人时，我调用

PersonRepository<Person, Integer> respository ...

List<Person> personList = repository.findAll(PERSON_WITH_ADDRESS.class);

findAll 可以写为

public class PersonRepository extends AbstractRepository<Person, Integer> {

    List<Person> findAll(Class fetchingStrategy, Object... args) {
        if(fetchingStrategy.isAssignableFrom(PERSON_WITH_ADDRESS.class)) {
            sessionFactory.getCurrentSession()
                          .getNamedQuery(fetchingStrategy.getSimpleName())
                          .list();
        }

        throw new UnsupportedOperationException("Not supported yet.");
    }

}