StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
primarykey
Id
9955424
data
AcceptedAnswerId
0
AnswerCount
0
ClosedDate
CommentCount
3
CommunityOwnedDate
CreationDate
2012-03-31T11:20:42.393
FavoriteCount
0
LastActivityDate
2012-03-31T11:20:42.393
LastEditDate
LastEditorUserId
0
OwnerUserId
472792
ParentId
9954761
PostTypeId
2
Score
20
ViewCount
0
LastEditorDisplayName
text
Body
Having a single class implement every DAO interface in your entire application would be a rather bad design. A more typical pattern is to have a <code>BaseDAO</code> interface (also often called <code>GenericDAO</code>) and have a <code>JPABaseDAO</code>, <code>JDBCBaseDAO</code> etc. These base classes will contain methods like find/get/read, save/store/persist, update/modify and delete/remove/purge. Specific DAO interfaces like <code>UserDAO</code> then inherit from <code>BaseDAO</code> and concrete implementations like <code>JPAUserDAO</code> extends from <code>JPABaseDAO</code>. A <code>BaseDAO</code> interface could look like this: <pre><code>public interface BaseDAO <T> { T getByID(Long ID); T save(T type); T update(T type); void delete(T type); } </code></pre> And a <code>UserDAO</code> interface: <pre><code>public interface UserDAO extends BaseDAO<User> { List<User> getAllAuthorized(); } </code></pre> Bare bones example of a <code>JPABaseDAO</code> implementing this interface: <pre><code>@Stateless public class JPABaseDAO<T> implements BaseDAO<T> { @PersistenceContext private EntityManager entityManager; private final Class<T> entityType; @SuppressWarnings("unchecked") public JPABaseDAO() { this.entityType = ((Class<T>) ((ParameterizedType) getClass().getGenericSuperclass()).getActualTypeArguments()[0]); } @Override public T getByID(Long ID) { return entityManager.find(entityType, ID); } @Override public T save(T type) { return entityManager.persist(type); } @Override public T update(T type) { return entityManager.merge(type); } @Override public void delete(T type) { entityManager.remove(entityManager.contains(type) ? type : entityManager.merge(type)); } } </code></pre> And some sample <code>UserDAO</code> implementation that would inherit from it: <pre><code>@Stateless public class JPAUserDAO extends JPABaseDAO<User> implements UserDAO { @PersistenceContext private EntityManager entityManager; @Override public List<User> getAllAuthorized() { return entityManager.createNamedQuery("User.getAllAuthorized", User.class) .getResultList(); } } </code></pre> In practice the base class can often do some other things transparently, for instance checking if an entity implements some kind of <code>Auditable</code> interface, and automatically setting the date and user that modified it, etc. When using EJB to implement your DAOs, one strategy to change implementations would be to put all JDBC implementations in one package and all JPA implementations in the other. Then just include only one implementation package in your build.
Tags
Title
singulars
PostAcceptedAnswerId
1. This table or related slice is empty.
PostParentId
1. PODAO design pattern
 singulars
 PostTypePostTypeId
 PTQuestion
PostTypePostTypeId
1. PTAnswer
UserLastEditorUserId
1. This table or related slice is empty.
UserOwnerUserId
1. USArjan Tijms
plurals
PostLinksPostIdRelatedPostId
1. This table or related slice is empty.
PostLinksRelatedPostIdPostId
1. This table or related slice is empty.
PostsAcceptedAnswerId
1. PODAO design pattern
 singulars
 PostTypePostTypeId
 PTQuestion
PostsParentIdCreationDate
1. This table or related slice is empty.
VotesPostIdCreationDate
1. VO
 singulars
 PostPostId
 PO
 UserUserId
 This table or related slice is empty.
 VoteTypeVoteTypeId
 VTUpMod
2. VO
 singulars
 PostPostId
 PO
 UserUserId
 This table or related slice is empty.
 VoteTypeVoteTypeId
 VTUpMod
3. VO
 singulars
 PostPostId
 PO
 UserUserId
 This table or related slice is empty.
 VoteTypeVoteTypeId
 VTUpMod
CommentsPostId
1. COExcellent, thank you very much. What about CRUD operations involving multiple tables? Would I, for example, execute a select statement to get an object and use it to call the CRUD of another DAO impl, or maybe create some kind of alien hybrid DAO ? Btw. you've been of great help to me, much appreciated.
 singulars
 PostPostId
 PO
 UserUserId
 USMercurial
2. COCRUD or whatever operations involving multiple entities/tables are often handled by Services that aggregate multiple DAOs. In EJB you'll be automatically within the same persistence context even if you call multiple DAOs (it propagates). Another possibility is that if entities are associated (User has-a House), you only need a DAO for a User and JPA will fetch/save/update houses automatically from your User objects.
 singulars
 PostPostId
 PO
 UserUserId
 USArjan Tijms

Querying!

Guidance

A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.