Hibernate 中的通用 DAO 模式

Question

在开发 hibernate 时，我们也遵循 Hibernate Doc 中提到的通用 Hibernate DAO 模式。

因此，我们目前正在维护两个并行的层次结构 1) 用于接口 2）用于实现

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议的新方法，我们也需要为该条目及其实现创建一个标记接口。

虽然这种方法和明确的分离似乎没有问题。

我的问题是是否有更好的方法/替代方法来实现这一目标

提前致谢

Answer 1

Umesh 我将向您展示我们如何实现此功能

界面

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，所以我们创建了一个抽象类目的是作为一个虚拟实现

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，如果你想要一个只需要添加方法的存储库，你可以使用

public class PersonRepository extends AbstractRepository<Person, Integer> {

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

}

如果其他开发者尝试访问 add 方法以外的方法，他或她将得到 UnsupportedOperationException

条件只是一个标记界面。

public interface Criteria {}

一些方法定义参数Class fetchingStrategy的目的是为了匹配外部化的命名查询。这样，我避免了容易出错的手工编码字符串。例如，JSR-303 bean 验证使用这种方法来验证 groups 属性。见here

public class Person {
    public static interface PERSON_WITH_ADDRESS {}
}

externalize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有地址的人时，我打电话

PersonRepository<Person, Integer> respository ...

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

findAll 可以写成

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.");
    }

}