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We had worked on a project where we hand-coded all of our DAOs. This produced four irksome difficulties: (1) Method names and implementations were not altogether consistent. (2) It was a pain to make additional columns sortable or filterable, and as a result, a lot of pages lacked good sorting and filtering. (3) Making additional DAOs was tedious and took a fair amount of time. (4) Writing tests for DAOs is tricky and tedious, so no one really did.

This framework aims to ease our troubles.

Why might you consider looking into this framework?

• Generic DAO: With the sweetness of Java generics, the concept of generic DAOs is not new, and it’s not difficult. However, we’ve put a lot of work into making these easy to use and robust. So if you like the way we’ve done it, then this framework provides ready-made code for you. On the other hand if you’d rather make your own, then simply feel free to look at our source code for ideas and help on a few potentially tricky issues.

• Search: Search is the most original and sophisticated part of this framework, and it can be used with or without the generic DAO portion of the framework. The search capability is designed around the use-case of a list page with sorting, filtering, column selection and paging. However, its use is certainly not limited to that. The value that the search adds is simpler, more robust querying with less coding and less testing. It is similar to Hibernate Criteria, but it is simpler to use and can easily move across layers of an application including view and even remote layers. Plus is works with both Hibernate and JPA^*.

• Remote DAO (for R.I.A.s?): If you you’re like us, you don’t want to write and configure an individual DAO style remote service for each entity in a R.I.A. or other client-heavy application. This framework may have the solution. We provide utilities and sample code to adapt our single general DAO to any remoting technology interface. Just configure this single remote access point and the client can do any basic CRUD or search operation on any entity. Again, if you don’t like our way of doing things, maybe you can at least get some ideas from our source code.

• Remote Search (for R.I.A.s?): As mentioned above, the framework can provide a single point for client-server CRUD and search operations. The framework’s search is meant to be able to cross the client-server boundary. So lists and searches in the client application can take advantage of the same easy-to-use features and consistency that the search functionality provides in the server tier or single tier application. This consistency allowed us to create a reusable collection type in Adobe Flex 3 that is associated with a single search object and automatically updates itself from the server according to the search parameters.^**

^*A fairly simple adapter is required for each JPA provider. Right now we only have an adapter for Hibernate Entity Manager. If anyone would like to contribute an adapter for any other JPA provider (OpenJPA, TopLink, etc.), that would be great.

^**If time permits, we would like to eventually post our corresponding Adobe Flex 3 framework and utilities.

More Information

Wiki Documentation: UserGuide

Javadoc: http://hibernate-generic-dao.googlecode.com/svn/trunk/docs/api/index.html

Blog: http://hibernategenericdao.wordpress.com/

Questions and Comments

Please post at http://groups.google.com/group/java-generic-dao.

Code Examples

Creating DAOs for individual model classes:

Simply extend the GenericDAO class with the specific type.

public interface ProjectDAO extends GenericDAO<Project, Long> { 



} 



public class ProjectDAOImpl extends GenericDAOImpl<Project, Long> implements ProjectDAO { 



}

The following methods (and several more) are now available on ProjectDAO

A GeneralDAO is also provided with DAO methods for any entity:

public interface GeneralDAO {
public <T> T find(Class<T> type, Serializable id);
public <T> T[] find(Class<T> type, Serializable ids);
public <T> T getReference(Class<T> type, Serializable id);
public <T> T[] getReferences(Class<T> type, Serializable ids);
public boolean save(Object entity); public boolean[] save(Object entities);
public boolean remove(Object entity); public void remove(Object entities);
public boolean removeById(Class<?> type, Serializable id);
public void removeByIds(Class<?> type, Serializable ids);
public <T> List<T> findAll(Class<T> type);
public List search(ISearch search); public Object searchUnique(ISearch search);
public int count(ISearch search); public SearchResult searchAndCount(ISearch search);
public boolean isAttached(Object entity);
public void refresh(Object entities); public void flush();
public Filter getFilterFromExample(Object example);
public Filter getFilterFromExample(Object example, ExampleOptions options); }

Search DTO usage examples

Search search = new Search(Project.class);

//filtering
search.addFilterEqual("name", "hibernate-generic-dao");

search.addFilterLessThan("completionDate", new Date());

search.addFilterOr(
Filter.equal("name", "Jack"),
Filter.and(
Filter.equal("name", "Jill"),
Filter.like("location", "%Chicago%"),
Filter.greaterThan("age", 5) )
);

search.addFilterIn("name", "Jack", "Jill", "Bob");

search.addFilterNot(Filter.in("name","Jack", "Jill", "Bob"));

//sorting
search.addSort("name");
search.addSort("age", true); //descending

//projection
search.addField("name");
search.addField("location");

//or with column operators
search.addField("rating", Field.OP_AVG);
search.addField("developerCount", Field.OP_MAX);

//paging
search.setMaxResults(15); //a.k.a. results per page
search.setPage(3);

//controlling eager fetching of relationships
serach.addFetch("owner");

Nested properties are also fully supported...

search.addFilterEqua("status.name", "active");
search.addFilterGreaterThan("workgroup.manager.salary", 75000.00);
search.addSort("status.name");

1. 指定users私有成员的类型为SET：set name="users"
2. 指定集合中的对象类型为User:<one-to-many class="paul.com.User"/>
3. 指定User对应的表：table="user"
4. 指定外键：<key column="room_id"/>
5. 指定如果同时新增、修改、删除关联的Room和User对象时，是否需要HIBERNATE执行两次操作：cascade="all"
6. 指定 lazy="extra"时，则集合中的元素不会被一起取出，而且要读SIZE时，只会发送一条COUNT的SQL语句至后台
7. 指定 inverse="true"时，当保存一的对象时，对应的多的对象不会同时被保存。

1. 指定名称为room成员的类型：many-to-one name="room"
2. 指定room对应的类名：class="paul.com.Room"
3. 指定外键：column="room_id"
4. 指定如果同时新增、修改、删除关联的Room和User对象时，是否需要HIBERNATE执行两次操作：cascade="all"
5. 指定关联两个表时的查询是否使用left-outer关键字：outer-join="true"

1. 指定名称为servers的私有成员的类型为SET：set name="servers"
   
2. 指定中间表为：table="user_server"
3. 指定User表与中间表关联的外键：key column="user_id"
4. 指定集合中的对象类型为：many-to-many class="paul.com.Server"
5. 指定中间表与Server关联的外键：column="server_id"
6. 指定如果同时新增、修改、删除关联的Room和User对象时，是否需要HIBERNATE执行两次操作：cascade="save-update"