Creating a new ObjectContext each time does involve ‘some’ overhead. Essentially the overhead involved is copying metadata from a global cache into metadata associated with the specific ObjectContext. This overhead is relatively minor, so often it is not worth worrying about, especially when you consider the extra safety inherent in the using pattern. For me … Read more
The Hibernate configuration file must define the entity classes: <mapping class=”annotations.Users”/> Or you must explicitly add the class to the configuration using configuration.addClass(annotations.Users.class) // Read mappings as a application resourceName // addResource is for add hbml.xml files in case of declarative approach configuration.addResource(“myFile.hbm.xml”); // not hibernateAnnotations.cfg.xml
There are several way to solve it: As described in Do I need <class> elements in persistence.xml?, you can set hibernate.archive.autodetection property and Hibernate should be able to look up all annotated classes from classpath. However, that’s not JPA spec compliant. If you are using Spring, from Spring 3.1.2 (or probably even a bit earlier), … Read more
Not necessarily. There are three options: don’t override – thus you will be working with instances. This is fine in cases when you are working with the collections with only entities that are attached to the session (and hence guaranteed to be the same instance). This is (for me) the preferred way in many cases, … Read more
The error is fairly clear – you can’t bind directly to the query results, but need to populate some local collection instead. The simplest way to do this is to convert it to a List<T>, via ToList(): ddlCon.DataSource = (from em in dw.Employees select new { em.Title, em.EmployeeID }).ToList();
If you want a real database default value, use columnDefinition: @Column(name = “myColumn”, nullable = false, columnDefinition = “int default 100”) Notice that the string in columnDefinition is database dependent. Also if you choose this option, you have to use dynamic-insert, so Hibernate doesn’t include columns with null values on insert. Otherwise talking about default … Read more
Use EntityManager.detach. It makes the bean no longer linked to the EntityManager. Then set the Id to the new Id (or null if automatic), change the fields that you need and persist.
Structural annotation – nice. It is the first time I heard about this feature but it works. I just tried it. I will try to explain it little bit. Structural annotations are just random xml added to EDMX file. EDMX file is in fact just XML wich has 4 parts – CSDL, MSL, SSDL and … Read more
AsEnumerable() is effectively a cast to IEnumerable<T>, which makes member resolution find members of Enumerable instead of Queryable. It’s usually used when you want to force part of a query to run as SQL (or similar), and the remainder to run using LINQ to Objects. See my Edulinq blog post on it for more information. … Read more
You could do so. It’s technically possible. But it does (design)functionally not make any sense. You’re basically tight-coupling the model with the controller. Usually the JPA entity (model) is a property of a JSF managed bean (controller). This keeps the code DRY. You don’t want to duplicate the same properties over all place, let alone … Read more