It is a good idea to have those two layers when your business logic is more complex than your data logic. The service layer implements the business logic. In most cases, this layer has to perform more operations than just calling a method from a DAO object. And if you’re thinking of making your application … Read more
You can also try this code. It will preserve the items’ filetypes (.bas, .cls, .frm) Remember to refer to / Check the Microsoft Visual Basic For Applications Extensibility Library in VBE > Tools > References Public Sub ExportAllCode() Dim c As VBComponent Dim Sfx As String For Each c In Application.VBE.VBProjects(1).VBComponents Select Case c.Type Case … Read more
It’s definitely possible to extract it from Class#getGenericSuperclass() because it’s not defined during runtime, but during compiletime by FooDao extends BaseDao<Foo>. Here’s a kickoff example how you could extract the desired generic super type in the constructor of the abstract class, taking a hierarchy of subclasses into account (along with a real world use case … Read more
Ideally, Service layer (Manager) represents your business logic and hence it should be annotated with @Transactional. Service layer may call different DAOs to perform DB operations. Lets assume a situation where you have 3 DAO operations in a service method. If your 1st DAO operation failed, other two may be still passed and you will … Read more
One option is an “upsert” or combined append/update query. This old tip from Smart Access is one of my favourites: Update and Append Records with One Query By Alan Biggs Did you know that you can use an update query in Access to both update and add records at the same time? This is useful … Read more
Use merge(). The exception means that the current session is already aware of the entity you are passing. If not, check how you have overridden hashCode() and equals() – it should return different values for different entities.
For simple applications, I don’t see any problem in using the EntityManager directly from EJBs and skipping the DAO pattern (I’m tired of writing too much code). And my feeling is indeed that this is what JPA and the Java EE API encourage. But it may still be justified for more complex applications (for data … Read more
I found that using DAO in a specific manner is roughly 30 times faster than using ADO.NET. I am sharing the code and results in this answer. As background, in the below, the test is to write out 100 000 records of a table with 20 columns. A summary of the technique and times – … Read more
The Data Access Object is basically an object or an interface that provides access to an underlying database or any other persistence storage. That definition from: http://en.wikipedia.org/wiki/Data_access_object Check also the sequence diagram here: http://www.oracle.com/technetwork/java/dataaccessobject-138824.html Maybe a simple example can help you understand the concept: Let’s say we have an entity to represent an employee: public … Read more
I think transactions belong on the service layer. It’s the one that knows about units of work and use cases. It’s the right answer if you have several DAOs injected into a service that need to work together in a single transaction.